Academic literature on the topic 'Atomic magnetometry'

Thesis (M.S.)--Boston University<br>Coherent population trapping (CPT) effects can be realized with frequency mod- ulated lasers and compact vapor cells of alkali metals such as Rubidium-87. Using these optical resonances, one can readily measure the hyperfine separation of this three-level atom. In the presence of a magnetic field, the Zeeman effect causes magnetic sublevels of these hyperfine ground states to split; the frequency of such splitting can be measured in an ensemble of Rubidium atoms with the magnetometer we have constructed. While other groups have constructed magnetometers based on these effects, none to our knowledge have investigated the capability to measure magnetic fields remotely. Most atomic-optical magnetometers,colocate the transmit and receive optical system with the vapor cell itself or require fiber optics at the location of the cell; our free-space technique with a reflective geometry lends itself to measurement at distances greater than could be achieved with those methods. We have developed a laboratory FM laser spectrometer that interrogates CPT resonances to measure magnetic fields with the vapor cell not necessarily co-located with the spectrometer. Its intrinsic linewidth (in the presence of transit-time broadening) is less than 30 kilohertz, which allows measurements on the order of 2 microtesla. We present results concerning the accuracy of the magnetometer at about one meter of standoff distance, and describe considerations for measurements at longer distances.

The nitrogen-vacancy (NV) center in diamond is a solid-state point defect with an electronic spin that has accessible quantum mechanical properties. At room temperature, the electronic ground state sub-levels of the NV center can be initialized and read out using optical pumping, as well as coherently controlled using microwave frequency fields. This thesis focuses on using the spin state of the NV center for highly-sensitive magnetometry under ambient conditions. In particular, when the diamond surface is properly prepared, we demonstrate that NV centers can be used to measure the magnetic fluctuations stemming from individual molecules and ions attached or adsorbed to the surface. This thesis begins by introducing the physical and electronic structure of the NV center at room temperature, followed by the fundamental measurements that allow us to use the NV center as a sensitive magnetometer. Combining our sensitive NV center magnetometer with techniques from chemistry and atomic force microscopy (AFM), we demonstrate the all-optical detection of a single-molecule electron spin at room temperature. Finally, we discuss the time-resolved detection of individual electron spins adsorbing onto the surface of nano-diamonds. By extending our techniques to nano-diamonds, we move closer towards \textit{in vitro} magnetic field sensing that could be pivotal for better disease diagnosis and drug development.<br>Engineering and Applied Sciences - Applied Physics

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2011.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 27).<br>The nitrogen-vacancy (N-V) center in diamonds have the potential to be an ultra-sensitive magnetic field sensor that is capable of detecting single spins. Implementing this sensor for general and nontransparent samples is not trivial. For N-V centers to be a useful probe, a way of positioning the NV center with nanometer accuracy while simultaneously measuring its fluorescence is needed. Here, a method of using N-V centers as magnetometer probes by combining this sensor with Atomic Force Microscopy (AFM) is described. A custom AFM was built that allows optical monitoring of the cantilever tip and collection of fluorescence with a high-NA objective from the same side. The AFM has a large open bottom and top and thus provides dual optical access. The motion of the cantilever is measured by optical beam deflection so that a wide range of commercial cantilevers can be used. The AFM and the confocal microscope objective can be locked in position while a piezoelectric stage allows raster scanning of the substrate.<br>by Kevin Kai Chang.<br>S.M.

The development of an experimental apparatus to produce Bose-Einstein condensates (BECs) of 87Rb atoms and their application to magnetometry are discussed. Optical detection of atomic Larmor precession is a widely explored method for high-sensitivity measurements of magnetic fields. In this context, short laser/atom interaction time, atomic thermal diffusion and decoherence effects are among the main limitations. In this thesis, we overcome such problems by using spin-polarised 87Rb ultra-cold atoms as the sensing element. After the atoms are polarised, a resonant pulse of radio-frequency excites Larmor precession, which is sensitive to external magnetic fields. By measuring the perturbations of the radio-frequency induced spin precession, information on the magnetic fields of interest. This is achieved by monitoring the polarisation plane’s rotation of a linearly polarised resonant laser probe. In the first part of this thesis, the building and optimisation of a laser-cooling set up to obtain a BEC in a hybrid trap is reported. In order to achieve the Phase Space Density (PSD) required for BEC, several different stages of trapping and cooling are necessary. Each phase has been implemented and optimised. The first step consists in the magneto-optical trap (MOT). Here a velocity dependent damping force and a spatially dependent confining force give the largest changes in PSD. Then atoms are loaded into a hybrid trap obtained by overlapping a quadrupole magnetic potential and a far detuned optical crossed dipole trap. The final stage for the condensation consists of forced evaporative cooling, both via magnetic and optical evaporation. In the second part of the thesis, a general overview of the principles of optical atomic magnetometry is provided and the advantages of using ultra-cold atoms with respect to conventional thermal vapours are discussed. The implementation, operation and a preliminary characterisation of the ultra-cold atom magnetometer are described along with the preliminary results collected. Finally, a plan for future improvements of its sensitivity is presented.

