Dissertations / Theses: 'Quantra'

1

Ekpo, Ernest Usang. "Measurement of breast density with Digital Mammography and Tomosynthesis." Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/15539.

Full text

Abstract:

Aims: The potential applicability of breast density (BD) information in clinical decision-making is limited by variability in its assessment. This thesis explores novel tools for BD assessment and mammography display. Firstly, it examines the literature regarding BD, factors that impact upon BD, such as diet and physical activity, and tools for BD measurement. Secondly, it assesses inter-reader agreement in BD assessment using the 5th edition BI-RADS® rating scale. Thirdly, it examines the agreement in BD assessment between QuantraTM (Hologic, Bedford, MA) and BI-RADS® and the performance of QuantraTM in reproducing BI-RADS® assessment with digital mammography (DM). Fourthly, it explores BD of digital breast tomosynthesis (DBT) using QuantraTM and its agreement with BI-RADS® rating. Lastly, it evaluates the performance characteristics of EIZO RX850 and compares it to two currently used mammography display technologies (EIZO GS510 and Barco MDCG 5121). Methods: The study was performed in four phases. In phase 1, five radiologists performed BD assessment of 1000 digital mammogram using the 5th edition BI-RADS® scheme , with a repeat assessment of 100 mammograms. A weighted Kappa was used to calculate intra- and inter-reader agreement. In phase 2, QuantraTM (v.2.0) and BI-RADS® BD assessment was performed on 1314 mammogram during clinical mammography interpretation, with six radiologists involved across the BI-RADS® assessment. A repeat BI-RADS® assessment of 292 cases was performed by three radiologists. Both simple and weighted Kappa were used to calculate agreement between QuantraTM and BI-RADS®, and Receiver Operating Characteristic (ROC) analysis was used to assess the performance of QuantraTM in reproducing BI-RADS® assessment. In phase 3, BD of 234 women undergoing DBT examination was assessed using QuantraTM (v.2.1.1), with BI-RADS® assessment of these women performed using prior mammograms together with the 2D images synthesized from DBT. A weighted Kappa and ROC were used to compare the BD assessments of QuantraTM and BI-RADS®. In phase 4, the performance characteristics of EIZO RX850 was assessed and compared to that of EIZO GS510 and Barco MDCG 5121 according to the American Physicist in Medicine Task Group-18 criteria. Image J software package was used to assess and compare the conspicuity index of lesions on the three monitors. Results: In phase 1, overall BI-RADS® inter-reader agreement (Kw) was substantial 0.79 (95%CI: 0.78 – 0.83) on a four-grade scale and almost perfect on a two-grade scale 0.88 (95%CI: 0.87 – 0.89). In phase 2, agreement (Kw) between QuantraTM and BI-RADS® ranged from 0.73 (95%CI: 0.68 – 0.82) to 0.79 (95%CI: 0.76 – 0.87) on a four-grade scale and 0.84 (95%CI: 0.79 – 0.87) to 0.85 (95%CI: 0.80 – 0.90) on a two-grade scale. QuantraTM demonstrated limited performance in reproducing BI-RADS® assessment on a four-grade scale, however, highly reproduced BI-RADS® on a two-grade scale, with sensitivity ranging from 91.3% to 93.2% and specificity ranging from 83.6% to 86.1%. In phase 3, agreement between QuantraTM and BI-RADS® ranged from 0.77 (95%CI: 0.45 – 0.89) to 0.87 (95%CI: 0.82 – 0.90) on a four-category scale and 0.83 (95%CI: 0.76 – 0.87) to 0.87 (95%CI: 0.83 – 0.89) on a two-grade scale. QuantraTM distinguished BI-RADS® A–B from C–D with 97.1% sensitivity and 83.1% specificity. In phase 4, the performance characteristics of EIZO RX850, EIZO GS510, and Barco MDCG5121 respectively were: maximum luminance (490, 500.5, and 413 cd/m2), minimum luminance (0.724, 1.170, and 0.92 cd/m2), contrast ratio (675:1, 428:1, 449:1), just-noticeable difference (635, 622, 609), non-uniformity (20, 5.92, and 8.5%), veiling glare (GR=2465.6, 720.4, 1249.8), and color uniformity (Δu′v′=+0.003, +0.002, +0.002). There were no statistically significant differences in conspicuity of lesions on the three monitors evaluated (P< 0.05). Conclusion: Overall, BI-RADS® inter-reader agreement in BD assessment is better on a two-grade scale than on a four-grade scale. QuantraTM BD measures from DM reflects 4th edition BI-RADS® and measures from DBT reflects 5th edition BI-RADS® rating on a two-grade scale. EIZO RX850 has equal to or better performance characteristics than those of the Barco MDCG 5121 and EIZO GS510 displays. Data produced should be helpful for tailoring clinical decisions from BD to improve women’s health and to educate health-care managers about these novel tools and facilitate better decision-making regarding their clinical implementation.

APA, Harvard, Vancouver, ISO, and other styles

2

Fontoura, Carlos Eduardo S. [UNESP]. "Quebra da simetria de sabor na interação de mésons charmosos com o núcleon." Universidade Estadual Paulista (UNESP), 2011. http://hdl.handle.net/11449/102548.

Full text

Abstract:

Made available in DSpace on 2014-06-11T19:32:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-12-02Bitstream added on 2014-06-13T20:03:18Z : No. of bitstreams: 1 fontoura_ces_dr_ift.pdf: 1611387 bytes, checksum: 1d3655696458409c2d813244b522c22d (MD5)
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Nós empregamos modelos de quarks para investigar a quebra da simetria de sabor na interação de mésons e bárions charmosos com o núcleon. Nesses modelos a única fonte de quebra da simetria de sabor são as massas dos quarks u, d, s e c. Inicialmente, empregamos o modelo de decaimento forte 3P0 para calcular constantes de acoplamento hádron-hádron efetivas. Os elementos de matriz do operador de decaimento 3P0 foram calculados usando funções de onda hadrônicas determinadas através da diagonalização exata do Hamiltoniano microscópico de um modelo não-relativístico de quarks em uma base ﬁnita de funções de onda Gaussianas. Resultados numéricos foram obtidos para as amplitudes ππρ, KKρ, ¯D¯Dρ, NNπ, NΣsK, NΛc ¯D, NΣc ¯D, NΛsK e os efeitos da quebra de simetria foram avaliados para as correspondentes constantes de acoplamento. A seguir, investigamos o espalhamento a baixas energias dos mésons estranhos K e charmosos ¯D com o núcleon empregando um modelo microscópico de quarks inspirado na cromodinâmica quântica no calibre de Coulomb que conﬁna a carga de cor e realiza a quebra dinâmica da simetria quiral. O Hamiltoniano microscópico do modelo incorpora um potencial de conﬁnamento do tipo Coulomb e uma interação hiperﬁna de glúons transversos. Uma função de massa para os quarks constituintes ´e obtida pela solu¸c˜ao de uma equação de gap e funções de onda de estados ligados de mésons e bárions são obtidas no espaço de Fock usando um esquema de cálculo variacional. A seguir, tendo obtido as massas constituintes e as funções de ondas dos hádrons, uma interação efetiva méson-núcleon de alcance curto é derivada a partir do mecanismo de troca quark-glúon. Para descrever a física...
We employ quark models to investigate the breaking of ﬂavor symmetry in the interaction of charmed mesons and baryons with the nucleon. The only source of ﬂavor symmetry breaking are the masses of the quarksu,d,s, andc. Initially, we employ the 3 P0 strong decay model to obtain hadron-hadron eﬀective coupling constants. The matrix elements of the3P0 decay operator were evaluated employing hadron wave-functions calculated by exact diagonalization of the microscopic quark model Hamiltonian in a ﬁnite basis of Gaussian wave-functions. Numerical results were determined for theππρ,KKρ, ¯ D¯Dρ,NNπ,NΣsK,NΛc ¯D,NΣc ¯D,NΛsK amplitudes and the symmetry breaking effects were evaluated for the corresponding coupling constants. Next, we investigate the strong interaction of strangeK and charmed ¯D mesons by nucleons at low energies using a microscopic quark model inspired in quantum chromodynamics in Coulomb gauge that conﬁnes color and realizes dynamical chiral symmetry breaking. The microscopic model Hamiltonian incorporates a conﬁning Coulomb potential and a transverse-gluon hyperﬁne interaction. A constituent-quark mass function is obtained by solving a gap equation and baryon and meson bound-states are obtained in Fock space using a variational calculation. Next, having obtained the constituent-quark masses and the hadron waves functions, an eﬀective short-range meson-nucleon interaction is derived from a quark-interchange mechanism. To describe long-distance physics vector- and scalar-meson exchanges obtained from eﬀective Lagrangians are incorporated. The derived eﬀective meson-baryonpotential is used in a Lippmann-Schwinger equation to obtain cross section and phase shifts. The obtained results are compared with recent similar calculations using the nonrelativistic... (Complete abstract click electronic access below)

APA, Harvard, Vancouver, ISO, and other styles

3

Capdevilla, Roldan Rodolfo Maia [UNESP]. "Dynamical chiral symmetry breaking: the fermionic gap equation with dynamical gluon mass and confinement." Universidade Estadual Paulista (UNESP), 2013. http://hdl.handle.net/11449/92026.

Full text

Abstract:

Made available in DSpace on 2014-06-11T19:25:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-02-28Bitstream added on 2014-06-13T20:53:39Z : No. of bitstreams: 1 capdevillaroldan_rm_me_ift.pdf: 1695600 bytes, checksum: 56f8cc2724bbe924e0b430ebe1a3b24e (MD5)
Alguns aspectos da quebra de simetria quiral para quarks na representação fundamental são discutidos no contexto das equações de Schwinger-Dyson. Estudamos a equação de gap fermionica incluindo o efeito de uma massa dinêmica para os gluons. Ao estudar esta equação de gap verificamos que a intenção não é forte o suficiente para gerar uma massa dinâmica dos quarks compatível com os dados experimentais. Também discutimos como a introdução de um propagador confinante pode mudar este cenário, exatamente como foi proposto por Cornwall [1] recentemente, desta forma estudamos uma equação de gap completa, composta pela troca de um gluon massivo e por um termo confinante; M('p POT 2') = 'M IND. c('p POT 2') + 'M IND. 1g'('p POT 2'). Encontramos soluções assintótica desta equação de gap nos casos de constante de acoplamento constante e corredora. Este último caso corresponde a um aprimoramento do cálculo com constante de acoplamento constante feito por Doff, Machado e Natale [2]
Some aspects of chiral symmetry breaking for quarks in the fundamental representation are discussed in the framework of the Schwinger-Dyson equations. We study the fermionic gap equation including effects of dynamical gluon mass. Studying the bifurcation equation of this gap equation we verify that the interaction is not strong enough to generate a satisfactory dynamical quark mass. We also discuss how the introduction of a confining propagator may change this scenario as recently pointed out by Cornwall [1], so we study a complete gap equation composed by the one-dressed-gluon exchange term and a confining term: M('p POT 2') = 'M IND. c('p POT 2') + 'M IND. 1g'('p POT 2'). We find asymptotic solutions for this gap equation in the cases of constant coupling and running coupling constant. This last case is an improvement of the constant coupling calculation of Doff, Machado and Natale [2]

APA, Harvard, Vancouver, ISO, and other styles

4

Ceballos, Russell R. "LINEARITY VERSUS COMPLETE POSITIVITY OF THE EVOLUTION OF OPEN QUANTUM SYSTEMS." OpenSIUC, 2014. https://opensiuc.lib.siu.edu/theses/1420.

Full text

Abstract:

The title may be a bit misleading. Perhaps, "On the Complete Positivity of Reduced Quantum Dynamics," would be a more fitting title. Determining whether or not completely positive (CP) maps are required to describe open system quantum dynamics is an extremely important issue concerning the fundamental mathematical foundations of QM, as well as many other areas of physics. it had been typically believed that only CP maps actually describe the dynamical evolution of open quantum systems, however there has been speculation as to whether this is a strict constraint on the mathematical and physical structure of stochastic quantum dynamical maps. The objective of this thesis is to demonstrate that given a particular unitary operator, an initial system state, a final system state, and the dimension of the environment state, there exists no CP map with a composite system-environment, product initial state that is compatible with the given constraints on the reduced quantum dynamics of the system under investigation.

APA, Harvard, Vancouver, ISO, and other styles

5

Fanchini, Felipe Fernandes. "Estudo da decoerência e da dissipação quântica durante a evolução temporal de dois qubits ditadas por operações unitárias controladas." Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-09042008-110046/.

