To see the other types of publications on this topic, follow the link: Quantum confinement of light.
Dissertations / Theses on the topic 'Quantum confinement of light'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Quantum confinement of light.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Raciti, Rosario. "Quantum confinement effects on light absorption in Germanium for solar energy conversion." Doctoral thesis, Università di Catania, 2017. http://hdl.handle.net/10761/3689.
Full textAbstract:
The world demand for energy is continuously increasing with a rate that will soon become unsustainable given the current exploitation of energy sources (such as fossil fuels). In addition, it should be figured out that most of commonly used energy resource are limited and that humankind has liberated a quantity of carbon (as CO2) in the past 250 years that it took our planet about 250 million of years to sequester. In this context, a wide and exciting range of possible solutions to provide enough and cleaner energy is represented by nanotechnologies offering innovative materials with interesting effects exploitable for energy production, distribution and saving. Among other materials, Group-IV semiconductors have been deeply investigated since they allow the fabrication of abundant, non-toxic, mono-elemental nanostructures (as Si quantum dots, C nanotubes, Ge nanowires, et al.) thanks to high purity and mature technology. Moreover, fascinating effects due to quantum confinement in this nanostructures can be effectively exploited for energy production in photovoltaics devices. Among them, Ge reveals interesting optical properties due to its quasi-direct bandgap, higher absorption coefficient and larger exciton Bohr radius with respect to Si, giving the chance to easily tune the optical properties by exploiting quantum confinement effect (QCE). However, the properties of Ge quantum dots (QDs) depends not only on the size as many other parameters can concur in controlling their optical behavior, especially for what concerns the optical bandgap. For this reason, the aim of this thesis is devoted to a detailed investigation of the optical properties of Ge QD, with particular emphasis on the light absorption properties and its modulation by QCE.
2
Cosentino, Salvatore. "Germanium Nanostructures for Efficient Light Harvesting Devices." Doctoral thesis, Università di Catania, 2014. http://hdl.handle.net/10761/1524.
Full textAbstract:
The growing World energy demand is setting new challenges toward the use of alternative and green resources as well as for the development of more efficient and low-power consuming devices. Thanks to their unique optical properties, group IV (such as: Si, Ge, C) nanostructures (NS) show promising applications for cheap multi-junction solar cells and, in general, for efficient energy-tunable light harvesting devices. Among them, Ge reveals interesting optical properties due to its quasi-direct bandgap and larger absorption coefficient that make it intrinsically more suitable than Si for what concerns light harvesting applications. Moreover, the larger exciton Bohr radius of Ge (~24 nm) with respect to Si, gives the chance to easily tune the optical properties of Ge NSs by varying their size. However, the properties of Ge NS depends not only by size through quantum confinement effects, but many other parameters can concur in controlling their optical behavior, especially for what concerns the optical bandgap.
Discerning the role of these parameters and controlling their effects in the light absorption process contains not only a fundamental research theme, but represents a key-factor toward the implementation of Ge NS in any type of light harvesting device. For this reason, this thesis reports a detailed study on the synthesis, structural and optical properties of Ge nanostructures (quantum well, QW, or quantum dots, QDs) embedded in a dielectric matrix as well as the investigations of photo-conduction properties in prototypal light harvesting devices employing Ge NSs. Although the optical behavior of a single amorphous Ge QW can be fully modeled within the quantum confinement effect theory, this situation dramatically changes for a 3-dimensional confinement, as in an ensemble of QDs. In this last case, the effects of quantum confinement can be hidden or weakened by other parameters, such as: QD spacing and distribution, type and quality of the hosting matrix and abundance of defects related to the synthesis technique used. For this reason, we will investigate in detail the synthesis and optical properties of Ge QDs embedded in SiO2 or Si3N4 matrices, grown after thermal annealing of Ge-rich films synthesized by co-sputtering deposition; plasma enhanced chemical vapour deposition (PECVD) and ion implantation. We will give evidences of the strength of quantum confinement effects occurring in these systems as well as discerning the contributions coming from other concomitant effects. Finally, we will demonstrate that Ge nanostructures can be effectively used as active absorber and conductive medium in light harvesting devices. In particular, we will report on the spectral response of metal-insulating-semiconductor (MIS) photodetectors employing a single amorphous Ge QW or a packed array of Ge QDs as active light sensitizer and conductive medium. Both types of NSs have a fundamental role on the performances of these prototypal devices, demonstrating the large potentiality of such nanostructures for the development of high efficiency photodetectors and low cost solar cells.
3
Palacios-Berraquero, Carmen. "Quantum-confined excitons in 2-dimensional materials." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/275721.
Full textAbstract:
The 2-dimensional semiconductor family of materials called transition metal dichalcogenides (2d-TMDs) offers many technological advantages: low power consumption, atomically-precise interfaces, lack of nuclear spins and ease of functional integration with other 2d materials are just a few. In this work we harness the potential of these materials as a platform for quantum devices: develop a method by which we can deterministically create single-photon emitting sites in 2d-TMDs, in large-scale arrays. These we call quantum dots (QDs): quantum confinement potentials within semiconductor materials which can trap single-excitons. The single excitons recombine radiatively to emit single-photons. Single-photon sources are a crucial requirement for many quantum information technology (QIT) applications such as quantum cryptography and quantum communication. The QDs are formed by placing the flakes over substrates nano-patterned with protru- sions which induce local strain and provoke the quantum confinement of excitons at low temperatures. This method has been successfully tested in several TMD materials, hence achieving quantum light at different wavelengths. We present one of the very few systems where quantum confinement sites have been shown to be deterministically engineered in a scalable way. Moreover, we have demonstrated how the 2d-based QDs can be embedded within 2d- heterostructures to form functional quantum devices: we have used TMD monolayers along with other 2d-materials - graphene and hexagonal boron nitride - to create quan- tum light-emitting diodes that produce electrically-driven single-photons. Again, very few single-photon sources can be triggered electrically, and this provides a great ad- vantage when considering on-chip quantum technologies. Finally, we present experimental steps towards using our architecture as quantum bits: capturing single-spins inside the QDs, using field-effect type 2d-heterostructures. We are able to controllably charge the QDs with single-electrons and single-holes – a key breakthrough towards the use of spin and valley pseudospin of confined carriers in 2d-materials as a new kind of optically addressable matter qubit. This work presents the successful marriage of 2d-semiconductor technology with QIT, paving the way for 2-dimensional materials as platforms for scalable, on-chip quantum photonics.
4
Yoshioka, Hironori. "Fundamental Study on Si Nanowires for Advanced MOSFETs and Light-Emitting Devices." 京都大学 (Kyoto University), 2010. http://hdl.handle.net/2433/123341.
Full text
5
Toanen, Vincent. "Plasmons Tamm pour la réalisation de nouvelles sources de lumière." Electronic Thesis or Diss., Lyon 1, 2022. http://www.theses.fr/2022LYO10049.