Observing and controlling solid state quantum systems is an area of intense research in quantum science today. Such systems offer the natural advantage of being bound into a solid device, eliminating the need for laser cooling and trapping of atoms in free space. These solid state "atoms" can interface directly with photonic channels designed to efficiently couple into larger networks of interacting quantum systems. With all of the tools of semiconductor fabrication technology available, the idea of scalable, chip-based quantum networks is a tantalizing prospect.<br>Physics

Un moment dipolaire électrique permanent (EDM) est une propriété fondamentale des systèmes simples comme par exemple l'électron, les atomes/molécules ou le neutron dont l'existence est prédite par le Modèle Standard de la physique des particules (MS) mais qui n'a pas pour l'heure jamais été observée. Cette observable violant la symétrie CP offre la possibilité de relier la physique des particules à l'énigme cosmologique fondamentale de l'asymétrie baryonique de l'Univers observée de nos jours. Produire une telle asymétrie requiert de nouvelles sources/de nouveaux mécanismes de violation de CP, hors MS, qui peuvent être sondés de façon privilégiée par les recherches d'EDM. La sensibilité des expériences EDM actuelles se trouve des ordres de grandeurs au-dessus des prédictions du secteur faible du MS. L'absence de signal, après 60 ans de quête, détermine la limite supérieure la plus forte sur la violation de CP dans le secteur fort du MS et contraint l'espace des phases des modèles de nouvelle physique. A contrario, la mesure d'un EDM non nul dans les années à venir pourra s'interpréter comme le signal d'une physique au-delà du MS évoluant à l'échelle multi-TeV. Dans cette perspective envoûtante, de nombreux nouveaux projets de mesures des EDM ont vu le jour ces dernières années et d'importants efforts sont poursuivis auprès du neutron notamment. Ce manuscrit présente la recherche de l'EDM du neutron menée auprès de l'expérience la plus sensible à ce jour basée à l'Institut Paul Scherrer en Suisse<br>A permanent electric dipole moment (EDM) is a fundamental property of simple systems such as the electron, atoms/molecules or the neutron whose amplitude is expected to be non-zero within the Standard Model of particles physics (SM) but which has never been observed so far. This observable violating the CP symmetry offers the opportunity to link particle physics to the fundamental cosmological enigma of the observed baryon asymmetry of the Universe. Such an asymmetry requires new CP violation sources/mechanism beyond the SM, which can be best probed by EDM searches. The current EDM experiments sensitivity is order of magnitude above the weak SM sector predictions. Measuring a null EDM, after a 60 years quest, set the strongest upper limit on the CP violation in the strong SM sector and constrains the new physics models phase space. On the contrary, measuring a non-zero EDM in the coming years can be understood as a signal from physics beyond the SM evolving at a multi-TeV scale. In this haunting perspective, many new EDM projects raised in the last years and important efforts are pursued near the neutron in particular. This manuscript present the neutron EDM search near the most sensitive experiment running at the Paul Scherrer Institute in Switzerland

An atomic magnetometer is a sensor which is used to measure a magnetic field through its interaction with the atomic sample. Significant research into atomic magnetometry has led to the development of very sensitive atomic sensors capable of matching the sensitivity of the most sensitive magnetometers, superconducting quantum interference devices (SQUIDs). Because SQUIDS require cryogenics to operate, atomic magnetometers provide a sensitive, yet low-cost alternative. They have found use in many areas such as medicine, security, explosives detection and fundamental physics research. One of the primary factors influencing sensitivity is the detuning of the probe beam from the resonant transitions of the atomic ground state. A caesium room temperature radio-frequency (rf) magnetometer is constructed and used to investigate the influence of the probe beam detuning on the magnetometer signal of the F = 3 and F = 4 ground states. The results of probing near and far from resonance revealed an off-resonant regime and two absorptive regimes. In the off-resonant regime, the atomic spins are unperturbed by the probe beam; it is a quantum non-demolition (QND) interaction. The two absorptive regimes, found when the probe beam is in the vicinity of either the 62S1 2 F = 3 → 6 2P3 2 F 0 = 2,3,4 or the 62S1 2 F = 4 → 6 2P3 2 F 0 = 3,4,5 transitions, is characterised as a non-QND interaction in which the probe beam influences the measurement. The sensitivity of the rf magnetometer is determined to be ≈ 1.98 fT/ √ Hz. In addition, the exploration of the relationship between the signal to noise ratio (SNR) and probe beam detuning revealed that the SNR is constant with detuning but the larger the detuning, the higher the probe beam power needs to be to reach the optimum SNR.

Cette thèse traite de la magnétométrie dans le cadre de la mesure du moment électrique dipolaire du neutron avec le spectromètre RAL/Sussex/ILL. En particulier, le co-magnétomètre mercure, pré-existant, a été modélisé et optimisé en vue de son utilisation pour les prochaines mesures au Paul Scherrer Institut (Villigen, Suisse) en 2010-2012. Sur la base de données prises à l'Institut Laue-Langevin (Grenoble, France), la complémentarité entre la magnétométrie externe césium et la co-magnétométrie mercure a été étudiée. Un tel système de double magnétométrie est unique. Cette étude débouche sur une méthode permettant un meilleur controle des erreurs systématiques liées au co-magnétomètre mercure et sur une nouvelle contrainte sur des couplages exotiques du neutron libre violant l'invariance de Lorentz<br>In this thesis, magnetometry is studied in the context of the neutron Electric Dipole Moment (nEDM) measurement with the RAL/Sussex/ILL spectrometer. In particular, the pre-existing mercury co-magnetometer has been modeled and optimized to be used in the next nEDM measurement at the Paul Scherrer Institut (Villigen Suisserland) in 2010-2012. Using data taken at the Institut Laue-Langevin (Grenoble, France), the complementarity between external cesium magnetometry and mercury co-magnetometry has been studied, bringing two results : - a best way to control systematics due to the co-magnetometer - a limit on the neutron anomalous couplings that violates Lorentz invariance