Full text

Abstract:

Nessa dissertação, abordamos o problema de dois qubits interagindo com campos externos e entre si controladamente, de acordo com um Hamiltoniano considerado realista para implementação da porta lógica quântica XOR. Introduzimos acoplamentos entre as observáveis do sistema de dois qubits e um banho de osciladores harmônicos a fim de tratarmos o problema da dissipação e da decoerência. Primeiramente nós consideramos o limite no qual a decoerência é mais rápida que qualquer processo gerado pelo Hamiltoniano do sistema. Prosseguimos então, através do método numérico conhecido como Integrador Unitário, com o estudo da matriz densidade do sistema durante a operação da porta lógica quântica sem incluir, inicialmente, o acoplamento com o banho de osciladores harmônicos. Finalmente, implementamos o método numérico conhecido como Propagador quase adiabático para estudar a decoerência e a dissipação durante a operação da porta lógica quântica XOR, a fim de analisarmos os aspectos perturbativos do sistema quântico de dois qubits.
In this dissertation, we approach the problem of two qubits interading with themselves and with externa1 fields in a controlled way, according to a Hamiltonian considered realistic to implement the XOR quantum gate. We introduce couplings between the observables of the two-qubits system and of a bath of harmonic oscillators, to treat the problems of dissipation and decoherence. Preliminarly, we consider the limit in which decoherence is faster than any process dictated by the Hamiltonian evolution of the system. Then, through a unitary-integrator numerical method, we proceed with the study of the evolution of the density matrix of the system during the operation of the logical quantum gate, initially, without the coupling with the bath of harmonic oscillators. Finally, we use the quasiadiabatic path integral method to study the dissipation and decoherence during the logical operation, through the inclusion of the bath.

APA, Harvard, Vancouver, ISO, and other styles

6

Joshi, Darshan Gajanan. "Magnetic quantum phase transitions: 1/d expansion, bond-operator theory, and coupled-dimer magnets." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-198634.

Full text

Abstract:

In the study of strongly interacting condensed-matter systems controlled microscopic theories hold a key position. Spin-wave theory, large-N expansion, and $epsilon$-expansion are some of the few successful cornerstones. In this doctoral thesis work, we have developed a novel large-$d$ expansion method, $d$ being the spatial dimension, to study model Hamiltonians hosting a quantum phase transition between a paramagnet and a magnetically ordered phase. A highlight of this technique is that it can consistently describe the entire phase diagram of the above mentioned models, including the quantum critical point. Note that most analytical techniques either efficiently describe only one of the phases or suffer from divergences near the critical point. The idea of large-$d$ formalism is that in this limit, non-local fluctuations become unimportant and that a suitable product state delivers exact expectation values for local observables, with corrections being suppressed in powers of $1/d$. It turns out that, due to momentum summation properties of the interaction structure factor, all diagrams are suppressed in powers of $1/d$ leading to an analytic expansion. We have demonstrated this method in two important systems namely, the coupled-dimer magnets and the transverse-field Ising model. Coupled-dimer magnets are Heisenberg spin systems with two spins, coupled by intra-dimer antiferromagnetic interaction, per crystallographic unit cell (dimer). In turn, spins from neighboring dimers interact via some inter-dimer interaction. A quantum paramagnet is realized for a dominant intra-dimer interaction, while a magnetically ordered phase exists for a dominant (or of the same order as intra-dimer interaction) inter-dimer interaction. These two phases are connected by a quantum phase transition, which is in the Heisenberg O(3) universality class. Microscopic analytical theories to study such systems have been restricted to either only one of the phases or involve uncontrolled approximations. Using a non-linear bond-operator theory for spins with S=$1/2$, we have calculated the $1/d$ expansion of static and dynamic observables for coupled dimers on a hypercubic lattice at zero temperature. Analyticity of the $1/d$ expansion, even at the critical point, is ensured by correctly identifying suitable observables using the mean-field critical exponents. This method yields gapless excitation modes in the continuous symmetry broken phase, as required by Goldstone\'s theorem. In appropriate limits, our results match with perturbation expansion in small ratio of inter-dimer and intra-dimer coupling, performed using continuous unitary transformations, as well as the spin-wave theory for spin-$1/2$ in arbitrary dimensions. We also discuss the Brueckner approach, which relies on small quasiparticle density, and derive the same $1/d$ expansion for the dispersion relation in the disordered phase. Another success of our work is in describing the amplitude (Higgs) mode in coupled-dimer magnets. Our novel method establishes the popular bond-operator theory as a controlled approach. In $d=2$, the results from our calculations are in qualitative agreement with the quantum Monte Carlo study of the square-lattice bilayer Heisenberg AF spin-$1/2$ model. In particular, our results are useful to identify the amplitude (Higgs) mode in the QMC data. The ideas of large-$d$ are also successfully applied to the transverse-field Ising model on a hypercubic lattice. Similar to bond operators, we have introduced auxiliary Bosonsic operators to set up our method in this case. We have also discussed briefly the bilayer Kitaev model, constructed by antiferromagnetically coupling two layers of the Kitaev model on a honeycomb lattice. In this case, we investigate the dimer quantum paramagnetic phase, realized in the strong inter-layer coupling limit. Using bond-operator theory, we calculate the mode dispersion in this phase, within the harmonic approximation. We also conjecture a zero-temperature phase diagram for this model.

APA, Harvard, Vancouver, ISO, and other styles

7

Hessmo, Björn. "Quantum optics in constrained geometries." Doctoral thesis, Uppsala University, Department of Quantum Chemistry, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-1208.

Full text

Abstract:

When light exhibits particle properties, and when matter exhibits wave properties quantum mechanics is needed to describe physical phenomena.

A two-photon source produces nonmaximally entangled photon pairs when the source is small enough to diffract light. It is shown that diffraction degrades the entanglement. Quantum states produced in this way are used to probe the complementarity between path information and interference in Young's double slit experiment.

When two photons have a nonmaximally entangled polarization it is shown that the Pancharatnam phase is dependent on the entanglement in a nontrivial way. This could be used for implementing simple quantum logical circuits.

Magnetic traps are capable of holding cold neutral atoms. It is shown that magnetic traps and guides can be generated by thin wires etched on a surface using standard nanofabrication technology. These atom chips can hold and manipulate atoms located a few microns above the surface with very high accuracy. The potentials are very versatile and allows for highly complex designs, one such design implemented here is a beam splitter for neutral atoms. Interferometry with these confined de Broglie is also considered. These atom chips could be used for implementing quantum logical circuits.

APA, Harvard, Vancouver, ISO, and other styles

8

Canova, André Luiz Fassone [UNESP]. "Estudo químico quântico relativístico das propriedades eletrônicas e estruturais dos compostos Aun(n=1-5), AuOn-e AuSn - (n=1-2) e AuH." Universidade Estadual Paulista (UNESP), 2014. http://hdl.handle.net/11449/116003.

Full text

Abstract:

Made available in DSpace on 2015-03-03T11:52:52Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-07-21Bitstream added on 2015-03-03T12:06:57Z : No. of bitstreams: 1 000808608.pdf: 1523686 bytes, checksum: f545c7465c56b46cea6da94906c9f8a7 (MD5)
Os efeitos relativístico estão mais próximos de nós do que pensamos, com por exemplo: na cor do metal Ouro, no funcionamento da bateria Chumbo-ácido entre outros. Os efeitos relativísticos são mais intensos em átomos pesados, sobretudo no átomo de Ouro, desempenhando um papel essencial para a interpretação dos fenômenos de natureza quântica, visto que os seus efeitos tendem a alterar significativamente a energia e a geometria dos sistemas. Quando comparados aos resultados obtidos pela utilização de metodologias não relativísticas (HF) e quasi relativística (ZORA) podemos perceber claramente a influência das consequências da Teoria da Relatividade, como por exemplo: o acoplamento spin-órbita e a quebra da degenerescência na enrgia dos orbitais. Nesse trabalho, iremos utilizar as metodologias relativísticas de Dirac-Hartree-Fock (DHF) e Teoria do Funcional de Densidade (DFT) para o estudo de sistemas compostos por átomos de Ouro e demonstraremos que, apesar do elevado custo computacional envolvido, as metodologias relativísticas devem ser a primeira opção de escolha dada a excelente qualidade dos resultados obtidos, em propriedades geométricas eletrônicas, tais como: a distância de ligação e Afinidade Eletrônica. Particularmente no estudo da molécula de Au2 obtivemos excelente resultado para a distância de ligação, pois a divergência entre o valor teórico (utilizando-se dessas metodologias) e o valor experimental é de apenas 4,05%
Relativistic effects are clorer to up than we think, such as: gold color metal, the operation of lead-acid battery among others. Relativistic effects are more intense in heavy atoms, especially of gold atom, having an essential role for the interpretation of the phenomena of quantum nature, since their effects tend to significantly change the energy and the geometry of the systems. When compared to results obtained by using non-relativistic methods (HF) and quasi-relativistic (ZORA) we can clearly see the influence of the consequences of the theory of relativity, for example, the spinorbit coupling and the breaking of degenerte orbitals. In this work, we will use the relativistic Dirac-Hartree methodologies-Fock (DHF) and Density Functional Theory (DFT) to study systems composed of gold atoms and demonstrate that, despite the high computational cost involved, the relativistic methodologies should be the first option of choise due to excellent quality of the results obtained in geometric and electronic properties such as the bond distance and Electron Afinity. Particularly in the study of molecule Au2 excellent result obtained for the connection distance as the divergence between the theoretical valeu (using these methodologies) and the experimental value is only 4.05%

APA, Harvard, Vancouver, ISO, and other styles

9

Canova, André Luiz Fassone. "Estudo químico quântico relativístico das propriedades eletrônicas e estruturais dos compostos Aun(n=1-5), AuOn-e AuSn - (n=1-2) e AuH /." Bauru, 2014. http://hdl.handle.net/11449/116003.

Full text

Abstract:

Orientador: Aguinaldo Robinson de Souza
Banca: Nelson Henrique Morgon
Banca: Alberico Borges Ferreira da Silva
Banca: Fernando Luis Barroso da Silva
Banca: Alexys Bruno Alfonso
Resumo: Os efeitos relativístico estão mais próximos de nós do que pensamos, com por exemplo: na cor do metal Ouro, no funcionamento da bateria Chumbo-ácido entre outros. Os efeitos relativísticos são mais intensos em átomos pesados, sobretudo no átomo de Ouro, desempenhando um papel essencial para a interpretação dos fenômenos de natureza quântica, visto que os seus efeitos tendem a alterar significativamente a energia e a geometria dos sistemas. Quando comparados aos resultados obtidos pela utilização de metodologias não relativísticas (HF) e quasi relativística (ZORA) podemos perceber claramente a influência das consequências da Teoria da Relatividade, como por exemplo: o acoplamento spin-órbita e a quebra da degenerescência na enrgia dos orbitais. Nesse trabalho, iremos utilizar as metodologias relativísticas de Dirac-Hartree-Fock (DHF) e Teoria do Funcional de Densidade (DFT) para o estudo de sistemas compostos por átomos de Ouro e demonstraremos que, apesar do elevado custo computacional envolvido, as metodologias relativísticas devem ser a primeira opção de escolha dada a excelente qualidade dos resultados obtidos, em propriedades geométricas eletrônicas, tais como: a distância de ligação e Afinidade Eletrônica. Particularmente no estudo da molécula de Au2 obtivemos excelente resultado para a distância de ligação, pois a divergência entre o valor teórico (utilizando-se dessas metodologias) e o valor experimental é de apenas 4,05%
Abstract: Relativistic effects are clorer to up than we think, such as: gold color metal, the operation of lead-acid battery among others. Relativistic effects are more intense in heavy atoms, especially of gold atom, having an essential role for the interpretation of the phenomena of quantum nature, since their effects tend to significantly change the energy and the geometry of the systems. When compared to results obtained by using non-relativistic methods (HF) and quasi-relativistic (ZORA) we can clearly see the influence of the consequences of the theory of relativity, for example, the spinorbit coupling and the breaking of degenerte orbitals. In this work, we will use the relativistic Dirac-Hartree methodologies-Fock (DHF) and Density Functional Theory (DFT) to study systems composed of gold atoms and demonstrate that, despite the high computational cost involved, the relativistic methodologies should be the first option of choise due to excellent quality of the results obtained in geometric and electronic properties such as the bond distance and Electron Afinity. Particularly in the study of molecule Au2 excellent result obtained for the connection distance as the divergence between the theoretical valeu (using these methodologies) and the experimental value is only 4.05%
Doutor

APA, Harvard, Vancouver, ISO, and other styles

10

Nicholson, Melany Isabel Garcia. "Estudo teórico de propriedades estruturais, eletrônicas e redox de monocamadas eletroativas /." Araraquara, 2019. http://hdl.handle.net/11449/183415.