Full textAbstract:
Les plasmons Tamm, ou modes Tamm optiques, sont des modes électromagnétiques présents à l'interface entre un miroir de Bragg (DBR) et une couche métallique. Ces modes présentent un fort intérêt pour la réalisation de nouvelles sources de lumière, notamment grâce à la partie métallique, qui peut d'une part fournir un contrôle et un confinement micrométrique à trois dimensions du mode optique, et d'autre part assurer l'injection d'un courant électrique dans la structure pour y exciter un milieu émetteur. De nombreuses sources de lumière pourraient être réalisées grâce à cette double fonction du métal, comme des sources polarisées intégrées, des générateurs de plasmons de surface ou encore des tableaux de laser adressables à grande échelle. Mon travail de doctorat a consisté à pousser les sources de lumière Tamm vers l'applicatif, en développant leur fonctionnement à température ambiante et en excitation électrique, par opposition aux démonstrations à température cryogénique et en pompage optique effectuées jusqu'alors. Ce développement a été effectué sur des structures semi-conductrices basées sur des alliages ternaires d'AlGaAs, mais est hautement transposable à d'autres familles de matériaux. La première partie de ce travail s'est concentrée sur l'obtention d'un effet laser à température ambiante. Grâce à une amélioration de la structure, consistant à insérer une couche de bas indice entre le DBR semi-conducteur et le métal, les pertes ohmiques dans ce dernier ont été réduites, ce qui a permis d'atteindre le régime laser à température ambiante. Le second volet de cette thèse concerne l'injection électrique des sources de lumière à mode Tamm. Partant d'un DBR dopé, deux procédés de micro-structuration en salle blanche ont été élaborés pour permettre cette injection. Le premier, inspiré de techniques usuelles de micro-fabrication, n'a pas fait ses preuves, en raison de la dégradation de la surface du DBR par certaines étapes classiques de structuration, et de la forte sensibilité du plasmon Tamm à la composition de surface du DBR. Nous avons donc développé une méthode de structuration alternative. Son originalité repose dans la protection permanente de la surface du DBR destinée au contact avec le métal. Cette nouvelle méthode a permis la fabrication des premières diodes électroluminescentes basées sur l'émission dans un mode Tamm. Leur caractérisation a montré la réussite de l'excitation du plasmon Tamm par l'injection électrique des émetteurs à puits quantiques, et prouve la possibilité d'utiliser un unique élément métallique pour confiner le mode optique et injecter les porteurs de charge. Ces résultats constituent une étape importante vers le développement d'une variété de sources de lumière intégrées utilisant les modes Tamm<br>Tamm plasmons, or optical Tamm states, are electromagnetic modes that exist at the interface between a Distributed Bragg Reflector (DBR) and a metallic layer. They are of high interest for the design of new light sources, thanks to the metallic part, which can provide 3D confinement and control of the optical mode but also electrical injection of the structure, in order to excite light emitters. Many light emitting devices could be realised using this dual function, such as integrated polarised light sources, surface plasmon generators or large-scale addressable laser arrays. This PhD work mainly consisted in pushing Tamm light emitting devices towards applicability, with the development of their room-temperature operation and electrical pumping, as opposed to previous demonstrations which were carried out under cryogenic temperature and optical pumping. Semiconducting heterostructures based on ternary alloys of AlGaAs were used for this development, but our results are highly transposable to other families of materials. The first part of this work focused on obtaining a laser effect at room temperature. By improving the structure with the insertion of a low-index layer between the semiconductor DBR and the metal, the ohmic losses in the metal were reduced, thus enabling lasing operation at room temperature. The second part of this work was about achieving the electrical injection of Tamm-based light sources. Starting from a doped DBR with quantum wells, we developed two processes, mostly based on cleanroom microfabrication techniques, to enable electrical injection. The first one, inspired by common microfabrication techniques, has not proved to be successful, due to the degradation of the DBR surface by some standard fabrication steps, and to the strong sensitivity of the Tamm plasmon to the surface composition of the DBR. Therefore, we developed a second method. Its originality lies in a permanent protection of the part of the DBR on which the metallic element will be deposited to form the Tamm mode and inject electrical current. This new method allowed the fabrication of the first light-emitting diodes based on Tamm mode emission. With electro-optical measurements, we demonstrated the excitation of the Tamm plasmon state through electrical pumping of the quantum wells, and proved the possibility to use a single metallic element to confine the optical mode and bring charge carriers into the structure. These results are an important step towards the development of new integrated light emitting devices using Tamm modes
6
Tsegaye, Takele Dessie. "Confinement Mechanisms in Quantum Chromodynamics." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1051373650.
Full text
7
Takele, Tsegaye. "Confinement mechanisms in quantum cherodynamics." Cincinnati, Ohio : University of Cincinnati, 2002. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=ucin1051373650.
Full text
8
Downing, Charles Andrew. "Quantum confinement in low-dimensional Dirac materials." Thesis, University of Exeter, 2015. http://hdl.handle.net/10871/17215.
Full textAbstract:
This thesis is devoted to quantum confinement effects in low-dimensional Dirac materials. We propose a variety of schemes in which massless Dirac fermions, which are notoriously diffcult to manipulate, can be trapped in a bound state. Primarily we appeal for the use of external electromagnetic fields. As a consequence of this endeavor, we find several interesting condensed matter analogues to effects from relativistic quantum mechanics, as well as entirely new effects and a possible novel state of matter. For example, in our study of the effective Coulomb interaction in one dimension, we demonstrate how atomic collapse may arise in carbon nanotubes or graphene nanoribbons, and describe the critical importance of the size of the band gap. Meanwhile, inspired by groundbreaking experiments investigating the effects of strain, we propose how to confine the elusive charge carriers in so-called velocity barriers, which arise due to a spatially inhomogeneous Fermi velocity triggered by a strained lattice. We also present a new and beautiful quasi-exactly solvable model of quantum mechanics, showing the possibilities for confinement in magnetic quantum dots are not as stringent as previously thought. We also reveal that Klein tunnelling is not as pernicious as widely believed, as we show bound states can arise from purely electrostatic means at the Dirac point energy. Finally, we show from an analytical solution to the quasi-relativistic two-body problem, how an exotic same-particle paring can occur and speculate on its implications if found in the laboratory.
9
Wesslén, Carl. "Confinement Sensitivity in Quantum Dot Spin Relaxation." Doctoral thesis, Stockholms universitet, Fysikum, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-142133.
Full textAbstract:
Quantum dots, also known as artificial atoms, are created by tightly confining electrons, and thereby quantizing their energies. They are important components in the emerging fields of nanotechnology where their potential uses vary from dyes to quantum computing qubits. Interesting properties to investigate are e.g. the existence of atom-like shell structures and lifetimes of prepared states. Stability and controllability are important properties in finding applications to quantum dots. The ability to prepare a state and change it in a controlled manner without it loosing coherence is very useful, and in some semiconductor quantum dots, lifetimes of up to several milliseconds have been realized. Here we focus on dots in semiconductor materials and investigate how the confined electrons are effected by their experienced potential. The shape of the dot will effect its properties, and is important when considering a suitable model. Structures elongated in one dimension, often called nanowires, or shaped as rings have more one-dimensional characteristics than completely round or square dots. The two-dimensional dots investigated here are usually modeled as harmonic oscillators, however we will also consider circular well models. The effective potential confining the electrons is investigated both in regard to how elliptical it is, as well as how results differ when using a harmonic oscillator or a circular well potential. By mixing spin states through spin-orbit interaction transitioning between singlet and triplet states becomes possible with spin independent processes such as phonon relaxation. We solve the spin-mixing two-electron problem numerically for some confinement, and calculate the phonon transition rate between the lowest energy singlet and triplet states using Fermi's golden rule. The strength of the spin-orbit interaction is varied both by changing the coupling constants, and by applying an external, tilted, magnetic field. The relation between magnetic field parameters and dot parameters are used to maximize state lifetimes, and to model experimental results.<br><p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.</p>
10
Abdelrahman, Ahmed M. "Magnetic micro-confinement of quantum degenerate gases." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2011. https://ro.ecu.edu.au/theses/411.
