Magnetism plays a fundamental role in nature existing in almost every conceivable domain of the physical world ranging from stars and planets to our brains and hearts. Some magnetic phenomena are easy to observe and measure, whilst others are small and subtle making them almost impossible to detect. Developments in precision magnetometry, utilising the quantum nature of atoms has given access to the world of small and subtle enabling the understanding of such signals as well as pushing the boundaries of knowledge of the fundamental forces of nature. In this thesis we describe theoretical and experimental methods to dispersively detect all three vector components of an external magnetic field using radio-frequency dressed alkali atoms based on the Voigt effect. To achieve this, we measure the linear birefringence of the radio frequency dressed atomic medium via polarization homodyning. This gives rise to modulated polarization signals at the first and second harmonic of the dressing frequency. The vector components of the external magnetic field are mapped onto the quadratures of these harmonics. Our scheme requires only one frequency of modulation and has a simple single axis beam geometry making it advantageous for miniature magnetic field sensors. Furthermore, we extend our Voigt effect scheme to dressed microwave spectroscopy and show that it can be used to infer the prepared state populations paving the way towards partial quantum state tomography.
Magnetism plays a fundamental role in nature existing in almost every conceivable domain of the physical world ranging from stars and planets to our brains and hearts. Some magnetic phenomena are easy to observe and measure, whilst others are small and subtle making them almost impossible to detect. Developments in precision magnetometry, utilising the quantum nature of atoms has given access to the world of small and subtle enabling the understanding of such signals as well as pushing the boundaries of knowledge of the fundamental forces of nature. In this thesis we describe theoretical and experimental methods to dispersively detect all three vector components of an external magnetic field using radio-frequency dressed alkali atoms based on the Voigt effect. To achieve this, we measure the linear birefringence of the radio frequency dressed atomic medium via polarization homodyning. This gives rise to modulated polarization signals at the first and second harmonic of the dressing frequency. The vector components of the external magnetic field are mapped onto the quadratures of these harmonics. Our scheme requires only one frequency of modulation and has a simple single axis beam geometry making it advantageous for miniature magnetic field sensors. Furthermore, we extend our Voigt effect scheme to dressed microwave spectroscopy and show that it can be used to infer the prepared state populations paving the way towards partial quantum state tomography.
We describe a method to dispersively detect all three vector components of an external magnetic field using alkali atoms based on the Voigt effect. Our method relies on measuring the linear birefringence of the radio frequency dressed atomic medium via polarization homodyning. This gives rise to modulated polarization signals at the first and second harmonic of the dressing frequency. The vector components of the external magnetic field are mapped onto the quadratures of these harmonics. We find that our scheme can be utilised in both cold and hot atomic gases to detect such external fields in shielded and unshielded environments. In the shielded hot vapour case we achieve field sensitivities well below 1~pT/√ Hz range for all 3 vector components, using pump-probe cycles with 125 Hz repetition rate, and limited by the short coherence time of the cell. Finally, our scheme has a simple single axis beam geometry making it advantageous for miniature magnetic field sensors.
We describe a method to dispersively detect all three vector components of an external magnetic field using alkali-metal atoms based on the Voigt effect. Our method relies on measuring the linear birefringence of the radio-frequency dressed atomic medium via polarization homodyning. This gives rise to modulated polarization signals at the first and second harmonic of the dressing frequency. The vector components of the external magnetic field are mapped onto the quadratures of these harmonics. We find that our scheme can be utilized in both cold and hot atomic gases to detect such external fields in shielded and unshielded environments. In the shielded hot vapor case we achieve field sensitivities in the pT/Hz range for all three vector components, using pump-probe cycles with 125-Hz repetition rate, and limited by the short coherence time of the cell. Finally, our scheme has a simple single axis beam geometry, making it advantageous for miniature magnetic-field sensors.
We present the results of stroboscopic microwave spectroscopy of a radio-frequency-dressed optically pumped magnetometer. The interaction between radio-frequency-dressed atoms and a synchronously pulsed microwave field followed by Voigt-effect-based optical probing allows us to perform a proper ground-state interrogation for dressed state and assess the efficiency of the state preparation process. This work shows that through the stroboscopic technique the microwave spectrum is simplified when compared to the continuous counterpart. This is a necessary step towards investigating vector magnetometers in unshielded environments, where the influence of the nonlinear Zeeman effect, a source of heading errors, would otherwise be spectrally unresolved in dressed states. To theoretically describe the system, we solve the dynamical equation of the density matrix employing Floquet expansion. Our theoretical results are in good agreement with experimental measurements over a wide range of parameters and pumping conditions.