Full text

Abstract:

Orientador: Gustavo Troiano Feliciano
Coorientador: Paulo Roberto Bueno
Banca: Eduardo Maffud Cilli
Banca: Paula Homem de Mello
Resumo: O estudo de monocamadas eletroativas vem ganhando espaço na literatura pois tem se mostrado como uma ferramenta muito promissora para a obtenção de diagnósticos cada vez mais rápidos e precisos para uma grande variedade de condições. Embora o número de publicações sobre o assunto venha aumentando significativamente com o passar dos anos, ainda não existem estudos aprofundados sobre a relação entre a estrutura da monocamada e suas propriedades eletrônicas e redox e como estas influenciam na detecção mais ou menos sensível de moléculas-alvo. Esta dissertação apresenta o estudo teórico das propriedades estruturais, eletrônicas e redox de uma monocamada peptídica com ferroceno terminal preso a uma superfície de ouro. Os cálculos foram feitos numa interface GROMACS-ORCA através da qual se produziram dinâmicas clássicas, quânticas e híbridas (QM/MM). Os resultados obtidos incluem uma comparação de cálculos single point para a estrutura do ferroceno com três bases (6-31G*, DEF2-SVP e DEF2-TZVP) e cinco funcionais (B3LYP, BLYP, BP86, PBE0 e PBE) no qual o conjunto DEF2-TZVP/ BP86 obteve os melhores resultados. A mesma estrutura foi usada para calcular, por meio do QM/MM, a distribuição da energia potencial do ferroceno reduzido e oxidado com a finalidade de produzir curvas de Marcus e analisar se este complexo obedece aos princípios delineados por essa teoria. As curvas mostraram que o ferroceno segue a teoria de Marcus se o meio no qual ele se encontra for homogêneo. Por último, fiz... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The study of electroactive monolayers has been gaining ground in the literature because it has proved to be a very promising tool for obtaining faster and more accurate diagnostics for a wide variety of conditions. Although the number of publications on the subject has increased significantly over the years, there are still no in-depth studies on the relationship between monolayer structure and its redox and electronic properties and how these influence in the sensitivity for detecting target molecules. This dissertation presents the theoretical study of the structural, electronic and redox properties of a peptidic monolayer with ferrocene attached to a gold surface. The calculations were made in a GROMACS-ORCA interface through which classical, quantum and hybrid dynamics (QM/MM) were produced. The results obtained include a comparison of single point calculations for the ferrocene structure with three bases (6-31G*, DEF2-SVP and DEF2-TZVP) and five functional ones (B3LYP, BLYP, BP86, PBE0 and PBE) in which the set DEF2-TZVP/ BP86 got the best results. The same structure was used to calculate the distribution of the potential energy of reduced and oxidized ferrocene by means of the QM / MM in order to produce Marcus curves and to analyze if this complex obeys the principles outlined by this theory. The curves showed that ferrocene follows Marcus's theory if the medium in which it is found is homogeneous. Finally, classical simulations were performed to obtain structural info... (Complete abstract click electronic access below)
Mestre

APA, Harvard, Vancouver, ISO, and other styles

11

Fischer, Michael, Jan Handt, and Rüdiger Schmidt. "Nonadiabatic quantum molecular dynamics with hopping, II. Role of nuclear quantum effects in atomic collisions." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-151796.

Full text

Abstract:

An extension of the nonadiabatic quantum molecular dynamics approach is presented to account for electron-nuclear correlations in the dynamics of atomic many-body systems. The method combines electron dynamics described within time-dependent density-functional or Hartree-Fock theory with trajectory-surface-hopping dynamics for the nuclei, allowing us to take into account explicitly a possible external laser field. As a case study, a model system of H++H collisions is considered where full quantum-mechanical calculations are available for comparison. For this benchmark system the extended surface-hopping scheme exactly reproduces the full quantum results. Future applications are briefly outlined.

APA, Harvard, Vancouver, ISO, and other styles

12

Bischof, Rainer. "Gaussian Critical Line in Anisotropic Mixed Quantum Spin Chains." Doctoral thesis, Universitätsbibliothek Leipzig, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-107225.

Full text

Abstract:

By numerical methods, two models of anisotropic mixed quantum spin chains, consisting of spins of two different sizes, Sa = 1/2 and Sb = 1 as well as Sb = 3/2, are studied with respect to their critical properties at quantum phase transitions in a selected region of parameter space. The quantum spin chains are made up of basecells of four spins, according to the structure Sa − Sa − Sb − Sb. They are described by the XXZ Hamiltonian, that extends the quantum Heisenberg model by a variable anisotropic exchange interaction. As additional control parameter, an alternating exchange constant between nearest-neighbour spins is introduced. Insight gained by complementary application of exact diagonalization and quantum Monte Carlo simulations, as well as appropriate methods of analysis, is embedded in the broad existing knowledge on homogeneous quantum spin chains. In anisotropic homogeneous quantum spin chains, there exist phase boundaries with continuously varying critical exponents, the Gaussian critical lines, along which, in addition to standard scaling relations, further extended scaling relations hold. Reweighting methods, also applied to improved quantum Monte Carlo estimators, and finite-size scaling analysis of simulation data deliver a wealth of numerical results confirming the existence of a Gaussian critical line also in the mixed spin models considered. Extrapolation of exact data offers, apart from confirmation of simulation data, furthermore, insight into the conformal operator content of the model with Sb = 1
Mittels numerischer Methoden werden zwei Modelle anisotroper gemischter Quantenspinketten, bestehend aus Spins zweier unterschiedlicher Größen, Sa = 1/2 und Sb = 1 sowie Sb = 3/2, hinsichtlich ihrer kritischen Eigenschaften an Quanten-Phasenübergängen in einem ausgewählten Parameterbereich untersucht. Die Quantenspinketten sind aus Basiszellen zu vier Spins, gemäß der Struktur Sa − Sa − Sb − Sb, aufgebaut. Sie werden durch den XXZ Hamiltonoperator beschrieben, der das isotrope Quanten-Heisenberg Modell um eine variable anistrope Austauschwechselwirkung erweitert. Als zusätzlicher Kontrollparameter wird eine alterniernde Kopplungskonstante zwischen unmittelbar benachbarten Spins eingeführt. Die durch komplementäre Anwendung exakter Diagonalisierung und Quanten-Monte-Carlo Simulationen, sowie entsprechender Analyseverfahren, gewonnenen Erkenntnisse werden in das umfangreiche existierende Wissen über homogene Quantenspinketten eingebettet. Im Speziellen treten in anisotropen homogenen Quantenspinketten Phasengrenzen mit kontinuierlich variierenden kritischen Exponenten auf, die Gaußschen kritischen Linien, auf denen neben den herkömmlichen auch erweiterte Skalenrelationen Gültigkeit besitzen. Umgewichtungsmethoden, speziell auch angewandt auf verbesserte Quanten-Monte-Carlo Schätzer, und Endlichkeitsskalenanalyse von Simulationsdaten liefern eine Fülle von numerischen Ergebnissen, die das Auftreten der Gaußschen kritischen Linie auch in den untersuchten gemischten Quantenspinketten bestätigen. Die Extrapolation exakter Daten bietet, neben der Bestätigung der Simulationsdaten, darüber hinaus Einblick in einen Teil des konformen Operatorinhalts des Modells mit Sb = 1

APA, Harvard, Vancouver, ISO, and other styles

13

Di, Martino Giuliana. "Quantum plasmonics : from quantum statistics to quantum interferences." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/24543.

Full text

Abstract:

In this thesis, we focus our attention on the excitation of Surface Plasmon Polaritons (SPPs) and their propagation along metal stripes. Plasmons are characterized by losses into the metal, therefore an important step is to investigate the effect of these losses on their quantum properties. This is a field not yet fully investigated and the work presented here will give us the possibility to understand the effect of losses on the plasmons quantum properties. This will allow us to prove that plasmons can be used in the quantum information technology field, since they keep the quantum information regardless of their lossy character. Another key property yet to be fully investigated is the bosonic character of single surface plasmon polaritons (SPPs). The quasi-particle nature of SPPs, consisting of a photon (boson) coupled to a charge density wave of electrons (fermions), makes them an unusual type of quantum excitation. It is, as of yet, unclear whether SPPs are bosons, fermions, or a hybrid mixture. Here, we will prove the bosonic character of plasmons, making use of interference experiments. This study will open opportunities for controlling quantum states of light in ultra-compact nanophotonic plasmonic circuitry. First of all, the mean excitation rates, intensity correlations and Fock state populations are studied by using heralded single photons generated via spontaneous parametric down conversion as sources of light. One downconverted beam is used as a trigger, the other one is the signal we send to the metal stripes to excite the plasmons. After an introduction on the meaning of coherence functions, we explain how we couple photons into a gold waveguide with gratings on both sides, where the coupled plasmon is confined at the interface between gold and air. By measuring the second-order quantum coherence function g2(t), we demonstrated the ability to excite single SPPs. Moreover, the effect of losses incurred during propagation of the single SPPs is consistent with the classical exponential behaviour and does not change the value of g2(t), providing evidence that a linear uncorrelated Markovian loss model is valid for SPP damping at the single quanta level. Then, we move onto more complicated devices, such as X-shaped stripes that act as a plasmonic beamsplitter, in order to observe nonclassical effects in the interference of two single plasmons. This is an important step along the way to understanding better the behaviour of single surface plasmons at the quantum level and how one can build more complicated quantum interference networks, such as plasmonic-based quantum logic gates. In order to fully verify the bosonic nature of single excitations in the quantum regime it is vital to observe quantum interference. A natural thing to probe in the most basic type of scatterer (a 50/50 beamsplitter) operating in the quantum regime, is how it acts on two separate single surface plasmons. Here the launching method is the same as for the previous experiment, except that the waveguide structure is in the form of a 50/50 beamsplitter (X-shape) and both photons from the parametric down-conversion type-I generation are sent onto the two inputs of the plasmonic beamsplitter. By this way, both the beams, generated by the nonlinear crystal, act as signal beams. If the SPPs are truly bosonic and indistinguishable then they tend to bunch together when they interact at the beamsplitter -this is the well known Hong-Ou and Mandel quantum interference effect. In this work we report the first direct observation of quantum interference in the HOM effect for single SPPs, demonstrating by this way the bosonic nature of plasmons.

APA, Harvard, Vancouver, ISO, and other styles

14

Erker, Paul. "Physics and information. What is the role of information in physics?" Doctoral thesis, Universitat Autònoma de Barcelona, 2019. http://hdl.handle.net/10803/666901.

Full text

Abstract:

Fa més d'un segle els físics de tot el món desenvolupaven una teoria per descriure comportaments estranys recentment descobertes d'alguns sistemes físics, això marca el naixement de la Teoria Quàntica. Algunes dècades més tard, la idea revolucionària de separar la informació de la seva companyia física va conduir a l'establiment de la Teoria de la Informació. Aquests al principi es van unir les teories independents en les últimes dècades del segle anterior deixant-nos de Teoria de la Informació Quàntica. Aquesta tesi explorarà una intersecció entre matemàtiques, física i informàtica, tractant d'aclarir l'entrellaçat de l'anterior. Tot seguit, es van establir els resultats que es van establir durant els anys d'estudis que van dur a aquest treball. La pregunta plantejada en el títol no es respondrà plenament ja que pot ser massa aviat per donar una resposta definitiva a aquesta àmplia pregunta.
Hace más de un siglo, los físicos de todo el mundo estaban desarrollando una teoría para describir comportamientos extraños recientemente descubiertos de algunos sistemas físicos, lo que marca el nacimiento de la teoría cuántica. Algunas décadas más tarde, la idea innovadora de separar la información de su portador físico llevó al establecimiento de la teoría de la información. Estas teorías independientes al principio se fusionaron en las últimas décadas del siglo anterior, dando lugar a la teoría de la información cuántica. Esta tesis explorará temas en la intersección entre matemáticas, física y ciencias de la computación, tratando de dilucidar la interconexión entre las tres. Dicha exploración se llevará a cabo junto con la presentación de los resultados obtenidos durante estos años de estudio. La pregunta planteada en el título no será respondida completamente, ya que puede ser demasiado pronto para dar una respuesta definitiva a esta amplia pregunta.
More than a century ago, physicists around the world were collectively developing a theory to describe the newly discovered strange behaviours of some physical systems. This marks the birth of quantum theory. Few decades later, the groundbreaking idea to separate information from its physical carrier led to the establishment of information theory. These, initially independent theories, merged together in the last decades of the former century, leaving us with quantum information theory. This thesis will explore topics at the intersection of mathematics, physics and computer science, trying to elucidate the interwovenness of these three disciplines. While doing so, the results that were established during the years of studies leading up to this work are introduced. The question posed in the title will not be answered fully, as it may be too early still to give a definite answer to this multifaceted question.