Full textAbstract:
In this dissertation we explore the basic principles of the magnetic micro-confinement of the quantum degenerate gases where the approach of the so-called two-dimensional magnetic lattices has been theoretically and experimentally investigated. In this research a new generation of two-dimensional magnetic lattice has been proposed and considered as a developing phase for the previous approaches. Its advantage relies on introducing a simplified method to create single or multiple micro-traps of magnetic field local minima distributed, at a certain working distance, above the surface of a thin film of permanent magnetic material. The simplicity in creating the magnetic field local minima at the micro-scale manifests itself as a result of imprinting specific patterns through the thin film using suitable and available micro-fabrication techniques. In this approach, to create multiple micro-traps, patterned square holes of size αh X αh spaced by αs are periodically distributed across the x/y plane taking a two-dimensional grid configuration. These magnetic field local minima are recognized by their ability to trap and confine quantum single-particles and quantum degenerate gases at various levels of distribution in their phase spaces, such as ultracold atoms and virtual quantum particles. Based on the nature of the interaction between the external confining potential fields and the different types of quantum particles, this research is conducted through two separate but not different phases. We performed theoretical and/or experimental investigations, for both phases, at the vicinity of the magnetic micro-confinement and its suitability for trapping quantum particles. A special attention is paid to inspect the coherence in such systems defined in terms of providing an accessible coupling to the internal quantum states of the magnetically trapped particles. Such coherence is considered as one of the important ingredients for simulating condensed matter systems and processing quantum information.
11
Harankahage, Dulanjan Padmajith Dharmasena. "Quantum Confinement Beyond the Exciton Bhor Radius in Quantum Dot Nanoshells." Bowling Green State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1593955468720583.
Full text
12
Tomczak, Nikodem. "Single light emitters in the confinement of polymers." Enschede : University of Twente [Host], 2005. http://doc.utwente.nl/57484.
Full text
13
Ring, Josh. "Novel fabrication and testing of light confinement devices." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/novel-fabrication-and-testing-of-light-confinement-devices(51572720-0c49-482e-8523-e44ca877117f).html.
Full textAbstract:
The goal of this project is to study novel nanoscale excitation volumes, sensitive enoughto study individual chromophores and go on to study new and exciting self assemblyapproaches to this problem. Small excitation volumes may be engineered using light con-finement inside apertures in metal films. These apertures enhance fluorescence emissionrates, quantum yields, decrease fluorescence quenching, enable higher signal-to-noiseratios and allow higher concentration single chromophore fluorescence, to be studied byrestricting this excitation volume. Excitation volumes are reported on using the chro-mophore's fluorescence by utilising fluorescence correlation spectroscopy, which monitorsfluctuations in fluorescence intensity. From the correlation in time, we can find the res-idence time, the number of chromophores, the volume in which they are diffusing andtherefore the fluorescence emission efficiency. Fluorescence properties are a probe ofthe local environment, a particularly powerful tool due to the high brightness (quantumyield) fluorescent dyes and sensitive photo-detection equipment both of which are readilyavailable, (such as avalanche photodiodes and photomultiplier tubes). Novel materialscombining the properties of conducting and non-conducting materials at scales muchsmaller than the incident wavelength are known as meta-materials. These allow combi-nations of properties not usually possible in natural materials at optical frequencies. Theproperties reported so far include; negative refraction, negative phase velocity, fluorescenceemission enhancement, lensing and therefore light confinement has also been proposed tobe possible. Instead of expensive and slow lithography methods many of these materialsmay be fabricated with self assembly techniques, which are truly nanoscopic and otherwiseinaccessible with even the most sophisticated equipment. It was found that nanoscaled volumes from ZMW and HMMs based on NW arrays wereall inefficient at enhancing fluorescence. The primary cause was the reduced fluorescencelifetime reducing the fluorescence efficiency, which runs contrary to some commentatorsin the literature. NW based lensing was found to possible in the blue region of the opticalspectrum in a HMM, without the background fluorescence normally associated with a PAAtemplate. This was achieved using a pseudo-ordered array of relatively large nanowireswith a period just smaller than lambda / 2 which minimised losses. Nanowires in the traditionalregime lambda / 10 produced significant scattering and lead to diffraction, such that they werewholly unsuitable for an optical lensing application.
14
Nutz, Thomas. "Semiconductor quantum light sources for quantum computing." Thesis, Imperial College London, 2018. http://hdl.handle.net/10044/1/63931.
Full textAbstract:
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.
15
李德豪 and Tak-ho Alex Li. "Stripe quantum well waveguides using implantation induced optical confinement." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1997. http://hub.hku.hk/bib/B31237381.
Full text
16
Koulentianos, Dimitrios. "Quantum confinement effect in materials for solar cell applications." Thesis, Uppsala universitet, Materialteori, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-237189.
Full text
17
Li, Tak-ho Alex. "Stripe quantum well waveguides using implantation induced optical confinement /." Hong Kong : University of Hong Kong, 1997. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19145421.
Full text
18
Sivarajah, Prasahnt. "THz polaritonics : control, confinement, and strong light-matter interactions." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/112443.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2017.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 195-206).<br>On the terahertz (THz) polaritonics platform, ultrafast optical laser pulses are used to generate and detect THz phonon-polariton wavepackets with full spatiotemporal resolution while they are confined to a thin slab of lithium niobate (LN) or lithium tantalate (LT) that is roughly 30-100 pm thick. Polaritonics is an attractive platform for wave-based computing because of its wealth of capabilities, but still requires the study and development of some critical features before applications can be fully realized. In my thesis work, I investigated and developed two of these features: photonic structures and strong light-matter coupling. In the first phase, we developed a fabrication procedure to pattern high-aspect ratio, optical-quality air holes into slabs of LN and LT, which has been historically difficult to achieve. We then studied the nature of THz wave propagation in the slabs when the size of these air holes was either much smaller or comparable to the THz wavelength. In the long-wavelength limit, where the structures are normally approximated as homogenous media, our findings were used to determine a cutoff-wavelength for operation and design of gradient refractive index devices. In the short wavelength limit, where the structures are termed photonic crystals, our work challenged the universally used definition of the Brillouin zone and presented an alternative definition that was valuable in understanding wave propagation in periodically ordered systems. In the second phase, we demonstrated a novel form of light-matter interaction in the strong coupling regime, where phonons and magnons where strongly coupled to the electric and magnetic fields of THz light, respectively. Our experiments, performed in both waveguide and cavity geometries, conclusively proved the formation of new quasiparticles we termed magnon-phonon-polaritons. We believe our results open up the possibility of using polaritonics for facile and coherent ultrafast control and conversion between photonic, phononic, and spin degrees of freedom, and thereby provides a promising avenue through which to explore THz wave-based computing. Our cavity geometry and sensitive detection scheme should also provide a means by which to pursue the field of THz cavity quantum electrodynamics.<br>by Prasahnt Sivarajah.<br>Ph. D.
