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Sensors

Precision Magnetic Field Sensing with Dual Multi-Wave Atom Interferometer

Wenhua Yan, Xudong Ren, Min-Kang Zhou, Zhong-Kun Hu

Published Dec 24, 2022• 4 citations
Publisher

Abstract

Precision magnetic field measurement is widely used for practical applications, fundamental research, and medical purposes, etc. We propose a novel quantum magnetometer based on atoms' multi-wave (3-wave and 5-wave) Ramsey interference. Our design features high phase sensitivity and can be applied to in situ measurements of the magnetic field inside vacuum chambers. The final state detection is designed to be achieved by Raman's two-photon transition. The analytical solution for applicable interference fringe is presented. Fringe contrast decay due to atom temperature and magnetic field gradient is simulated to estimate reasonable experimental conditions. Sensitivity functions for phase noise and magnetic field noise in a multi-wave system are derived to estimate the noise level required to reach the expected resolution. The validity of the model, dual-channel features on bias estimation, and the quasi-non-destructive detection feature are discussed.

DOI
10.3390/s23010173

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Saeed Hamzeloui

Atomic interferometry is a very sensitive technique in precision measurements. In this PhD work we explore ways to improve certain aspects of atomic interfer- ometry. We show that there are some advantages on using magnetic sensitive states. We introduce the required infrastructures to implement Ramsey type interferometry on particular transitions. Using a Magneto Optical Trap (MOT) which is the main prerequisite, the atoms are trapped and cooled. The trapping procedure with the MOT requires ingredients such as lasers, the homogeneous and inhomogeneous magnetic fields, the chamber containing the sample, the vacuum system and the detection part (see Chapter 2). At the beginning of my PhD, this facility for trapping the rubidium atoms was available. Later on we upgraded the vacuum system. During this PhD work we could further cool down the trapped sample thanks to the optical molasses technique. We maintain the atoms at temperatures typically below some tenths of micro Kelvin. The coherent manipulation of the atoms is the significant part of this thesis since we aim to do atomic interferometry. Using radiations in microwave domain, it is feasible to couple any two states and do the Rabi oscillations between the hyperfine and Zeeman levels.\nMy first work as a PhD student was to contribute in the Dual Isotope MOT (DIMOT) experiment (see Chapter 3). The idea was to trap both isotopes of rubidium simultaneously by using only single laser and an Electro-Optical Modulator (EOM). This work introduces huge simplifications on the optical part and is extendable to trap more isotopes at the same time. The experiment has the optical and RF parts and my contribution was to complete the RF part.\nStarting all the atoms at the particular initial point for the interferometry takes us some considerable time to be sure that we correctly transfer the atomic population into the desired state (see the discussion in Chapter 4). From that point we focused on two transitions to use the Ramsey type interferometer. Each of these two transitions have an optimum operating point in order to be far from the magnetic field fluctuations since the interferometers are quite sensitive to the field perturbations sensed from the environment. At the end we aim to combine these two transitions of interest to make a dual interferometer (see Chapter 6). The idea is to obtain the minimum magnetic sensitivity at a tunable magnetic field by changing the fraction of atoms in each interferometer. The dual interferometer may be useful in applications where low magnetic sensitivity is required at a particular magnetic field.