APA, Harvard, Vancouver, ISO, and other styles

15

Pozas, Kerstjens Alejandro. "Quantum information outside quantum information." Doctoral thesis, Universitat Politècnica de Catalunya, 2019. http://hdl.handle.net/10803/667696.

Full text

Abstract:

Quantum theory, as counter-intuitive as a theory can get, has turned out to make predictions of the physical world that match observations so precisely that it has been described as the most accurate physical theory ever devised. Viewing quantum entanglement, superposition and interference not as undesirable necessities but as interesting resources paved the way to the development of quantum information science. This area studies the processing, transmission and storage of information when one accounts that information is physical and subjected to the laws of nature that govern the systems it is encoded in. The development of the consequences of this idea, along with the great advances experienced in the control of individual quantum systems, has led to what is now known as the second quantum revolution, in which quantum information science has emerged as a fully-grown field. As such, ideas and tools developed within the framework of quantum information theory begin to permeate to other fields of research. This Ph.D. dissertation is devoted to the use of concepts and methods akin to the field of quantum information science in other areas of research. In the same way, it also considers how encoding information in quantum degrees of freedom may allow further development of well-established research fields and industries. This is, this thesis aims to the study of quantum information outside the field of quantum information. Four different areas are visited. A first question posed is that of the role of quantum information in quantum field theory, with a focus in the quantum vacuum. It is known that the quantum vacuum contains entanglement, but it remains unknown whether it can be accessed and exploited in experiments. We give crucial steps in this direction by studying the extraction of vacuum entanglement in realistic models of light-matter interaction, and by giving strict mathematical conditions of general applicability that must be fulfilled for extraction to be possible at all. Another field where quantum information methods can offer great insight is in that of quantum thermodynamics, where the idealizations made in macroscopic thermodynamics break down. Making use of a quintessential framework of quantum information and quantum optics, we study the cyclic operation of a microscopic heat engine composed by a single particle reciprocating between two finite-size baths, focusing on the consequences of the removal of the macroscopic idealizations. One more step down the stairs to applications in society, we analyze the impact that encoding information in quantum systems and processing it in quantum computers may have in the field of machine learning. A great desideratum in this area, largely obstructed by computational power, is that of explainable models which not only make predictions but also provide information about the decision process that triggers them. We develop an algorithm to train neural networks using explainable techniques that exploits entanglement and superposition to execute efficiently in quantum computers, in contrast with classical counterparts. Furthermore, we run it in state-of-the-art quantum computers with the aim of assessing the viability of realistic implementations. Lastly, and encompassing all the above, we explore the notion of causality in quantum mechanics from an information-theoretic point of view. While it is known since the work of John S. Bell in 1964 that, for a same causal pattern, quantum systems can generate correlations between variables that are impossible to obtain employing only classical systems, there is an important lack of tools to study complex causal effects whenever a quantum behavior is expected. We fill this gap by providing general methods for the characterization of the quantum correlations achievable in complex causal patterns. Closing the circle, we make use of these tools to find phenomena of fundamental and experimental relevance back in quantum information.
La teoría cuántica, la más extraña y antiintuitiva de las teorías físicas, es también considerada como la teoría más precisa jamás desarrollada. La interpretación del entrelazamiento, la superposición y la interferencia como interesantes recursos aprovechables cimentó el desarrollo de la teoría cuántica de la información (QIT), que estudia el procesado, transmisión y almacenamiento de información teniendo en cuenta que ésta es física, en tanto a que está sujeta a las leyes de la naturaleza que gobiernan los sistemas en que se codifica. El desarrollo de esta idea, en conjunción con los recientes avances en el control de sistemas cuánticos individuales, ha dado lugar a la conocida como segunda revolución cuántica, en la cual la QIT ha emergido como un área de estudio con denominación propia. A consecuencia de su desarrollo actual, ideas y herramientas creadas en su seno comienzan a permear a otros ámbitos de investigación. Esta tesis doctoral está dedicada a la utilización de conceptos y métodos originales del campo de información cuántica en otras áreas. También considera cómo la codificación de información en grados de libertad cuánticos puede afectar el futuro desarrollo de áreas de investigación e industrias bien establecidas. Es decir, esta tesis tiene como objetivo el estudio de la información cuántica fuera de la información cuántica, haciendo hincapié en cuatro ámbitos diferentes. Una primera cuestión propuesta es la del papel de la información cuántica en la teoría cuántica de campos, con especial énfasis en el vacío cuántico. Es conocido que el vacío cuántico contiene entrelazamiento, pero aún se desconoce éste es accesible para su uso en realizaciones experimentales. En esta tesis se dan pasos cruciales en esta dirección mediante el estudio de la extracción de entrelazamiento en modelos realistas de la interacción materia-radiación, y dando condiciones matemáticas estrictas que deben ser satisfechas para que dicha extracción sea posible. Otro campo en el cual métodos propios de QIT pueden ofrecer nuevos puntos de vista es en termodinámica cuántica. A través del uso de un marco de trabajo ampliamente utilizado en información y óptica cuánticas, estudiamos la operación cíclica de un motor térmico microscópico que alterna entre dos baños térmicos de tamaño finito, prestando especial atención a las consecuencias de la eliminación de las idealizaciones macroscópicas utilizadas en termodinámica macroscópica. Acercándonos a aplicaciones industriales, analizamos el potencial impacto de codificar y procesar información en sistemas cuánticos en el ámbito del aprendizaje automático. Un fin codiciado en esta área, inaccesible debido a su coste computacional, es el de modelos explicativos que realicen predicciones, y además ofrezcan información acerca del proceso de decisión que las genera. Presentamos un algoritmo de entrenamiento de redes neuronales con técnicas explicativas que hace uso del entrelazamiento y la superposición para tener una ejecución eficiente en ordenadores cuánticos, en comparación con homólogos clásicos. Además, ejecutamos el algoritmo en ordenadores cuánticos contemporáneos con el objetivo de evaluar la viabilidad de implementaciones realistas. Finalmente, y englobando todo lo anterior, exploramos la noción de causalidad en mecánica cuántica desde el punto de vista de la teoría de la información. A pesar de que es conocido que para un mismo patrón causal existen sistemas cuánticos que dan lugar a correlaciones imposibles de generar por mediación de sistemas clásicos, existe una notable falta de herramientas para estudiar efectos causales cuánticos complejos. Cubrimos esta falta mediante métodos generales para la caracterización de las correlaciones cuánticas que pueden ser generadas en estructuras causales complejas. Cerrando el círculo, usamos estas herramientas para encontrar fenómenos de relevancia fundamental y experimental en la información cuántica

APA, Harvard, Vancouver, ISO, and other styles

16

Makarov, Vadim. "Quantum cryptography and quantum cryptanalysis." Doctoral thesis, Norwegian University of Science and Technology, Faculty of Information Technology, Mathematics and Electrical Engineering, 2007. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-1473.

Full text

Abstract:

This doctoral thesis summarizes research in quantum cryptography done at the Department of Electronics and Telecommunications at the Norwegian University of Science and Technology (NTNU) from 1998 through 2007.

The opening parts contain a brief introduction into quantum cryptography as well as an overview of all existing single photon detection techniques for visible and near infrared light. Then, our implementation of a fiber optic quantum key distribution (QKD) system is described. We employ a one-way phase coding scheme with a 1310 nm attenuated laser source and a polarization-maintaining Mach-Zehnder interferometer. A feature of our scheme is that it tracks phase drift in the interferometer at the single photon level instead of employing hardware phase control measures. An optimal phase tracking algorithm has been developed, implemented and tested. Phase tracking accuracy of +-10 degrees is achieved when approximately 200 photon counts are collected in each cycle of adjustment. Another feature of our QKD system is that it uses a single photon detector based on a germanium avalanche photodiode gated at 20 MHz. To make possible this relatively high gating rate, we have developed, implemented and tested an afterpulse blocking technique, when a number of gating pulses is blocked after each registered avalanche. This technique allows to increase the key generation rate nearly proportionally to the increase of the gating rate. QKD has been demonstrated in the laboratory setting with only a very limited success: by the time of the thesis completion we had malfunctioning components in the setup, and the quantum bit error rate remained unstable with its lowest registered value of about 4%.

More than half of the thesis is devoted to various security aspects of QKD. We have studied several attacks that exploit component imperfections and loopholes in optical schemes. In a large pulse attack, settings of modulators inside Alice's and Bob's setups are read out by external interrogating light pulses, without interacting with quantum states and without raising security alarms. An external measurement of phase shift at Alice's phase modulator in our setup has been demonstrated experimentally. In a faked states attack, Eve intercepts Alice's qubits and then utilizes various optical imperfections in Bob's scheme to construct and resend light pulses in such a way that Bob does not distinguish his detection results from normal, whereas they give Bob the basis and bit value chosen at Eve's discretion. Construction of such faked states using several different imperfections is discussed. Also, we sketch a practical workflow of breaking into a running quantum cryptolink for the two abovementioned classes of attacks. A special attention is paid to a common imperfection when sensitivity of Bob's two detectors relative to one another can be controlled by Eve via an external parameter, for example via the timing of the incoming pulse. This imperfection is illustrated by measurements on two different single photon detectors. Quantitative results for a faked states attack on the Bennett-Brassard 1984 (BB84) and the Scarani-Acin-Ribordy-Gisin 2004 (SARG04) protocols using this imperfection are obtained. It is shown how faked states can in principle be constructed for quantum cryptosystems that use a phase-time encoding, the differential phase shift keying (DPSK) and the Ekert protocols. Furthermore we have attempted to integrate this imperfection of detectors into the general security proof for the BB84 protocol. For all attacks, their applicability to and implications for various known QKD schemes are considered, and countermeasures against the attacks are proposed.

The thesis incorporates published papers [J. Mod. Opt. 48, 2023 (2001)], [Appl. Opt. 43, 4385 (2004)], [J. Mod. Opt. 52, 691 (2005)], [Phys. Rev. A 74, 022313 (2006)], and [quant-ph/0702262].

APA, Harvard, Vancouver, ISO, and other styles

17

Delbecque, Yannick. "Quantum games as quantum types." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=40670.