19
Worrall, Anthony Duncan. "The Schwinger-Dyson equations and confinement in quantum chromo-dynamics." Thesis, Durham University, 1985. http://etheses.dur.ac.uk/7024/.
Full textAbstract:
The Schwinger-Dyson equations for the gluon and quark propagators are investigated in the covariant gauge. The renormalization functions are approximated suitably and the value of the parameters are determined by requiring that the functions be numerically self-consistent solutions over appropriate ranges of momenta. In the case of the gluon the Schwinger-Dyson equation is truncated by neglecting the the two loop contributions and the triple gluon vertex is approximated by a form proposed by Mandelstam which has the same behaviour as the more complicated longitudinal vertex determined from the Slavnov-Taylor identity. The equation is then closed and the integrals are calculated by dimensional regularization and renormalized to remove a mass term. In the quark case the dominant part of the quark-gluon vertex is determined from the Ward-Takahashi identity to give, with the gluon, a closed equation. The angular integrals are then calculated by an appropriate choice of coordinate frame. The quark function is approximated by a power series in the non-perturbative regime and the usual perturbative result elsewhere. The radial integrals are then calculated with appropriate regularization and renormalization. It is found that the gluon propagator has approximately a singularity of the form 1/q(^4) which leads to a roughly linear confining potential. The effect of this enhanced singularity on the quark propagator is to suppress the propagation of quarks at low momenta.
20
Weiss, Stephan. "Nonequilibrium quantum transport and confinement effects in interacting nanoscale conductors." Aachen Shaker, 2008. http://d-nb.info/990088294/04.
Full text
21
Hart, A. "Magnetic monopoles and confinement in lattice gauge theory." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337718.
Full text
22
Büttner, Kirsten. "Confinement and the infrared behaviour of the gluon propagator." Thesis, Durham University, 1996. http://etheses.dur.ac.uk/5298/.
Full textAbstract:
We investigate the infrared behaviour of the gluon propagator in Quantum Chromo- dynamics (QCD). A natural framework for such a non-perturbative study is the complex of Schwinger-Dyson equations (SDE).The possible infrared behaviour of the gluon, found by self-consistently solving the approximate boson SDE, is studied analytically. We find that only an infrared enhanced gluon propagator, as singular as 1/p(^4) as p(^2) → 0, is consistent and demonstrate why softer solutions, that others have found, are not allowed. Reassuringly the consistent, enhanced infrared behaviour is indicative of the confinement of quarks and gluons, implying, for example, area-law behaviour of the Wilson loop operator and forbidding a Kāllen-Lehmann spectral representation of both quark and gluon propagators. We then briefly consider the implications of these results for models of the pomeron. The enhancement of the gluon propagator does however introduce infrared divergences in the SDE and these need to be regularised. So far model forms of the enhanced gluon propagator have been used in studies of dynamical chiral symmetry breaking and hadron phenomenology. Though very encouraging results have been obtained, one might hope to use the gluon propagator obtained directly from non-perturbative QCD to calculate hadron observables. We therefore attempt to eliminate the infrared divergences in the SDEs in a self- consistent way, entirely within the context of the calculational scheme. To do this we introduce an infrared regulator λ in the truncated gluon SDE in quenched QCD. We find that this regulator is indeed determined by the equation and bounded by the QCD-scale Aqcd- Thus it is possible to perform the regularisation within the SDEs. However, we have not been able to choose λ < Aqcd.
23
Chille, Vanessa. "Quantum optics with structured light." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066358/document.
Full textAbstract:
La présente thèse a pour objectif d'analyser la lumière structurée non-classique et ses caractéristiques. L'optique quantique et la lumière structurée sont deux sujets qui font l'objet d'examens nombreux. Ils sont néanmoins rarement examinés en combinaison. Les propriétés quantiques de la lumière structurée sont moins bien étudiées qu'ils devraient l'être. Par la lumière structurée nous entendons les champs lumineux qui montrent une structure transverse complexe de l'intensité, la phase ou la polarisation. Nous voulons lier les deux sujets de l'optique quantique et la lumière structurée dans la présente thèse. Dans ce but, nous générons expérimentalement des champs lumineux structurés non-classiques. En particulier, nous réalisons une expérience qui permet de générer des faisceaux vectoriels vectoriels - c'est-à-dire des faisceaux lumineux dont l'état de polarisation présente une structure transverse complexe - qui montrent une réduction du bruit quantique. En outre, nous étudions théoriquement les propriétés spatiales de faisceaux lumineux, ainsi que leur bruit. Plus spécifiquement, nous analysons l'incertitude quantique dans la largeur d'un faisceau lumineux. Pour prouver la faisabilité de la vérification expérimentales de nos résultats théoriques, nous réalisons des simulations pour la mesure de paramètres spatiales utilisant un détecteur mulitpixels<br>This thesis aims at learning more about nonclassical structured light. Quantum optics and structured light are two topics that are subject to countless scientific examinations. However, they are very rarely combined and the quantum properties of structured light are not as thoroughly studied as they deserve. By structured light, we mean any light fields with complex transverse distributions of intensity, phase or polarization. We want to link the topics of quantum optics and structured light in this thesis. For this purpose, we experimentally generate particular nonclassical structured light fields. In particular, we construct an experimental setup that enables us, in principle, to produce arbitrary amplitude squeezed vector beams, i.e. light beams with a complex transverse structure of the state of polarization. Furthermore, we analyze spatial properties of light beams, and their quantum noise theoretically. We specifically perform theoretical examinations of the quantum noise in the width of a light beam. To show the feasibility of an experimental verification of our theoretical results, we conduct simulations for the measurement of spatial parameters of a beam's cross-section by a multipixel detector
24
Renken, Volker. "Electron confinement and quantum well states in two-dimensional magnetic systems." [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=985573546.
Full text
25
Sun, Xiangzhong 1968. "The effect of quantum confinement on the thermoelectric figure of merit." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9308.
Full textAbstract:
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1999.<br>Includes bibliographical references (p. 161-165).<br>The thermoelectric figure of merit (Z) determines the usefulness of a material for thermoelectric energy conversion applications. Since the 1960's, the best thermoelectric material has been Bi2Te3 alloys, with a ZT of 1.0 at a temperature ofT = 300 K. The advancement of nano-scale technologies has opened up the possibility of engineering materials at nano-scale dimensions to achieve low-dimensional thermoelectric structures which may be superior to their bulk forms. In this thesis, I established the basis of the low dimensional thermoelectric transport principle in the Si/Si1-xGex quantum well superlattice (two-dimensional) system and in the Bi quantum wire (one-dimensional) system. In bulk form, Si1_xGex is a promising thermoelectric material for high temperature applications. The Si/Si1 _xGex quantum well superlattice structures are studied based on their electronic band structures using semiclassical transport theory. Detailed subband structures are considered in an infinite series of finite height quantum wells and barriers. A significant enhancement of the thermoelectric figure of merit is expected. Based on my calculations, experimental studies are designed and performed on MBE grown Si/Sii -xGex quantum well superlattice structures. The experimental results are found to be consistent with theoretical predictions and indicate a significant enhancement of Z within the quantum wells over bulk values. The bismuth quantum wire system is a one-dimensional (ID) thermoelectric system. Bismuth as a semimetal is not a good thermoelectric material in bulk form becamm of the approximate cancellation between the electron and hole contributions to the Seebeck coefficient. However, quantum confinement can be introduced by making Bi nanowires to yield a ID semiconductor. ID transport properties are calculated along the principal crystallographic directions. By carefully tailoring the Bi wire size and carrier concentration, substantial enhancement in Z is expected. A preliminary experimental study of Bi nanowire arrays is also presented.<br>by Xiangzhong Sun.<br>Ph.D.