Quantum optical sensing is a maturing field that offers the capability to achieve extraor- dinary sensitivity. Atomic magnetometers, for example, now have the capability to detect brain signals and to precisely measure Earth’s gravity field. In optical atomic magnetome- ters, the electronic spins of the atoms in vapor form are aligned in the same direction by “pumping” the ensemble using laser light at a select frequency. Any magnetic field alters the spin states, which changes the optical properties of the vapor, such as the transmission of the laser light, providing a way to measure magnetic fields. After reviewing the theory of atomic structure and atom-light interactions relevant to the research presented here, I describe in the first part of this thesis a vector magnetometry method using microwave-assisted optical pumping, in which a microwave field resonant to the ground state hyperfine splitting of 87Rb pumps an ensemble of warm rubidium vapor, in addition to a strong optical pump beam, and a weaker optical probe beam. I present theoretical details as well as preliminary data demonstrating magnetic field measurements of a DC magnetic field. The measurements were taken when the DC field was aligned at various angles relative to the microwave magnetic field alignment. I compare theoretical and experimental differences in the measurements. With new methods for quantum devices comes the need for portability. In the second part of this thesis, we demonstrate the fabrication of millimeter-sized rubidium vapor cells using silicon micro-machining techniques. This method is relatively inexpensive compared to glass-blowing methods and allows rapid, large-scale production. I describe our process flow and demonstrate the presence of rubidium atoms inside our vapor cells. To conclude, suggestions for improvement are discussed.
Spin polarized atomic magnetometers involve the preparation of atomic spins and their detection for monitoring magnetic fields. Due to the fact that magnetic fields are ubiquitous in our world, spin polarized atomic magnetometers are used in a wide range of applications from the detection of magnetic fields generated by the human heart and brain to the detection of nuclear magnetic resonance. In this thesis we developed microfabricated spin polarized atomic magnetometers. These sensors are based on optical pumping and spin-exchange collisions between alkali atoms and noble gases contained in microfabricated millimeter-scale vapor cells. In the first part of the thesis, we improved different features of current microfabricated optical magnetometers. Specifically, we improved the bandwidth of these devices, without degrading their magnetic field sensitivity, by broadening their magnetic resonance through spin-exchange collisions between alkali atoms. We also implemented all-optical excitation techniques to avoid problems, such as the magnetic perturbation of the environment, induced by the radio-frequency fields used in some of these sensors. In the second part of the thesis we demonstrated a microfluidic chip for the optical production and detection of hyperpolarized Xe gas through spin-exchange collisions with optically pumped Rb atoms. These devices are critical for the widespread use of spin polarized atomic magnetometers in applications requiring simple, compact, low-cost, and portable instrumentation.
As is well known a linearly polarized resonant laser will cause atoms to generate a magnetic tensor moment (MTM) by polarizing them. When there exists an external magnetic field, it is possible that the moment will precess around the field. In the presence of a radio frequency (RF) exciting source, we investigate theoretically the dependence of time-independent (direct current, DC), the first and second harmonic signal of the MTM precession on magnetic vector field, and obtain its analytical solution by solving the Liouville equation. The results show that the interference of both harmonic components will result in the precession spectrum evidently varying. A detailed explanation is described in the following. For the DC signal, Rabi frequency Ω of 1/(2√2) is a spectral splitting threshold. When it is greater than the threshold, the interference will cause single resonant absorption dip characterized usually to split into two dips, which has not been reported before to the best of our knowledge, and the separation between both the dips may be expressed as √3√Ω2+Ω4 -Ω2-1. For the first harmonic signal including symmetric and antisymmetric component, an interference fringe will appear near the center of antisymmetric part when Ω >1/(2√2), simultaneously its symmetric part behaves like the above dc component, such as splitting threshold and separation between both dips. With regard to the second harmonic signal, it is found that the interference can also lead to the width of the second harmonic decreasing to 38% compared with the case of the first harmonic signal. At the optimum RF Rabi frequency, on the assumption that noise spectral density is constant, it is theoretically shown that the most sensitive magnetometer, realized by the DC component or the first or second harmonic signal of the precession, depends only on the angle between the light polarization and the measured magnetic field.In fact, we are able to obtain the modules of the measured magnetic vector by RF resonant frequency. The angle between the magnetic field and the laser polarization is determined just by the ratio of the intensity of the DC component to the intensity of the second harmonic signal and the ratio between the intensities of the symmetric parts of two harmonic signals in resonance, and another orientation angle between the measured field projection at the plane perpendicular to the light polarization and the direction of RF source depends on the phase difference between the antisymmetric components of both harmonic signals. Consequently, we demonstrate a vectorial atomic magnetometer that is realized by using the RF source and the linearly polarized resonant laser without rotating laser polarization. This kind of atomic magnetometer with simple sensor structure is easy to integrate vector magnetometer array which will be suitable for solving the inverse problem and geomagnetic navigation.