Full text

Abstract:

In this thesis, we present a new model for higher-order quantum programming languages. The proposed model is an adaptation of the probabilistic game semantics developed by Danos and Harmer: we expand it with quantum strategies which enable one to represent quantum states and quantum operations. Some of the basic properties of these strategies are established and then used to construct denotational semantics for three quantum programming languages. The first of these languages is a formalisation of the measurement calculus proposed by Danos et al. The other two are new: they are higher-order quantum programming languages. Previous attempts to define a denotational semantics for higher-order quantum programming languages have failed. We identify some of the key reasons for this and base the design of our higher-order languages on these observations. The game semantics proposed in this thesis is the first denotational semantics for a lambda-calculus equipped with quantum types and with extra operations which allow one to program quantum algorithms. The results presented validate the two different approaches used in the design of these two new higher-order languages: a first one where quantum states are used through references and a second one where they are introduced as constants in the language. The quantum strategies presented in this thesis allow one to understand the constraints that must be imposed on quantum type systems with higher-order types. The most significant constraint is the fact that abstraction over part of the tensor product of many unknown quantum states must not be allowed. Quantum strategies are a new mathematical model which describes the interaction between classical and quantum data using system-environment dialogues. The interactions between the different parts of a quantum system are described using the rich structure generated by composition of strategies. This approach has enough generality to be put in relation with other work in qu
Nous présentons dans cette thèse un nouveau modèlepour les langages de programmation quantique. Notre modèle est uneadaptation de la sémantique de jeux probabilistes définie par Danos etHarmer: nous y ajoutons des stratégies quantiquespour permettre la représentation des états et des opérations quantiques.Nous établissons quelques propriétés de base de ces stratégies. Cespropriétés sont ensuite utilisées pour construire des sémantiquesdénotationnelles pour trois langages de programmation quantique. Le premierlangage est une formalisation du calcul par mesures proposé par Danoset al. Les deux autres langages sont nouveaux: ce sont deslangages quantiques d'ordre supérieur dont la syntaxe a été construiteà partir d'observations expliquant l'échec des tentatives précédentespour construire une sémantique dénotationnelle pour de tels langages. La sémantique de jeux présentée dans cette thèseest la première sémantique dénotationnelle pour de telslambda-calculs équipés de types et d'opérations supplémentairespermettant la programmation d'algorithmes quantiques. Les résultatsprésentés valident les deux approches différentes utilitées dans laconception de ces deux nouveaux languages d'ordre supérieur: une premièreoù les états quantiques sont indirectement accessibles via desréférences et une seconde où ils sont introduit directement comme desconstantes dans le langage. Les stratégies quantiques présentéespermettent de comprendre les contraintes devant êtreimposées aux systèmes de type quantique comportant des types d'ordresupérieurs. La contrainte la plus importante est le fait que l'abstractionsur une partie d'un état quantique comportant plusieurs qbits inconnus doitêtre prohibée. Les stratégies quantiques constituent un nouveau modèle mathématique quidécrit l'interaction entre les données classiques et quantiques par desdialogues entre système et environnement. L'interaction entre les differentespar

APA, Harvard, Vancouver, ISO, and other styles

18

Clark, Lewis Alexander. "Quantum feedback for quantum technology." Thesis, University of Leeds, 2017. http://etheses.whiterose.ac.uk/18485/.

Full text

Abstract:

It is widely believed that quantum physics is a fundamental theory describing the Universe. As such, one would expect to be able to see how classical physics that is observed in the macroscopic world emerges from quantum theory. This has so far largely eluded physicists, due to the inherent linear nature of quantum physics and the non-linear behaviour of classical physics. One of the principle differences between classical and quantum physics is the statistical, probabilistic nature of quantum theory. It is from this property that non-classical states can arise, such as entangled states. These states possess maximal correlations. However, they are not the only way in which correlations are created in quantum systems. This thesis aims to show how open quantum systems naturally contain correlations from their quantum nature. Moreover, even seemingly simple open quantum systems can behave far more complexly than expected upon the introduction of quantum feedback. Using this effect, the dynamics may become non-linear and as such behave non-trivially. Furthermore, it is shown how these effects may be exploited for a variety of tasks, including a computational application in hidden quantum Markov models and a quantum metrology scheme that does not require the use of exotic quantum states. This results in the design of systems that benefit from the use of quantum mechanics, but are not constrained by the use of experimentally difficulties such as entanglement.

APA, Harvard, Vancouver, ISO, and other styles

19

Dale, Howard. "Quantum coins and quantum sampling." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/49203.

Full text

Abstract:

Quantum computing is rapidly becoming one of the largest research areas in quantum physics and yet we are still unable to prove the superiority of quantum computing over classical with the exception of a few contrived and unrealistic scenarios. Understanding the areas in which quantum computing provides an advantage and, more importantly, where that advantage comes from is the key to making progress in the field. We certainly do not solve this mystery in this thesis but do explore some unconventional routes through which answers may be found in the future. To this end we explore quantum advantage in a different computational setting. Rather than working with Turing Machines as most research does, we focus on the Bernoulli Factory: a randomness processing scheme studied in the fields of statistics and computer science. The Bernoulli Factory takes an infinite string of random bits generated with a fixed unknown bias as input and outputs a single random bit, the bias of which is a function of the input bias. This can be seen more intuitively as generating one biased coin from another, given a desired relationship between the two biases. The Bernoulli Factory is inherently probabilistic, like quantum mechanics, and so, it leads us to questions about the fundamental nature of quantum randomness and quantum sampling. We find, as we hoped, that the Bernoulli Factory is more tractable than the Turing Machine and that we are able to prove quantum superiority in both resource efficiency and classes of computable functions. We first give the quantum analogue of the classical Keane-O'’Brien theorem which establishes the increased class of computable functions for the quantum case. We then adjust the problem in a variety of ways, such as introducing multiple coins, errors in state preparation, phases and restriction on the bias or operations allowed. These lead to additional results which lend insight into the problems faced in quantum computing as well as the nature of quantum randomness.

APA, Harvard, Vancouver, ISO, and other styles

20

Abeyratne, Sumana. "QUANTUM STRATEGIES AND QUANTUM GAMBLING." Bowling Green State University / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1150470447.

Full text

APA, Harvard, Vancouver, ISO, and other styles

21

Barr, Katherine Elizabeth. "Quantum walks and quantum computation." Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/4975/.

Full text

Abstract:

The field of quantum information applies the concepts of quantum physics to problems in computer science, and shows great potential for allowing efficient computation. In this thesis I concentrate on a particular quantum information theoretic tool known as the quantum walk. There are two widely studied versions of the quantum walk, the continuous time walk, and the discrete time walk. The discrete time walk is particularly amenable to investigation using numerical methods, from which most of the results in this thesis are derived, and is the main focus of the work presented. Two aspects of the discrete time walk are investigated: their transport properties and their interpretation as quantum computers. I investigated the transport properties in two ways, by looking for a particular type of transport known as perfect state transfer, and examining the transport properties of a new type of coin operator. The search for perfect state transfer concentrated on modifications of small cycles. I found that perfect state transfer is rare for the choices of coin operators tested. The structures tested for perfect state transfer were based on cycles, and it appears that the type of modification has more of an effect than the size of the cycle. This makes intuitive sense, as the modifications found to lead to walks exhibiting perfect state transfer affected only the initial and target node of the cycle. I then investigated a new type of coin operator which does not allow amplitude to return to the node it has come from. This effectively simulates a dimer. Using the general form of this type of operator and random variables for each parameter, I found that the expected distance of the walker from the origin, and standard deviation, were independent of the initial condition. The second half of the thesis concentrates on computational applications of quantum walks using the language acceptance model. I first note their equivalence to a type of quantum automaton known as the QFA-WOM, and this provides an intuitive understanding of the role of the WOM. I then use a more direct construction to show that they can accept a range of formal languages. Using this construction allows us to use superpositions of words as inputs, and the insights provided by investigating these suggest a new way of approaching the problem of quantum state discrimination.

APA, Harvard, Vancouver, ISO, and other styles

22

Santos, Mateus de Araujo. "Quantum realism and quantum surrealism." Universidade Federal de Minas Gerais, 2012. http://hdl.handle.net/1843/BUOS-8XVM55.

Full text

Abstract:

In this thesis we explore the question: whats strange about quantum mechanics? This exploration is divided in two parts: in the first, we prove that there is in fact something strange about quantum mechanics, by showing that it is not possible to conciliate quantum theory with various different definitions of what should be a normal theory, that is, a theory that respects our classical intuition. In the second part, our objective is to describe precisely which parts of quantum mechanics are non-classical. For that, we define a classical theory as a noncontextual ontological theory, and the non-classical parts of quantum mechanics as being the probability distributions that a ontological noncontextual theory cannot reproduce. Exploring this formalism, we find a new family of inequalities that characterize non-classicality.
Nessa dissertação exploramos a questão: o que há de estranho em mecânica quântica? Essa exploração se divide em duas partes: na primeira, provamos que de fato há algo estranho em mecânica quântica, mostrando que não é possível conciliar o formalismo quântico com várias definições diferentes do que seria uma teoria normal, isto é, que respeite nossa intuição clássica sobre o mundo. Na segunda parte, nosso objetivo é descrever precisamente quais partes da mecânica quântica são não-clássicas. Para isso, definimos uma teoria clássica como uma teoria ontológica não-contextual, e as partes nãoclássicas da mecânica quântica como sendo as distribuições de probabilidade que uma teoria ontológica não-contextual não consegue reproduzir. Explorando esse formalismo, encontramos uma nova família de desigualdades que caracterizam essa não-classicalidade.

APA, Harvard, Vancouver, ISO, and other styles

23

Wardrop, Matthew Phillip. "Quantum Gates for Quantum Dots." Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/14938.

Full text

Abstract:

Since the mid-20th century it has been understood that a general-purpose quan- tum computer would be able to efficiently solve problems that will forever be out-of-reach for conventional computers. Since then, many quantum algorithms have been developed with applications in a wide range of domains including cryptography, simulations, machine learning and data analysis. While this has resulted in substantial attention being paid to the development of quantum com- puters, the best architectures to use in their fabrication is not yet clear. Semiconductor quantum dot devices are a particularly promising candidate for use in quantum computing architectures, as it is anticipated that once the funda- mental building blocks are implemented, they might be massively scalable using the existing lithography techniques of the semiconductor industry. So far, how- ever, it is not yet clear how best to implement the high-fidelity gates required for general-purpose quantum computation. In this thesis, we present and characterise novel theoretical proposals for fast, simple and high-fidelity two-qubit gates using magnetic (exchange) coupling for specific semiconductor quantum dot qubits; namely, the singlet-triplet and resonant-exchange qubits. These two-qubit operations are simple enough that it is feasible for them to be implemented in experiments of the near future. Success- ful implementations would significantly extend the experimentally demonstrable frontier of semi-conductor quantum dot devices as relevant to their use in uni- versal quantum computing architectures. We also develop simple parameter estimation schemes by which it is possible to substantially mitigate the dominant sources of error for our proposed gates; namely, low-frequency charge and magnetic noise. We develop the techniques in the context of pseudo-static magnetic field gradient fluctuations in singlet- triplet qubits, and demonstrate that these techniques lead to a several orders of magnitude improvement in single-qubit coherence times. With minimal effort this could be ported to other qubit architectures.

APA, Harvard, Vancouver, ISO, and other styles

24

McCutcheon, William Dundee. "On the measurement of quantum states : quantum photonics for quantum information." Thesis, University of Bristol, 2017. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.730869.

Full text

APA, Harvard, Vancouver, ISO, and other styles

25

Valentini, Lorenzo. "Quantum Error Correction for Quantum Networks." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.

Find full text

Abstract:

Le quantum networks e molte altre tecnologie, quali i quantum computer, necessitano di qubit affidabili per il loro funzionamento. Per ottenere ciò, in questo elaborato, si presenta il tema della quantum error correction ponendo particolare attenzione ai codici quantum low-density parity-check (QLDPC). In aggiunta, vengono testati alcuni algoritmi su IBMQ, la serie di computer quantistici resi disponibili online da IBM, per comprenderne le problematiche. Si conclude l'elaborato con alcune riflessioni su come i codici presentati possono arginare alcune delle problematiche riscontrate durante l'implementazione su quantum computer.

APA, Harvard, Vancouver, ISO, and other styles

26

Guerini, de Souza Leonardo. "Simulating quantum measurements and quantum correlations." Doctoral thesis, Universitat Politècnica de Catalunya, 2018. http://hdl.handle.net/10803/482108.