26
Andrew), Patterson Alex A. (Alex. "An analytical framework for field electron emission, incorporating quantum- confinement effects." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/84863.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 141-151).<br>As field electron emitters shrink to nanoscale dimensions, the effects of quantum confinement of the electron supply and electric field enhancement at the emitter tip play a significant role in determining the emitted current density (ECD). Consequently, the Fowler-Nordheim (FN) equation, which primarily applies to field emission from the planar surface of a bulk metal may not be valid for nanoscale emitters. While much effort has focused on studying emitter tip electrostatics, not much attention has been paid to the consequences of a quantum-confined electron supply. This work builds an analytical framework from which ECD equations for quantum-confined emitters of various geometries and materials can be generated and the effects of quantum confinement of the electron supply on the ECD can be studied. ECD equations were derived for metal emitters from the elementary model and for silicon emitters via a more physically-complete version of the elementary model. In the absence of field enhancement at the emitter tip, decreasing an emitter's dimensions is found to decrease the total ECD. When the effects of field enhancement are incorporated, the ECD increases with decreasing transverse emitter dimensions until a critical dimension dpeak, below which the reduced electron supply becomes the limiting factor for emission and the ECD decreases. Based on the forms of the ECD equations, alternate analytical methods to Fowler-Nordheim plots are introduced for parameter extraction from experimental field emission data. Analysis shows that the FN equation and standard analysis procedures over-predict the ECD from quantum-confined emitters. As a result, the ECD equations and methods introduced in this thesis are intended to replace the Fowler-Nordheim equation and related analysis procedures when treating field emission from suitably small field electron emitters.<br>by Alex A. Patterson.<br>S.M.
27
Riley, James R. "A Systematic Investigation of Quantum Confinement Effects in Bismuth Nanowire Arrays." Thesis, Boston College, 2009. http://hdl.handle.net/2345/693.
Full textAbstract:
Thesis advisor: Michael Graf<br>Bismuth is an interesting element to study because the low effective mass of its charge carriers makes the material sensitive to quantum confinement effects. When bismuth is reduced to the nanoscale two interesting phenomena may occur: it may transition from a semimetal to a semiconductor, or charge carriers in special surface states may begin to dominate the behavior of the material. Arrays of bismuth nanowires of various diameters were studied to investigate these possibilities. The magnetoresistance of the arrays was measured and the period of Shubnikov-de Haas oscillations suggested an increase in the effective mass and density of the material’s charge carriers for small nanowire diameters. These increases suggested that electrons were present in surface states and strongly influenced the material’s behavior when its dimensions were sufficiently reduced. The magnetization of the nanowire arrays was also measured and the lack of de Haas-van Alphen oscillations for certain diameter nanowires suggested that electrons were not present in surface states and that instead the material was transitioning from a semimetal to a semiconductor. Heat capacity measurements were planned to reconcile the two experiments. My detailed calculations demonstrated that heat capacity measurements were feasible to determine the presence, or absence, of surface charge carriers. Because the electronic contribution to the material’s heat capacity is small a calorimeter platform was constructed with ultra-low heat capacity components<br>Thesis (BS) — Boston College, 2009<br>Submitted to: Boston College. College of Arts and Sciences<br>Discipline: College Honors Program<br>Discipline: Physics
28
Amin, Victor. "Ligand-Mediated Control of the Confinement Potential in Semiconductor Quantum Dots." Thesis, Northwestern University, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3741337.
Full textAbstract:
<p> This thesis describes the mechanisms by which organic surfactants, particularly thiophenols and phenyldithiocarbamates, reduce the confinement potential experienced by the exciton of semiconductor quantum dots (QDs). The reduction of the confinement potential is enabled by the creation of interfacial electronic states near the band edge of the QD upon ligand adsorption. In the case of thiophenols, we find that this ligand adsorbs in two distinct binding modes, (i) a tightly bound mode capable of exciton delocalization, and (ii) a more weakly bound mode that has no discernable effect on exciton confinement. Both the adsorption constant and reduction in confinement potential are tunable by para substitution and are generally anticorrelated. For tightly bound thiophenols and other moderately delocalizing ligands, the degree of delocalization induced in the QD is approximately linearly proportional to the fractional surface area occupied by the ligand for all sizes of QDs. In the case of phenyldithiocarbamates, the reduction in the confinement potential is much greater, and ligand adjacency must be accounted for to model exciton delocalization. We find that at high surface coverages, exciton delocalization by phenyldithiocarbamates and other highly delocalizing ligands is dominated by ligand packing effects. Finally, we construct a database of electronic structure calculations on organic molecules and propose an algorithm that combines experimental and computational screening to find novel delocalizing ligands.</p>
29
Lan, Shau-Yu. "Matter-light entanglement with cold." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/28197.
Full textAbstract:
Thesis (M. S.)--Physics, Georgia Institute of Technology, 2009.<br>Committee Chair: Kuzmich, Alex; Committee Member: Chapman, Michael; Committee Member: Citrin, David; Committee Member: Kennedy, T. A. Brian; Committee Member: Raman, Chandra
30
Smith, Arlynn W. "Light confinement and hydrodynamic modeling of semiconductor structures by volumetric methods." Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/13407.
Full text
31
Foresi, James S. (James Serge). "Optical confinement and light guiding in high dielectric contrast materials systems." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10381.
Full text
32
Kim, Oleg. "Collectively enhanced quantum light-matter interactions." Thesis, University of Leeds, 2015. http://etheses.whiterose.ac.uk/10003/.
Full textAbstract:
In this thesis, we investigate dynamics of many-body atomic systems coupled to electromagnetic fields. We find that collective effects present in cavity-mediated laser cooling and high temperatures of bubble in sonoluminescence can be explained using a two-stage model which combines quantum-optical models and thermodynamical processes. We show how the collective processes are strongly dependent on mutual atomic coherences and how these coherences need to be recreated for the continous collective processes to take place. The model mechanism behind both cavity-mediated laser cooling and sonoluminescence heating is alternating periods of thermalisation with cooling or heating cycles. The thermalisation stage is characterised by relatively weak interactions between the atomic system and its environment, while allowing the system to thermalise and to create phonon and electronic coherences necessary for the next stage. The second stage, when cooling or heating occurs, marks strong interactions of the atomic system with the surrounding radiation field, which renders interactions between the particles negligible. During this stage, the atomic coherences created earlier fuel the cooling or heating process, allowing the system to reach a more beneficial stationary state. For cavity-mediated laser cooling of an atomic gas, we show that dispersing cooling pulses with periods of thermalisation in an asymmetric potential can result in very low temperatures of the atomic gas. By applying this to atomic interactions of sonoluminescence, we can describe different parts of the lifecycle of the cavitating bubble and how very high temperatures arise inside of it.
33
Patel, Sailesh. "Magneto-optical studies of 2D, 1D and 0D electron systems." Thesis, University of Exeter, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337804.
Full text
34
Alcalá, Gemma. "The positive light." Thesis, KTH, Arkitektur, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-280031.