•Jan 1, 2016•0 citations
Precision magnetic field measurement is widely used for practical applications, fundamental research, and medical purposes, etc. We propose a novel quantum magnetometer based on atoms' multi-wave (3-wave and 5-wave) Ramsey interference. Our design features high phase sensitivity and can be applied to in situ measurements of the magnetic field inside vacuum chambers. The final state detection is designed to be achieved by Raman's two-photon transition. The analytical solution for applicable interference fringe is presented. Fringe contrast decay due to atom temperature and magnetic field gradient is simulated to estimate reasonable experimental conditions. Sensitivity functions for phase noise and magnetic field noise in a multi-wave system are derived to estimate the noise level required to reach the expected resolution. The validity of the model, dual-channel features on bias estimation, and the quasi-non-destructive detection feature are discussed.
We report an experimental study of magnetic-field-sensitive multi-wave interference, realized in a three-wave RF-atom system. In the F = 1 hyperfine level of the 87Rb 52S1/2 ground state, Ramsey fringes were observed via the spin-selective Raman detection. A decrease in the fringe contrast was observed with increasing free evolution time. The maximum evolution time for observable fringe contrasts was investigated at different atom temperatures, under free-falling and trapped conditions. As the main interest of the Ramsey method, the improvement in magnetic field resolution is observed with an increase of evolution time T up to 3 ms and with the measurement resolution reaching 0.85 nT. This study paves the way for precision magnetic field measurements based on cold atoms.
Atoms in magnetically sensitive sublevels constitute a natural sensor for absolute magnetic field measurements, which are explored here to form an optical Ramsey interferometer for determining the magnetic field distribution. An optical Ramsey atom interferometer provides a convenient way to map a magnetic field in vacuum. In comparison with the often used Raman spectroscopy method, a Ramsey interferometer can not only improve the sensitivity, but also dramatically suppress the contribution of the ac Stark effect. Furthermore, in this work, the magnetically sensitive atoms are velocity-selected, which improves the spatial resolution for the magnetometer as well as the contrast of the Ramsey fringes. A short-term sensitivity of 1.4nT/Hz1/21.4\phantom{\rule{0.2em}{0ex}}{\mathrm{nT/Hz}}^{1/2}1.4nT/Hz1/2 for magnetic field measurement is finally achieved even with an interrogation time as short as $500\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{s}$. The presented approach for absolute magnetic field measurement is expected to find wide applications in atom-interferometry-based precision measurements.
We implement a magnetic-field-sensitive multiwave atom Ramsey interferometer based on radio-frequency (RF) field-coupled Zeeman states, and we theoretically derive and experimentally measure its frequency-domain transfer function with low-pass filtering characteristics. In addition, we investigate a potential application scheme of the transfer functions for interference fringe recovery. As the measurements involve the ac magnetic field, a Raman spectrum-based solution is implemented to calibrate the actual ac magnetic field amplitude at the position of the atom inside the vacuum chamber. The methods demonstrated in this work will help to improve the performance of the atom interferometer and are also useful in Ramsey interference-based systems and spinor Bose-Einstein condensates (BEC) experiments.
Magnetic field sensing utilizing Bose-condensed atomic gases can achieve both high sensitivity and spatial resolution. Employing two-photon transitions from F=1, mF=1→F=2, mF=-1 (F is the quantum number of total atomic angular momentum, mF is the magnetic quantum number of F level) of Bose-condensed 87Rb atomic gases in one-dimensional optical lattice, the precision magnetic field measurement with phase Ramsey interference has been demonstrated. Utilizing single-photon transitions from F=1, mF=1→F=2, mF=0 of Bose-condensed 87Rb atomic gases in a crossed optical dipole trap, we experimentally study frequency domain Ramsey interference, time domain Ramsey interference, and phase domain Ramsey interference. Based on phase Ramsey interference, the sensitivity and spatial resolution of static magnetic field measurement are evaluated. The comparison of these three typical Ramsey interferences reveals that phase Ramsey interference can effectively avoid the fringe distortion in frequency-domain interference and the decoherence effects in time-domain interference, thereby improving the sensitivity and accuracy of the static magnetic field measurement. Utilizing Bose-condensed 87Rb atomic gases with the volume of 1.31±0.03×10-9 cm3 in an unshielded environment, a sensitivity of 130 nT/Hz for static magnetic fields can be achieved. By reducing the preparation time of the atomic gases and increasing the signal interrogation time, the sensitivity has the potential to be further improved.
Abstract The magnetic field is one of the most fundamental and ubiquitous physical observables, carrying information about all electromagnetic phenomena. For the past 30 years, superconducting quantum interference devices (SQUIDs) operating at 4 K have been unchallenged as ultrahigh-sensitivity magnetic field detectors1, with a sensitivity reaching down to 1 fT Hz-1/2 (1 fT = 10-15 T). They have enabled, for example, mapping of the magnetic fields produced by the brain, and localization of the underlying electrical activity (magnetoencephalography). Atomic magnetometers, based on detection of Larmor spin precession of optically pumped atoms, have approached similar levels of sensitivity using large measurement volumes2, 3, but have much lower sensitivity in the more compact designs required for magnetic imaging applications4. Higher sensitivity and spatial resolution combined with non-cryogenic operation of atomic magnetometers would enable new applications, including the possibility of mapping non-invasively the cortical modules in the brain. Here we describe a new spin-exchange relaxation-free (SERF) atomic magnetometer, and demonstrate magnetic field sensitivity of 0.54 fT Hz-1/2 with a measurement volume of only 0.3 cm3. Theoretical analysis shows that fundamental sensitivity limits of this device are below 0.01 fT Hz-1/2. We also demonstrate simple multichannel operation of the magnetometer, and localization of magnetic field sources with a resolution of 2 mm.
Atomic interferometry is a very sensitive technique in precision measurements. In this PhD work we explore ways to improve certain aspects of atomic interfer- ometry. We show that there are some advantages on using magnetic sensitive states. We introduce the required infrastructures to implement Ramsey type interferometry on particular transitions. Using a Magneto Optical Trap (MOT) which is the main prerequisite, the atoms are trapped and cooled. The trapping procedure with the MOT requires ingredients such as lasers, the homogeneous and inhomogeneous magnetic fields, the chamber containing the sample, the vacuum system and the detection part (see Chapter 2). At the beginning of my PhD, this facility for trapping the rubidium atoms was available. Later on we upgraded the vacuum system. During this PhD work we could further cool down the trapped sample thanks to the optical molasses technique. We maintain the atoms at temperatures typically below some tenths of micro Kelvin. The coherent manipulation of the atoms is the significant part of this thesis since we aim to do atomic interferometry. Using radiations in microwave domain, it is feasible to couple any two states and do the Rabi oscillations between the hyperfine and Zeeman levels.\nMy first work as a PhD student was to contribute in the Dual Isotope MOT (DIMOT) experiment (see Chapter 3). The idea was to trap both isotopes of rubidium simultaneously by using only single laser and an Electro-Optical Modulator (EOM). This work introduces huge simplifications on the optical part and is extendable to trap more isotopes at the same time. The experiment has the optical and RF parts and my contribution was to complete the RF part.\nStarting all the atoms at the particular initial point for the interferometry takes us some considerable time to be sure that we correctly transfer the atomic population into the desired state (see the discussion in Chapter 4). From that point we focused on two transitions to use the Ramsey type interferometer. Each of these two transitions have an optimum operating point in order to be far from the magnetic field fluctuations since the interferometers are quite sensitive to the field perturbations sensed from the environment. At the end we aim to combine these two transitions of interest to make a dual interferometer (see Chapter 6). The idea is to obtain the minimum magnetic sensitivity at a tunable magnetic field by changing the fraction of atoms in each interferometer. The dual interferometer may be useful in applications where low magnetic sensitivity is required at a particular magnetic field.