Full text

Abstract:

This PhD thesis is focused on the quantum measurement simulability problem, that is, deciding whether a given measurement can be simulated when only a restricted subset of measurements is accessible. We provide an operational framework for this problem based on classical manipulations over the set of simulators. Particular cases of interest are further investigated, in which the simulators are taken to be projective measurements, measurements of a fixed number of outcomes, and arbitrary sets of fixed cardinality. In each of these situations we derive either necessary or sufficient conditions for simulability, and full characterisations in terms of semidefinite programming for some specific cases. Since joint measurability is a particular case of simulability, we also present a natural generalisation for it. Besides deciding whether a given measurement is simulable by some set of simulators, we also pose the question of what are the most robust measurements against simulability. We provide a strategy for approximating the set of quantum measurements based on relaxing the positivity constraint. This allows us to identify the most robust qubit measurement in terms of projective simulability, as well as the most incompatible sets of N measurements, for N = 1, . . . , 5, which notably are found to be always projective. By applying our simulability results in the context of Einstein-Podolsky-Rosen steering and Bell nonlocality we are able to construct improved and more general local models. Starting from models for a finite number of measurements we obtain the first general method for constructing local models for arbitrary families of quantum states. Similarly, our study on projective simulability yields a strategy for extending models for projective measurements to arbitrary ones, culminating in the most efficient local model for two-qubit Werner states and general measurements
Esta tese de doutorado é centrada no problema de simulação de medições quânticas, ou seja, em decidir se uma dada medição pode ser simulada quando temos acesso a apenas um subconjunto restrito de medições. Apresentamos um framework operacional para esse problema, baseado em manipulações clássicas sobre o conjunto de simuladores. Casos particulares de interesse são estudados em detalhe, nos quais o conjunto de simuladores é dado por medições projetivas, medições de um número fixo de outcomes, e conjuntos arbitrários de cardinalidade fixada. Em cada uma dessas situações, derivamos condições necessárias ou suficientes para simulabilidade, e uma caracterização completa em termos de programação semidefinida em alguns casos específicos. Como comensurabilidade é um caso particular de simulabilidade, apresentamos também uma generalização natural para esse conceito. Além de decidir se uma dada medição é simulável ou não, também exploramos a questão de quais são as medições mais robustas contra simulabilidade. Apresentamos então uma estratégia para aproximar o conjunto das medições quânticas baseada em uma relaxação da condição de positividade. Isso nos permite identificar a medição mais robusta contra simulabilidade projetiva em dimensão 2, assim como os conjuntos de N medições mais incompatíveis, para N = 1, . . . , 5, que notavelmente se revelam ser projetivas em todos esses casos. Aplicando nossos resultados de simulabilidade no contexto de Einstein-Podolsky-Rosen steering e não-localidade de Bell, somos capazes de construir modelos locais melhores e mais gerais. Partindo de modelos para um número finito de medições, obtemos o primeiro método geral para construção de modelos locais para famílias arbitrárias de estados quânticos. De forma similar, nosso estudo de simulabilidade projetiva fornece uma estratégia para estender modelos locais para medições projetivas a medições arbitrárias, culminando no mais eficiente modelo local para estados de Werner de dois qubits e medições quaisquer
Aquesta tesi doctoral se centra en el problema de la simulació de mesures quàntiques, és a dir, en decidir si es pot simular una determinada mesura quan només tenim accés a un subconjunt restringit de mesures diferents. Presentem un marc operacional per a aquest problema, basat en manipulacions clàssiques sobre el conjunt de simuladors. Casos particulars d’interès son estudiat en detall, on el conjunt de simuladors està donat per mesures projectius, mesures d’un nombre fix de resultats i conjunts arbitraris de cardinalitat fixa. En cadascuna d’aquestes situacions, derivem condicions necessaris o suficients per a la simulació, i una caracterització completa en termes de programació semi-definida en alguns casos específics. Com la mensurabilitat conjunta és un cas particular de simulació, presentem també una generalització natural per a aquest concepte. A més de decidir si un mesura és simulable o no, també exploram la qüestió de quines son las mesures més robustes contra la simulabilitat. A continuació, presentem una estratègia per aproximar el conjunt de mesures quàntiques basat en una relaxació de la condició de positivitat. Això permet la identificació de la mesura més robusta envers la simulació projectiva en dimensió 2, així com els conjunts més incompatibles de N mesures, per N = 1, . . . , 5, que notablement resulten ser projectivas en tots aquests casos. Aplicant els nostres resultats de simulació en el context d’Einstein-Podolsky-Rosen steering i no-localitat de Bell, som capaços de construir models locals millors i més generals. A partir de models per a un nombre finit de mesures, obtenim el primer mètode general per a la construcció de models locals per a famílies arbitràries d’estats quàntics. De la mateixa manera, el nostre estudi de la simulació projectiva proporciona una estratégia per ampliar models locals per a mesures projectivas a mesures arbitraris, culminant en el model local més eficient per als estats de Werner de dos qubits i mesures generals

APA, Harvard, Vancouver, ISO, and other styles

27

Allcock, Jonathan. "Quantum non-locality and quantum communication." Thesis, University of Bristol, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.521062.

Full text

APA, Harvard, Vancouver, ISO, and other styles

28

Weilenmann, Mirjam. "Quantum causal structure and quantum thermodynamics." Thesis, University of York, 2017. http://etheses.whiterose.ac.uk/19454/.

Full text

Abstract:

This thesis reports progress in two domains, namely causal structures and microscopic thermodynamics, both of which are highly pertinent in the development of quantum technologies. Causal structures fundamentally influence the development of protocols for quantum cryptography and microscopic thermodynamics is crucial for the design of quantum computers. The first part is dedicated to the analysis of causal structure, which encodes the relationship between observed variables, in general restricting the set of possible correlations between them. Our considerations rely on a recent entropy vector method, which we first review. We then develop new techniques for deriving entropic constraints to differentiate between causal structures. We provide sufficient conditions for entropy vectors to be realisable within a causal structure and derive new, improved necessary conditions in terms of so-called non-Shannon inequalities. We also report that for a family of causal structures, including the bipartite Bell scenario and the bilocal causal structure, entropy vectors are unable to distinguish between classical and quantum causes, in spite of the existence of quantum correlations that are not classically reproducible. Hence, further development is needed in order to understand cause from a quantum perspective. In the second part we explore an axiomatic framework for modelling error-tolerant processes in microscopic thermodynamics. Our axiomatisation allows for the accommodation of finite precision levels, which is crucial for describing experiments in the microscopic regime. Moreover, it is general enough to permit the consideration of different error types. The framework leads to the emergence of manageable quantities that give insights into the feasibility and expenditure of processes, which for adiabatic processes are shown to be smooth entropy measures. Our framework also leads to thermodynamic behaviour at the macroscopic scale, meaning that for thermodynamic equilibrium states a unique function provides necessary and sufficient conditions for state transformations, like in the traditional second law.

APA, Harvard, Vancouver, ISO, and other styles

29

Lan, Zhihao. "Quantum simulations with ultracold quantum gases." Thesis, Heriot-Watt University, 2012. http://hdl.handle.net/10399/2581.

Full text

Abstract:

This thesis explores Feynman’s idea of quantum simulations by using ultracold quantum gases. In the first part of the thesis we develop a general method applicable to atoms or molecules or even nanoparticles, to decelerate a hot fast gas beam to zero velocity by using an optical cavity. This deceleration method is based on a novel phase stability mechanism in the bad cavity regime, which is very different from the traditional cavity cooling studies where a good cavity is needed. We propose several schemes to decelerate the gas beam based on this new phase stability mechanism. Practical issues for realizing the proposals are also discussed in detail which show that the deceleration schemes are feasible using present experimental techniques. In the second part of this thesis, we show how the concept of quantum simulations is applied to multiple-layered Dirac cones and related phenomena by using multi-component ultracold fermionic atoms in optical lattices where the spin-dependent hopping and on-site spin flipping are both controlled by Raman lasers. By tuning the spin-dependent hopping according to the representations of su(2) algebra, we show that we can simulate the Dirac-Weyl fermions with any arbitrary spin beyond the spin ½ cases found in graphene and topological insulators. These high spin Dirac-Weyl fermions show rich anomalous quantum Hall effects and a remarkable Klein multi-refringent tunnelling. Moreover, when getting rid of the limitations of su(2) algebra and allowing for on-site spin flipping, we further investigate Modified Dispersion Relations (MDRs) and Neutrino Oscillations (NOs) as in Standard Model Extensions (SMEs) by virtue of an analogue between the three-family fermions in particle physics and a three-layered Dirac cones scheme. This thesis shows the important role ultracold quantum gases play in quantum simulations to address some of the most challenging topics in modern physics.

APA, Harvard, Vancouver, ISO, and other styles

30

Oeckl, Robert. "Quantum geometry and Quantum Field Theory." Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621912.

Full text

APA, Harvard, Vancouver, ISO, and other styles

31

Garrido, Mauricio. "Quantum Optics in Coupled Quantum Dots." Ohio University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1273589966.

Full text

APA, Harvard, Vancouver, ISO, and other styles

32

Liu, Zi-Wen. "On quantum randomness and quantum resources." Thesis, Massachusetts Institute of Technology, 2018. https://hdl.handle.net/1721.1/122846.

Full text

Abstract:

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2018
Cataloged from PDF version of thesis.
Includes bibliographical references.
This thesis is consisted of two independent parts. The first part is on entanglement, quantum randomness, and complexity beyond scrambling. More explicitly, we study the Rényi entanglement entropies of quantum designs. The results lay the mathematical foundation for studying the hierarchy of complexities in between scrambling and Haar randomness by entanglement. The second part explores the general aspects of quantum resource theory. We introduce three theories that do not rely on the specific resource: the theory of resource destroying maps, the one-shot operational resource theory, and the resource theory of quantum channels.
by Zi-Wen Liu.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Physics

APA, Harvard, Vancouver, ISO, and other styles

33

Andersson, Andreas. "State and Process Tomography : In Spekkens' Toy Model." Thesis, Linköpings universitet, Informationskodning, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-163156.

Full text

Abstract:

In 2004 Robert W. Spekkens introduced a toy theory designed to make a case for the epistemic view of quantum mechanics. But how does Spekkens’ toy model differ from quantum theory? While some differences are well-established, we attempt to approach this question from a tomographic point of view. More speciﬁcally, we provide experimentally viableprocedureswhichenablesustocompletelycharacterizethestatesandgatesthatare available in the toy model. We show that, in contrast to quantum theory, decompositions of transformations in the toy model must be done in a non-linear fashion.

APA, Harvard, Vancouver, ISO, and other styles

34

Eakins, Jonathan Simon. "Classical and quantum causality in quantum field theory, or, "the quantum universe"." Thesis, University of Nottingham, 2004. http://eprints.nottingham.ac.uk/10069/.

Full text

Abstract:

Based on a number of experimentally verified physical observations, it is argued that the standard principles of quantum mechanics should be applied to the Universe as a whole. Thus, a paradigm is proposed in which the entire Universe is represented by a pure state wavefunction contained in a factorisable Hilbert space of enormous dimension, and where this statevector is developed by successive applications of operators that correspond to unitary rotations and Hermitian tests. Moreover, because by definition the Universe contains everything, it is argued that these operators must be chosen self-referentially; the overall dynamics of the system is envisaged to be analogous to a gigantic, self-governing, quantum computation. The issue of how the Universe could choose these operators without requiring or referring to a fictitious external observer is addressed, and this in turn rephrases and removes the traditional Measurement Problem inherent in the Copenhagen interpretation of quantum mechanics. The processes by which conventional physics might be recovered from this fundamental, mathematical and global description of reality are particularly investigated. Specifically, it is demonstrated that by considering the changing properties, separabilities and factorisations of both the state and the operators as the Universe proceeds though a sequence of discrete computations, familiar notions such as classical distinguishability, particle physics, space, time, special relativity and endo-physical experiments can all begin to emerge from the proposed picture. A pregeometric vision of cosmology is therefore discussed, with all of physics ultimately arising from the relationships occurring between the elements of the underlying mathematical structure. The possible origins of observable physics, including physical objects positioned at definite locations in an arena of apparently continuous space and time, are consequently investigated for a Universe that incorporates quantum theory as a fundamental feature. Overall, a framework for quantum cosmology is introduced and explored which attempts to account for the existence of time, space, matter and, eventually, everything else in the Universe, from a physically consistent perspective.

APA, Harvard, Vancouver, ISO, and other styles

35

Orús, Lacort Román. "Entanglement, quantum phase transitions and quantum algorithms." Doctoral thesis, Universitat de Barcelona, 2006. http://hdl.handle.net/10803/482202.