Full textAbstract:
This Masters Thesis is a response to the personal willingness of obtaining something positive from the global crisis, caused by Covid-19. In such a situation, an understanding of the role of light in domiciles is appropriate not only functionally, but emotionally, as new ways of living in space are introduced. Indeed, flexibility has turned to be a claimed characteristic in the house, as well as access to daylight and outdoor spaces. Those aspects are to be considered positive in the near future. Nevertheless, what can be considered as positive light and the extent to which it is related to flexibility is a factor to study. How positive light can be achieved is also a factor to consider. Throughout this project, positive light will be defined under the exceptional circumstances of quarantine. The distribution of a survey, a discussion of architectural theories, as well as a study of positive light in my personal home will be carried out in order to gain an insight into its definition.
35
Ford, Frank R. "Loop study of Gribov-Zwanzigar confinement and mass operators in quantum chromodynamics." Thesis, University of Liverpool, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526882.
Full text
36
Weiss, Stephan [Verfasser]. "Nonequilibrium quantum transport and confinement effects in interacting nanoscale conductors / Stephan Weiss." Aachen : Shaker, 2008. http://d-nb.info/1162793899/34.
Full text
37
Eddie, Iain Mackenzie. "Carrier confinement in vertical-cavity surface-emitting lasers by quantum well intermixing." Thesis, University of Glasgow, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.433190.
Full text
38
Dorier, Vincent. "Quantum theory of light in linear media : applications to quantum optics and quantum plasmonics." Thesis, Bourgogne Franche-Comté, 2020. http://www.theses.fr/2020UBFCK006.
Full textAbstract:
Nous développons une méthode de quantification du champ électromagnétique en interaction linéaire avec les milieux passifs d'une part, et les milieux actifs (plasmoniques) d'autre part. Cette méthode repose sur la construction d'une structure Hamiltonienne compatible avec les équations de Maxwell, puis sur un principe de correspondence et la définition d'un espace de Fock des états quantiques. Nous utilisons les résultats de la théorie quantique pour étudier la propagation de photons dans des environnements diéléctriques et l'émission de plasmons uniques<br>We develop a method of quantization of the electromagnetic field interacting with passive media on one hand, and active (plasmonic) media on the other hand. This method relies on the construction of a Hamiltonian structure compatible with the Maxwell equations, and then on a principle of correspondence and the definition of a Fock space of quantum states. We use the results of the quantum theory to study the propagation of photons in dielectric environments and the emission of single plasmons
39
Yu, Hongwei. "Quantum lightcone fluctuations /." Thesis, Connect to Dissertations & Theses @ Tufts University, 2000.
Find full textAbstract:
Thesis (Ph.D.)--Tufts University, 2000.<br>Adviser: Lawrence H. Ford. Submitted to the Dept. of Physics and Astronomy. Includes bibliographical references (leaves 99-105). Access restricted to members of the Tufts University community. Also available via the World Wide Web;
40
Sidiropoulos, Themistoklis. "Enhanced light-matter interactions in laser systems incorporating metal-based optical confinement." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/30831.
Full textAbstract:
The aim of plasmonics is to exploit the strong coupling between photons and collective electron oscillations in metals, so-called surface plasmon polaritons, which enable a strong confinement of the electromagnetic field to metal-dielectric interfaces. The interaction of confined optical states with electronic transitions within matter accelerates these otherwise slow light-matter interactions. This work's purpose is to investigate accelerated light-matter interactions within plasmonic lasers, which arise due to optical confinement, and how these influence laser dynamics. In particular, this work focuses on the fabrication, demonstration and characterisation of plasmonic lasers. The devices investigated in this work consist of semiconductor nanowires made from zinc oxide (ZnO) placed in the proximity of a silver substrate. In this geometry the metal allows for strong optical confinement, whereas the semiconductor delivers the necessary gain to achieve lasing. Operating at room temperature, the emission from ZnO lies near the surface plasmon frequency, where confinement and loss become maximal, leading to accelerated spontaneous recombination, gain switching and gain recovery compared with conventional - photonic - ZnO nanowire lasers. To assess the lasing dynamics, in this work a novel double-pump spectroscopy technique is used, which exploits the non-linearity of the laser process to allow the investigation of accelerated light-matter interactions. This novel technique is necessary, as the speed of plasmonic devices is too fast for electrical detection, and the emission of single devices is too weak for non-linear spectroscopic techniques. Comparing photonic and plasmonic devices reveals contrasting dynamics between both, highlighting the benefits of plasmonic confinement, but also exposing an important limitation. Plasmonic devices could potentially be faster, but are ultimately limited by internal relaxation processes of the chosen gain medium. The findings of this work will improve the understanding of plasmonic lasers and their limitations, but also lead to improved knowledge of internal semiconductor processes.
41
Bouchard, Frédéric. "Classical and Quantum Dynamics of Twisted Light." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35209.
Full textAbstract:
This thesis encompasses a body of experimental work on the dynamics of twisted light. We first deal with the generation and reconstruction of twisted light for applications in classical and quantum physics, respectively. In the first case, we present a novel device that has the ability to generate twisted light in a manner that is completely wavelength-independent. Such a device may find applications in various fields of classical physics, ranging from nano to astronomical imaging. In the second work, we study the dynamics of twisted light in the case of laser-induced radial birefringence. This is done by studying the optical features resulting from elastic properties of silver-doped glass. In the last work on generation of twisted light, we present a nano-scale twisted light generator having the capacity to generate an optical mode with a controllable number of twists. In the context of quantum communication and quantum computations, this device has a great potential due to its small size and integrability. In the second part of the thesis, we study the propagation of twisted light both at the classical and quantum regime. In the first case, we observe exotic group velocities of light pulses in vacuum due to the twisting of its wavefront. In the second case, we study the effect of quantum decoherence of twisted light due to the coupling of photonic internal degrees of freedom. We present a technique to recover the lost coherence, which we name recoherence, by a practical unitary transformation.
42
Jeong, H. "Quantum information processing with non-classical light." Thesis, Queen's University Belfast, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398097.
Full text
43
Cao, Yameng. "Semiconductor light sources for photonic quantum computing." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/56619.
Full textAbstract:
The isolation of qubits from decoherence is crucial to the prospect of building revolutionary quantum devices. This work is devoted to an optical study of the decoherence on spin qubits in self-assembled quantum dots. This thesis contributes towards a complete understanding of quantum decoherence, of which highlighted discoveries include bypassing the spectral diffusion in neutral quantum dot emission lines; observing for the first time the self-polarization phenomenon of nuclear spins, via the resonance-locking effect on a negatively charged quantum dot; and revealing the limiting factors on hole spin dephasing, by measuring polarization correlations on a positively charged quantum dot. Three studies were conducted using two different spectroscopy techniques. For the first study, the spectral diffusion of emission line due to random electrostatic fluctuations was revealed, by scanning a neutral quantum dot transition across the laser resonance. Exciting the quantum dot resonantly bypassed this problem, paving the way for an on-demand antibunched source that generates narrow-band photons. For the second study, evidences supporting the spontaneous self-polarization of nuclear spins were observed for the first time, since it was predicted nearly four decades ago by M. Dyankonov and V.I. Perel. The self-polarization phenomenon is a remarkable demonstration of dynamic nuclear spin polarization since it manifests without the ground state electron being spin-polarized. In the last study, factors limiting the hole spin lifetime was inferred from measuring polarization correlation of successively emitted photons from a positively charged quantum dot. Evidences support a strong dependence on the carrier repopulation rate and the single electron spin dephasing in the upper state, due to the Overhauser field. In combination with the observation of spontaneous nuclear polarization, this opens the possibility of an electron spin sensor, which can indirectly probe the nuclear field.
44
Lyubomirsky, Ilya. "Quantum reality and squeezed states of light." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/36431.
Full textAbstract:
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1994.<br>Includes bibliographical references (leaves 67-71).<br>by Ilya Lyubomirsky.<br>M.S.
45
Konthasinghe, Kumarasiri. "Resonant Light Scattering from Semiconductor Quantum Dots." Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6527.
Full textAbstract:
In this work, resonant laser spectroscopy has been utilized in two major projects --resonance fluorescence measurements in solid-state quantum-confined nanostructures and laser-induced fluorescence measurements in gases. The first project focuses on studying resonant light-matter interactions in semiconductor quantum dots "artificial atoms" with potential applications in quantum information science. Of primary interest is the understanding of fundamental processes and how they are affected by the solid-state matrix. Unlike atoms, quantum dots are susceptible to a variety of environmental influences such as phonon scattering and spectral diffusion. These interactions alter the desired properties of the scattered light and hinder uses in certain single photon source applications. One application of current interest is the use of quantum dots in “quantum repeaters” for which two-photon interference is key. Motivated by such an application we have explored the limits imposed by environmental effects on two quantum dots in the same sample, the scattered light from which is being interfered. We find that both one-photon and two-photon interference, although substantial, are affected in a variety of ways, in particular by spectral diffusion. These observations are discussed and compared with a theoretical model. We further investigated correlations in pulsed resonance fluorescence, and found significant unexpected spectral and temporal deviations from those studied under continuous wave excitation. Under these conditions, the scattered light exhibits Rabi oscillations and photon anti-bunching, while maintaining a rich spectrum containing many spectral features. These observations are discussed and compared with a theoretical model. In the second project, the focus is on the investigation of the possibility of detecting N2+ ions in air using laser induced fluorescence, with potential applications in detection of fissile materials at a distance. A photon-counting analysis reveals that the fluorescence decay rate rapidly increases with increasing N2 pressure and thus limits the detection at elevated pressures, in particular at atmospheric pressure. We show that time-gated detection can be used to isolate N2+ fluorescence from delayed N2 emission. Based on the spontaneous Raman signal from N2 simultaneously observed with N2+ fluorescence, we could estimate a limit of detection in air of order 108-1010 cm3.
46
Nute, Jonathan. "A quantum integrated light and matter interface." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/41595/.
Full textAbstract:
A highly integrated device capable of interfacing light and matter on a chip is presented. 1e7 caesium-133 atoms are captured from a hot vapour into a magneto-optical trap held close to a chip-mounted single-mode fibre. Sub-Doppler optical molasses cools the atoms and transfers them into a tightly focused 18W vertical optical dipole trap which intersects a 30um void that has been laser etched through the single-mode fibre. Thus, the optically trapped atoms are tightly confined in the path of fibre-guided photons for maximum overlap. Such a system is capable of writing, reading and storing quantum information and clearly has massive implications for quantum information technologies. The device presented is adaptable, scalable and highly integrated making it the ideal building block for quantum computing. Developments and modifications made to a system for producing ultracold samples of lithium-6, caesium-133 and mixtures thereof is also presented. Feshbach molecules have major applications in quantum computing, particularly in the modelling of complex many-body quantum systems. The large dipolar moment of the lithium-caesium Feshbach molecule is the largest of all the alkali dimers producing rich long-range anisotropic dipole-dipole interactions. By use of the broad Feshbach resonance situated at 834G we associate fermionic lithium-6 atoms into bosonic lithium-6-2 Feshbach molecules. Subsequent evaporative cooling drives a phase transition in the diffuse lithium gas to produce a molecular Bose-Einstein Condensate containing up to 1e4 atoms, the first to be produced in the UK. This thesis documents the construction of the quantum integrated light and matter interface (QuILMI) in its entirety from inception to realisation. An enormous amount of work has gone into the design and subsequent development of various vacuum, laser and magnetic systems that work seamlessly in tandem via a programmable control system. The system is now in a position to demonstrate to the world that atom-photon coupling on a chip is the way forward. For the lithium-caesium mixture experiment, a versatile dual-species oven has been meticulously designed, constructed and thoroughly characterised to replace one that significantly malfunctioned and harmed the experiment. The oven is capable of tuning the axial fluxes of lithium and caesium through several orders of magnitude via PID temperature controlled reservoirs. An array of fifteen 0.51mm diameter microtubes highly collimate the dual-species atomic beam such that little flux is wasted prolonging the life of both the source and the vacuum ion pumps. This source will return the system to its former glory such that the ultimate goal of realising ultracold lihtium-caesium Feshbach molecules can once again be pursued.
47
Almalki, Shaimaa. "Nano-engineering of High Harmonic Generation in Solid State Systems." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39308.
Full textAbstract:
High harmonic generation (HHG) in solids has two main applications. First, HHG is an all-solid-state source of coherent attosecond very ultraviolet (VUV) radiation. As such, it presents a promising source for attosecond science. The ultimate goal of attosecond science is to make spatially and temporally resolved movies of microscopic processes, such as the making and breaking of molecular bonds. Second, the HHG process itself can be used to spatially and temporally resolve fast processes in the condensed matter phase, such as charge shielding, multi-electron interactions, and the dynamics and decay of collective excitations. The main obstacles to realize these goals are: the very low efficiency of HHG in solids and incomplete understanding of the ultrafast dynamics of the complex many-body processes occurring in the condensed matter phase. The theoretical analysis developed in this thesis promises progress along both directions. First, it is demonstrated that nanoengineering by using lower-dimensional solids can drastically enhance the efficiency of HHG. The effect of quantum confinement on HHG in semiconductor materials is studied by systematically varying the confinement width along one and two directions transverse to the laser polarization. Our analysis shows growth in high harmonic efficiency concurrent with a reduction of ionization. This decrease in ionization comes as a consequence of an increased band gap resulting from the confinement. The increase in harmonic efficiency results from a restriction of wave packet spreading, leading to greater re-collision probability. Consequently, nanoengineering of one and two-dimensional nanosystems may prove to be a viable means to increase harmonic yield and photon energy in semiconductor materials driven by intense laser fields. Thus, it will contribute towards the development of reliable, all-solid-state, small-scale, and laboratory attosecond pulse sources.
Second, it is shown that HHG from impurities can be used to tomographically reconstruct impurity orbitals. A quasi-classical three-step model is developed that builds a basis for impurity tomography. HHG from impurities is found to be similar to the high harmonic generation in atomic and molecular gases with the main difference coming from the non-parabolic nature of the bands. This opens a new avenue for strong field atomic and molecular physics in the condensed matter phase and allows many of the processes developed for gas-phase attosecond science to be applied to the condensed matter phase. As a first application, my conceptual study demonstrates the feasibility of tomographic measurement of impurity orbitals. Ultimately, this could result in temporally and spatially resolved measurements of electronic processes in impurities with potential relevance to quantum information sciences, where impurities are prime candidates for realizing qubits and single photon sources.