Full text

Abstract:

From the seminal ideas of Feynman and until now, quantum information and computation has been a rapidly evolving field. While at the beginning, physicists looked at quantum mechanics as a theoretical framework to describe the fundamental processes that take place in Nature, it was during the 80’s and 90’s that people began to think about the intrinsic quantum behavior of our world as a tool to eventually develop powerful information technologies. As Landauer pointed out, information is physical, so it should not look strange to try to bring together quantum mechanics and information theory. Indeed, it was soon realized that it is possible to use the laws of quantum physics to perform tasks which are unconceivable within the framework of classical physics. For instance, the discovery of quantum teleportation, superdense coding, quantum cryptography, Shor’s factorization algorithm or Grover’s searching algorithm, are some of the remarkable achievements that have attracted the attention of many people, both scientists and non-scientists. This settles down quantum information as a genuine interdisciplinary field, bringing together researchers from different branches of physics, mathematics and engineering. While until recently it was mostly quantum information science that benefited from other fields, today the tools developed within its framework can be used to study problems of different areas, like quantum many-body physics or quantum field theory. The basic reason behind that is the fact that quantum information develops a detailed study of quantum correlations, or quantum entanglement. Any physical system described by the laws of quantum mechanics can then be considered from the perspective of quantum information by means of entanglement theory. It is the purpose of this introduction to give some elementary background about basic concepts of quantum information and computation, together with its possible relation to other fields of physics, like quantum many-body physics. We begin by considering the definition of a qubit, and move then towards the definition of entanglement and the convertibility properties of pure states by introducing majorization and the von Neumann entropy. Then, we consider the notions of quantum circuit and quantum adiabatic algorithm, and move towards what is typically understood by a quantum phase transition, briefly sketching how this relates to renormalization and conformal field theory. We also comment briefly on some possible experimental implementations of quantum computers
Desde las pioneras ideas de Feynman hasta el día de hoy, la información y computación cuánticas han evolucionado de forma veloz. Siendo la mecánica cuántica en sus orígenes considerada esencialmente como un marco teórico en el que poder explicar ciertos procesos fundamentales que acontecían en la Naturaleza, fue durante los años 80 y 90 cuando se empezó a pensar sobre el comportamiento intrínsecamente cuántico del mundo en el que vivimos como una herramienta con la que poder desarrollar tecnologías de la información más potentes, basadas en los mismos principios de la física cuántica. Tal y como Landauer dijo, la información es física, por lo que no debe en absoluto extrañarnos el que se intentara comulgar la mecánica cuántica con la teoría de la información. Y nada más lejos de la realidad, pues pronto se vio que era posible utilizar las leyes de la física cuántica para realizar tareas inconcebibles desde un punto de vista clásico. Por ejemplo, el descubrimiento de la teleportación, la codificación superdensa, la criptografía cuántica, el algoritmo de factorización de Shor o el algoritmo de búsqueda de Grover, constituyen algunos de los logros remarcables que han atraído la atención de mucha gente, dentro y fuera de la ciencia. Queda la información cuántica, pues, constituida como un campo genuinamente pluridisciplinar, en el que se concentran investigadores provenientes de diferentes ramas de la física, las matemáticas y la ingeniería. Mientras en sus orígenes era la información cuántica quien se beneficiaba del conocimiento de otros campos, a día de hoy las herramientas desarrolladas en el marco de la teoría cuántica de la información pueden ser asimismo usadas en el estudio de problemas de diferentes áreas, como la física de muchos cuerpos o la teoría cuántica de campos. Ello es debido al estudio detallado que la información cuántica desarrolla de las correlaciones cuánticas, o entrelazamiento cuántico. Cualquier sistema físico descrito por las leyes de la mecánica cuántica se puede por lo tanto considerar bajo la perspectiva de la teoría cuántica de la información a través de la teoría del entrelazamiento.

APA, Harvard, Vancouver, ISO, and other styles

36

Maring, Nicolas. "Quantum frecuency conversion for hybrid quantum networks." Doctoral thesis, Universitat Politècnica de Catalunya, 2018. http://hdl.handle.net/10803/663202.

Full text

Abstract:

The ability to control the optical frequency of quantum state carriers (i.e. photons) is an important functionality for future quantum networks. It allows all matter quantum systems - nodes of the network - to be compatible with the telecommunication C-band, therefore enabling long distance fiber quantum communication between them. It also allows dissimilar nodes to be connected with each other, thus resulting in heterogeneous networks that can take advantage of the different capabilities offered by the diversity of its constituents. Quantum memories are one of the building blocks of a quantum network, enabling the storage of quantum states of light and the entanglement distribution over long distances. In our group, two different types of memories are investigated: a cold atomic ensemble and an ion-doped crystal. In this thesis I investigate the quantum frequency conversion of narrow-band photons, emitted or absorbed by optical quantum memories, with two different objectives: the first one is to connect quantum memories emitting or absorbing visible single photons with the telecommunication wavelengths, where fiber transmission loss is minimum. The second and main goal is to study the compatibility between disparate quantum nodes, emitting or absorbing photons at different wavelengths. More precisely the objective is to achieve a quantum connection between the two optical memories studied using quantum frequency conversion techniques. The main core of this work is the quantum frequency conversion interface that bridges the gap between the cold ensemble of Rubidium atoms, emitting photons at 780nm, and the Praseodymium ion doped crystal, absorbing photons at 606nm. This interface is composed of two different frequency conversion devices, where a cascaded conversions takes place: the first one converts 780nm photons to the telecommunication C-band, and the second one converts them back to visible, at 606nm. This comes with several challenges such as conversion efficiency, phase stability and parasitic noise reduction, which are important considerations to show the conservation of quantum behaviors through the conversion process. This work can be divided in three parts. In a first one, we built a quantum frequency conversion interface between 606nm and the C-band wavelength, capable of both up and down-conversion of single photon level light. We also characterized the noise processes involved in this specific conversion. In the down-conversion case we showed that memory compatible heralded single photons emitted from a photon pair source preserve their non-classical properties through the conversion process. In the up-conversion case, we showed the storage of converted telecom photons in the praseodymium doped crystal, and their retrieval with high signal to noise ratio. The second part of the work was devoted to the conversion of photons from an emissive Rubidium atomic quantum memory to the telecom C band. In this work we converted the heralding photons from the atomic ensemble and measured non-classical correlations between a stored excitation and a C-band photon, necessary for quantum repeater applications. In the last part of the thesis, we setup the full frequency conversion interface and showed that heralded photons emitted by the atomic ensemble are converted, stored in the solid state memory and retrieved with high signal to noise ratio. We demonstrated that a single collective excitation stored in the atomic ensemble is transfered to the crystal by mean of a single photon at telecom wavelength. We also showed time-bin qubit transfer between the two quantum memories. This work represents the first proof of principle of a photonic quantum connection between disparate quantum memory nodes. The results presented in this thesis pave the way towards the realization of modular and hybrid quantum networks.

APA, Harvard, Vancouver, ISO, and other styles

37

Baghali, Khanian Zahra. "From Quantum Source Compression to Quantum Thermodynamics." Doctoral thesis, Universitat Autònoma de Barcelona, 2020. http://hdl.handle.net/10803/671034.

Full text

Abstract:

Aquesta tesi aborda problemes en el camp de la teoria de la informació quàntica, específicament, la teoria quàntica de Shannon. La primera part de la tesi comença amb definicions concretes de models de fonts quàntiques generals i la seva compressió, i cada capítol següent aborda la compressió d’un model de font específic com a casos especials dels models generals definits inicialment. Primer, trobem la taxa de compressió òptima d’una font d’estats barreja general que inclou com a casos especials tots els models prèviament estudiats, com les fonts pures i de col·lectivitats de Schumacher, i altres models de col·lectiuvitats d’estats barreja. Per a una interpolació entre els models de col·lectivitats visible i cec de Schumacher, trobem la regió de compressió òptima per les taxes d’entrellaçament i les taxes quàntiques. A continuació, estudiem exhaustivament la variació clàssic-quàntica del famós problema de Slepian-Wolf i trobem les taxes òptimes considerant la fidelitat per còpia; per la fidelitat de bloc trobem expressions tancades per les fites assolibles i inverses que coincideixen, sota la condició de que una funció que apareix a les dues fites sigui continua. La primera part de la tesi tanca amb un capítol sobre el model de col·lectivitats per la redistribució d’estats quàntics per al qual trobem la taxa de compressió òptima considerant la fidelitat per còpia i les fites assolibles i inverses, que de nou que coincideixen sota la condició de continuïtat d’una certa funció. La segona part de la tesis gira al voltant de la termódinamica quàntica sota de la perspectiva de la teoria de la informació. Comencem amb un punt de vista de la teoria de recursos d’un sistema quàntic amb múltiples càrregues que no commuten i amb objectes i operacions permeses que son termodinàmicament significatives; utilitzant eines de la teoria quàntica de Shannon classifiquem els objectes i trobem operacions quàntiques explícites que relacionen els objectes de la mateixa classe entre sí. Posteriorment, apliquem aquest marc de la teoria de recursos per estudiar una configuració termodinàmica tradicional amb múltiples quantitats conservades que no commuten que consta d’un sistema principal, un reservori calòric i bateries per emmagatzemar diverses quantitats conservades del sistema. Enunciem les lleis de la termodinàmica per a aquest sistema, i mostrem que un efecte purament quàntic té lloc en algunes transformacions del sistema, és a dir, algunes transformacions només són factibles si hi ha correlacions quàntiques entre l’estat final del sistema i del reservori calòric.
Esta tesis aborda problemas en el campo de la teoría de la información cuántica, específicamente, la teoría cuántica de Shannon. La primera parte de la tesis comienza con definiciones concretas de modelos de fuentes cuánticas generales y su compresión, y cada capítulo subsiguiente aborda la compresión de un modelo de fuente específico como casos especiales de los modelos generales definidos inicialmente. Primero, encontramos la tasa de compresión óptima de una fuente de estado mixto general que incluye como casos especiales todos los modelos previamente estudiados, como las fuentes pura y colectiva de Schumacher, y otros modelos colectivos de estado mixto. Para una interpolación entre el modelo colectivo visible y ciego de Schumacher, encontramos la región de tasa de compresión óptima para el entrelazamiento y las tasas cuánticas. A continuación, estudiamos exhaustivamente la variación clásico-cuántica del célebre problema de Slepian-Wolf y encontramos las tasas óptimas considerando la fidelidad por copia; con la fidelidad de bloque encontramos límites alcanzables e inversos que coinciden con la continuidad de una función que aparece en los límites. La primera parte de la tesis cierra con un capítulo sobre el modelo colectivo de redistribución de estado cuántico para el cual encontramos la tasa de compresión óptima considerando la fidelidad por copia y los límites alcanzables e inversos que coinciden con la continuidad de una función que aparece en los límites. La segunda parte de la tesis gira en torno a la perspectiva teórica de la información de la termodinámica cuántica. Comenzamos con un punto de vista de la teoría de recursos de un sistema cuántico con múltiples cargas no conmutables con objetos y operaciones permitidas que son termodinámicamente significativas; usando herramientas de la teoría cuántica de Shannon clasificamos los objetos y encontramos operaciones cuánticas explícitas que mapean los objetos de la misma clase entre sí. Posteriormente, aplicamos este marco de la teoría de recursos para estudiar una configuración termodinámica tradicional con múltiples cantidades no conmutables compuesta por un sistema principal, un reservorio calórico y baterías para almacenar varias cantidades conservadas del sistema. Enunciamos las leyes de la termodinámica para este sistema, y mostramos que ocurre un efecto puramente cuántico en algunas transformaciones del sistema, es decir, algunas transformaciones solo son factibles si existen correlaciones cuánticas entre el estado final del sistema y del reservorio calórico.
This thesis addresses problems in the field of quantum information theory, specifically, quantum Shannon theory. The first part of the thesis is opened with concrete definitions of general quantum source models and their compression, and each subsequent chapter addresses the compression of a specific source model as a special case of the initially defined general models. First, we find the optimal compression rate of a general mixed state source which includes as special cases all the previously studied models such as Schumacher’s pure and ensemble sources and other mixed state ensemble models. For an interpolation between the visible and blind Schumacher’s ensemble model, we find the optimal compression rate region for the entanglement and quantum rates. Later, we comprehensively study the classical-quantum variation of the celebrated Slepian-Wolf problem and find the optimal rates considering per-copy fidelity; with block fidelity we find single letter achievable and converse bounds which match up to continuity of a function appearing in the bounds. The first part of the thesis is closed with a chapter on the ensemble model of quantum state redistribution for which we find the optimal compression rate considering per-copy fidelity and single-letter achievable and converse bounds matching up to continuity of a function which appears in the bounds. The second part of the thesis revolves around information theoretical perspective of quantum thermodynamics. We start with a resource theory point of view of a quantum system with multiple non-commuting charges where the objects and allowed operations are thermodynamically meaningful; using tools from quantum Shannon theory we classify the objects and find explicit quantum operations which map the objects of the same class to one another. Subsequently, we apply this resource theory framework to study a traditional thermodynamics setup with multiple non-commuting conserved quantities consisting of a main system, a thermal bath and batteries to store various conserved quantities of the system. We state the laws of the thermodynamics for this system, and show that a purely quantum effect happens in some transformations of the system, that is, some transformations are feasible only if there are quantum correlations between the final state of the system and the thermal bath.

APA, Harvard, Vancouver, ISO, and other styles

38

Hausser, Frank. "Lattice quantum field theories with quantum symmetry." [S.l. : s.n.], 1998. http://darwin.inf.fu-berlin.de/1998/10/index.html.