Although scanning tunneling microscope (STMs) can measure electron charge distributions in impurities, measurements are limited to the first few surface layers and ultrafast time resolution is not possible yet. As a result, HHG tomography can add complementary capacities to the study of impurities.
48
Werwa, Eric 1970. "The role of quantum confinement effects in the visible photoluminescence from silicon nanoparticles." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/43547.
Full text
49
Kempf, James G. "Probing quantum confinement at the atomic scale with optically detected nuclear magnetic resonance." Diss., Pasadena, Calif. : California Institute of Technology, 2001. http://resolver.caltech.edu/CaltechETD:etd-08282001-123851.
Full text
50
Rieländer, Daniel. "Quantum light source compatible with solid-state quantum memories and telecom networks." Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/404382.
Full textAbstract:
This PhD thesis is in the scope of experimental quantum communication. It deals with correlated photon pairs of which one photon is stored in a solid state device, while the other photon is at telecom wavelength. Quantum correlation between a photon at telecom wavelength and a photon stored in a quantum memory is an important resource for future applications like quantum repeaters, allowing the transmission quantum states over long distances.
During the first part of this thesis, a novel photon pair source has been developed, based on spontaneous parametric downconversion (SPDC) inside a bow-tie cavity. SPDC is a non-linear process which splits a pump photon sporadically into two correlated photons, called signal and idler photon. The source used in this work has been designed to be compatible with a solid state quantum memory based on a Praseodymium doped crystal, using the atomic frequency comp (AFC) protocol. This material has shown promising properties for classical light storage. However, it features a small storage bandwidth of 4 MHz at 606 nm, which sets stringent requirements for the photons to be stored. To match these requirements the SPDC process takes place inside a bowtie cavity which is resonant with the created signal and idler photons. The difference between storage wavelength and telecom wavelength (1436 nm in our case) leads to widely non-degenerate photon pairs. These double resonance leads to a strong clustering effect, which suppresses a high number of redundant spectral modes. The created photon spectrum is investigated carefully and consists of three clusters with few well separated modes. The width of each mode is around 2 MHz and matches the requirement for the quantum memory. Single mode operation was achieved by placing an additional Fabry-Perot cavity in the idler field at 1436 nm. This resulted in the demonstration of the narrowest photon pairs consisting of a spectral single mode, created by SPDC to date.
In the second part of the thesis, heralded single photons at 606 nm were created by the detection of a photon at 1436 nm. These heralded photons were then stored as collective optical excitations in a praseodymium crystal, using the AFC scheme. Non-classical correlation between the heralding photon and the stored and retrieved photons were observed for storage time up to 4 µs, 20 times longer than achieved in previous solid state quantum memory experiments.
Further development on the source, led to improved results, including an increase of coincidence count rate by one order of magnitude and a heralding efficiency of 28 %. The single photon nature of the heralded photon was also measured directly by showing strong antibunching of the 606 nm signal field. These improvements made the created photons compatible with the storage in the spin state of the praseodymium level scheme, using the full AFC protocol. That enabled an extended storage time of 11 µs with on demand readout of the stored photon.
The last part of the thesis explores another important resource for the distribution of quantum states with a quantum repeater, entanglement between the created photon pairs. Here we show a rather new approach of entanglement, which is well suited for narrow band photons based on frequency bins. We take advantage of the fact that the source naturally creates several energy correlated well separated frequency modes. In order to show the coherent superposition of the frequency modes, we use electro-optical modulators to coherently mix them. We could show high-visibility two-photon interference fringes, a strong indicator for entanglement in the frequency domain.
The results presented in this thesis open the door for the demonstration of entanglement between a solid-state spin-wave quantum memory and a photon at telecom wavelength. This represents an important step for the realization of quantum repeaters using solid state resources.<br>Esta Tesis doctoral se encuentra en el área de la comunicación cuántica experimental. Trata de pares de fotones de los cuales uno está almacenado en una memoria cuántica de estado sólido y su pareja es compatible con redes telecom. Las correlaciones cuánticas entre un fotón telecom y un fotón almacenado en una memoria cuántica son un recurso importante para aplicaciones del futuro como un repetidor cuántico, que permite la transmisión de un estado cuántico hacia distancias largas. Durante la primer parte de la tesis, se ha desarrollado una fuente de fotones nueva basada en la conversión paramétrica espontanea (SPDC). SPDC es un proceso no lineal que divide esporádicamente un fotón de alta frecuencia en dos fotones correlacionados de baja frecuencia dentro de un rango de varios centenares de GHz, llamados fotones signal y idler. La fuente es compatible con una memoria cuántica de estado sólido basada en un cristal dopado con iones de praseodimio, usando el protocolo de pinta de frecuencias atómica (AFC). Este material ha demostrado propiedades extraordinarias para el almacenamiento de luz coherente. Sin embargo, ofrece un ancho de banda muy limitado de 4 MHz alrededor de una longitud de onda de 606 nm para el almacenamiento. Esto pone requisitos rigurosos a los fotones creados. Para cumplir con estos requisitos el proceso de SPDC se encuentra dentro de una cavidad de configuración ¿bow-tie¿. La cavidad es resonante con los fotones de signal y los de idler, que tienen longitudes de onda diferentes, que induce pares de fotones extensamente no-degenerados. Esta resonancia doble induce un fuerte efecto de agrupación de modos espectrales, que evita un gran número de modos redundantes. El espectro de los fotones creados se ha investigado detenidamente y contiene tres grupos con pocos modos espectrales. La anchura de cada modo es 2 MHz y cumple con los requisitos de la memoria cuántica. El filtraje de un modo único se realiza con una cavidad de Fabry-Perot adicional. El resultado es la demonstración de los pares de fotones más estrechos en un modo espectral individual creados por SPDC. En la segunda parte de la tesis se crean fotones individuales de 606nm anunciados por la detección de un fotón de 1436 nm. Estos fotones anunciados se almacenan como excitación colectiva óptica en un cristal de praseodimio usando el protocolo de AFC. Correlaciones no-clásicas entre el fotón almacenado y el fotón anunciante se observan hasta una duración de almacenado de 4 µs, 20 veces más largo que lo conseguido en experimentos previos con una memoria cuántica de estado sólido. Con el desarrollo posterior de la fuente se logró una tasa de coincidencia un orden de magnitud más alta y una eficiencia de anunciado del 28 %. La naturaleza del fotón individual anunciado se demostró por medido del "antibunching" del campo signal. Estos avances hicieron que los fotones creados fueran compatibles con el almacenamiento en el estado de spin del cristal de praseodimio usando el protocolo completo de AFC. Esto permitió que la duración de almacenamiento fuera extendida a 11 µs y también una lectura en demanda. La última parte de la tesis explora entrelazamiento en frecuencia entre los pares de fotones creados. Es un tipo de entrelazamiento, aún poco investigado, basado en los modos espectrales, que es muy conveniente para los fotones de banda estrecha. Tomamos la ventaja de que la fuente crea varios modos de frecuencias separados y correlacionados en energía. Para demonstrar una superposición coherente de los modos de frecuencia usamos moduladores electro-ópticos para mezclarlos coherentemente. Demostramos franjas de interferencia entre dos fotones con una alta visibilidad, un fuerte indicador del entrelazamiento en frecuencia.