Full text

APA, Harvard, Vancouver, ISO, and other styles

39

Mostame, Sarah. "On Quantum Simulators and Adiabatic Quantum Algorithms." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1231423737511-80057.

Full text

Abstract:

This Thesis focuses on different aspects of quantum computation theory: adiabatic quantum algorithms, decoherence during the adiabatic evolution and quantum simulators. After an overview on the area of quantum computation and setting up the formal ground for the rest of the Thesis we derive a general error estimate for adiabatic quantum computing. We demonstrate that the first-order correction, which has frequently been used as a condition for adiabatic quantum computation, does not yield a good estimate for the computational error. Therefore, a more general criterion is proposed, which includes higher-order corrections and shows that the computational error can be made exponentially small – which facilitates significantly shorter evolution times than the first-order estimate in certain situations. Based on this criterion and rather general arguments and assumptions, it can be demonstrated that a run-time of order of the inverse minimum energy gap is sufficient and necessary. Furthermore, exploiting the similarity between adiabatic quantum algorithms and quantum phase transitions, we study the impact of decoherence on the sweep through a second-order quantum phase transition for the prototypical example of the Ising chain in a transverse field and compare it to the adiabatic version of Grover’s search algorithm. It turns out that (in contrast to first-order transitions) the impact of decoherence caused by a weak coupling to a rather general environment increases with system size (i.e., number of spins/qubits), which might limit the scalability of the system. Finally, we propose the use of electron systems to construct laboratory systems based on present-day technology which reproduce and thereby simulate the quantum dynamics of the Ising model and the O(3) nonlinear sigma model.

APA, Harvard, Vancouver, ISO, and other styles

40

Dumlu, Cesim Kadri. "Quantum Decoherence And Quantum State Diffusion Formalism." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608563/index.pdf.

Full text

Abstract:

Foundational problems of quantum theory, regarding the appearance of classicality and the measurement problem are stated and their link to studies of open quantum systems is discussed. This study'
s main aim is to analyze the main approaches that are employed in the context of open quantum systems. The general form of Markovian master equations are derived by a constructive approach. The Quantum State Diffusion (QSD) formalism is stressed upon as an alternative method to the master equations. Using the Caldeira-Leggett model in the context of QSD, stationary solutions of a charged particle exposed to a uniform magnetic field are found. The important points are summarized and the results are discussed.

APA, Harvard, Vancouver, ISO, and other styles

41

Jacobs, Kurt Aaron. "Topics in quantum measurement and quantum noise." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300587.

Full text

APA, Harvard, Vancouver, ISO, and other styles

42

Gupta, Neha. "Homotopy quantum field theory and quantum groups." Thesis, University of Warwick, 2011. http://wrap.warwick.ac.uk/38110/.

Full text

Abstract:

The thesis is divided into two parts one for dimension 2 and the other for dimension 3. Part one (Chapter 3) of the thesis generalises the definition of an n-dimensional HQFT in terms of a monoidal functor from a rigid symmetric monoidal category X-Cobn to any monoidal category A. In particular, 2-dimensional HQFTs with target K(G,1) taking values in A are generated from any Turaev G-crossed system in A and vice versa. This is the generalisation of the theory given by Turaev into a purely categorical set-up. Part two (Chapter 4) of the thesis generalises the concept of a group-coalgebra, Hopf group-coalgebra, crossed Hopf group-coalgebra and quasitriangular Hopf group-coalgebra in the case of a group scheme. Quantum double of a crossed Hopf group-scheme coalgebra is constructed in the affine case and conjectured for the more general non-affine case. We can construct 3-dimensional HQFTs from modular crossed G-categories. The category of representations of a quantum double of a crossed Hopf group-coalgebra is a ribbon (quasitriangular) crossed group-category, and hence can generate 3-dimensional HQFTs under certain conditions if the category becomes modular. However, the problem of systematic finding of modular crossed G-categories is largely open.

APA, Harvard, Vancouver, ISO, and other styles

43

Venegas-Andraca, Salvador Elías. "Discrete quantum walks and quantum image processing." Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427612.

Full text

Abstract:

In this thesis we have focused on two topics: Discrete Quantum Walks and Quantum Image Processing. Our work is a contribution within the field of quantum computation from the perspective of a computer scientist. With the purpose of finding new techniques to develop quantum algorithms, there has been an increasing interest in studying Quantum Walks, the quantum counterparts of classical random walks. Our work in quantum walks begins with a critical and comprehensive assessment of those elements of classical random walks and discrete quantum walks on undirected graphs relevant to algorithm development. We propose a model of discrete quantum walks on an infinite line using pairs of quantum coins under different degrees of entanglement, as well as quantum walkers in different initial state configurations, including superpositions of corresponding basis states. We have found that the probability distributions of such quantum walks have particular forms which are different from the probability distributions of classical random walks. Also, our numerical results show that the symmetry properties of quantum walks with entangled coins have a non-trivial relationship with corresponding initial states and evolution operators. In addition, we have studied the properties of the entanglement generated between walkers, in a family of discrete Hadamard quantum walks on an infinite line with one coin and two walkers. We have found that there is indeed a relation between the amount of entanglement available in each step of the quantum walk and the symmetry of the initial coin state. However, as we show with our numerical simulations, such a relation is not straightforward and, in fact, it can be counterintuitive. Quantum Image Processing is a blend of two fields: quantum computation and image processing. Our aim has been to promote cross-fertilisation and to explore how ideas from quantum computation could be used to develop image processing algorithms. Firstly, we propose methods for storing and retrieving images using non-entangled and entangled qubits. Secondly, we study a case in which 4 different values are randomly stored in a single qubit, and show that quantum mechanical properties can, in certain cases, allow better reproduction of original stored values compared with classical methods. Finally, we briefly note that entanglement may be used as a computational resource to perform hardware-based pattern recognition of geometrical shapes that would otherwise require classical hardware and software.

APA, Harvard, Vancouver, ISO, and other styles

44

Poletti, Stephen John. "Geometry, quantum field theory and quantum cosmology." Thesis, University of Newcastle Upon Tyne, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315921.

Full text

APA, Harvard, Vancouver, ISO, and other styles

45

Nutz, Thomas. "Semiconductor quantum light sources for quantum computing." Thesis, Imperial College London, 2018. http://hdl.handle.net/10044/1/63931.

Full text

Abstract:

Semiconductor quantum dots can be used as sources of entangled single photons, which constitute a crucial resource for optical quantum computing. We present theoretical research on entanglement verification and nuclear spin physics, leading to results that are relevant to both experimental work and the theory of quantum optics and mesoscopic quantum systems. Optical quantum computing requires large entangled photonic states, yet characterizing even few-photon states is a challenge in current experiments due to low photon detection efficiencies. We present a lower bound on a measure of computational usefulness of a potentially large quantum state that requires only measured values of three-photon correlations. Hence this bound provides a simple and applicable benchmarking method for quantum dot experiments. We then turn to the critical issue of the interaction between electron and nuclear spins in quantum dots. This interaction gives rise to decoherence that stands in the way of generating entangled photons as well as nuclear phenomena that might help to overcome this challenge. We formulate a quantum mechanical model of the nuclear spin system in a quantum dot driven by continuous-wave laser light. Based on the analytical steady state solution of this model we predict a novel nuclear spin effect, giving rise to nuclear spin polarization that counteracts the effect of an external magnetic field. Beyond the decoherence problem nuclear spins give rise to randomly time-varying transition energies. A quantum mechanical model of this noise as well as the effect of photon scattering is developed, leading to the insight that optical driving can continuously probe the electron transition energy and thereby prevent it from changing.

APA, Harvard, Vancouver, ISO, and other styles

46

Weinstein, Yaakov Shmuel 1974. "The quantum Fourier transform and quantum chaos." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/17023.

Full text

Abstract:

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2003.
Includes bibliographical references (p. 127-133).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
In this thesis I study control of quantum systems while implementing complex quantum operations. Through experimental implementations of such operations, I test the accuracy of control and provide methods for identifying the type and strength of experimental errors. The centerpiece of this work is the quantum Fourier transform (QFT), an essential gate for quantum algorithms and quantum simulations. Experiments are performed on a three qubit liquid-state nuclear magnetic resonance quantum information processor, and demonstrate salient features of the QFT in both of these venues. The first experiment exhibits the ability of the QFT to extract periodicity, a necessary process for many quantum algorithms. As an example of a quantum simulation, I implement a three qubit quantum baker's map, which is composed of QFTs, and discuss how various conjectures of quantum chaos could be experimentally realized on a quantum computer. Another example of complex quantum operations are 'pseudo-random' maps. These are operators which pass statistical tests of randomness but can be efficiently implemented on a quantum computer. I explore the importance of pseudo-random maps for the study of quantum chaos and a host of quantum information processing protocols. I also implement a set of such maps experimentally. In order to determine the type and strength of the errors effecting our implemetations, quantum process tomography is done on the QFT.
(cont.) From the constructed QFT superoperator and Kraus forms I show how best to analyze the data in order to extract information about coherent, incoherent, and decoherent errors. Finally, I explore fidelity decay as a signature of quantum chaos. The simulations performed concentrate on the exact determination of fidelity decay behavior for quantum chaotic systems, and attempt to identify properties of the evolution operator that cause the observed fidelity decay behavior.
by Yaakov Shmuel Weinstein.
Ph.D.

APA, Harvard, Vancouver, ISO, and other styles

47

Altunata, Serhan. "Generalized quantum defect methods in quantum chemistry." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/36257.

Full text

Abstract:

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2006.
Vita.
Includes bibliographical references (p. 247-254).
The reaction matrix of multichannel quantum defect theory, K, gives a complete picture of the electronic structure and the electron - nuclear dynamics for a molecule. The reaction matrix can be used to examine both bound states and free electron scattering properties of molecular systems, which are characterized by a Rydberg/scattering electron incident on an ionic-core. An ab initio computation of the reaction matrix for fixed molecular geometries is a substantive but important theoretical effort. In this thesis, a generalized quantum defect method is presented for determining the reaction matrix in a form which minimizes its energy dependence. This reaction matrix method is applied to the Rydberg electronic structure of Calcium monofluoride. The spectroscopic quantum defects for the ... states of CaF are computed using an effective one-electron calculation. Good agreement with the experimental values is obtained. The E-symmetry eigenquantum defects obtained from the CaF reaction matrix are found to have an energy dependence characteristic of a resonance. The analysis shows that the main features of the energy-dependent structure in the eigenphases are a consequence of a broad shape resonance in the 2E+ Rydberg series.
(cont.) This short-lived resonance is spread over the entire 2E+ Rydberg series and extends well into the ionization continuum. The effect of the shape resonance is manifested as a global "scarring" of the Rydberg spectrum, which is distinct from the more familiar local level-perturbations. This effect has been unnoticed in previous analyses. The quantum chemical foundation of the quantum defect method is established by a many-electron generalization of the reaction matrix calculation. Test results that validate the many-electron theory are presented for the quantum defects of the lsagnpo, E+ Rydberg series of the hydrogen molecule. It is possible that the reaction matrix calculations on CaF and H2 can pave the way for a novel type of quantum chemistry that aims to calculate the electronic structure over the entire bound-state region, as opposed to the current methods that focus on state by state calculations.
by Serhan Altunata.
Ph.D.

APA, Harvard, Vancouver, ISO, and other styles

48

Chan, Ka Ho Adrian. "Quantum information processing with semiconductor quantum dots." Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648684.

Full text

APA, Harvard, Vancouver, ISO, and other styles

49

Xu, Xiulai. "InAs quantum dots for quantum information processing." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615012.

Full text

APA, Harvard, Vancouver, ISO, and other styles

50

Kerr, Steven. "Topological quantum field theory and quantum gravity." Thesis, University of Nottingham, 2014. http://eprints.nottingham.ac.uk/14094/.

Full text

Abstract:

This thesis is broadly split into two parts. In the first part, simple state sum models for minimally coupled fermion and scalar fields are constructed on a 1-manifold. The models are independent of the triangulation and give the same result as the continuum partition functions evaluated using zeta-function regularisation. Some implications for more physical models are discussed. In the second part, the gauge gravity action is written using a particularly simple matrix technique. The coupling to scalar, fermion and Yang-Mills fields is reviewed, with some small additions. A sum over histories quantisation of the gauge gravity theory in 2+1 dimensions is then carried out for a particular class of triangulations of the three-sphere. The preliminary stage of the Hamiltonian analysis for the (3+1)-dimensional gauge gravity theory is undertaken.

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Quantra'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles