Abstract With the rapid development of atom interferometry, atom interferometers have been widely used in inertial navigation, resource exploration, basic physics and other fields. For precise measurement experiments with multi-loop atom interferometer configuration, it is urgent to establish a high-precision theoretical model charactering the relationship between target measurement quantities and measurement results. Based on this, we adopt the idea of co-moving reference frame, so as to transfer the gravity, gravity gradient and Earth’s rotation effects to the laser light field interacting with atoms by translating, rotating and stretching the background spacetime. With this method, we not only can simplify the analysis process of the experimental principle, but also give the analytical results of the high-order interference phase of the multi-loop atom interferometer containing the gravity gradient and Earth’s rotation. This work will lay a certain theoretical foundation for higher-precision experiment, and will also help to clearly guide the implementation of the experiment.
Abstract With the rapid development of atom interferometry, atom interferometers have been widely used in inertial navigation, resource exploration, basic physics and other fields. For precise measurement experiments with multi-loop atom interferometer configuration, it is urgent to establish a high-precision theoretical model charactering the relationship between target measurement quantities and measurement results. Based on this, we adopt the idea of co-moving reference frame, so as to transfer the gravity, gravity gradient and Earth’s rotation effects to the laser light field interacting with atoms by translating, rotating and stretching the background spacetime. With this method, we not only can simplify the analysis process of the experimental principle, but also give the analytical results of the high-order interference phase of the multi-loop atom interferometer containing the gravity gradient and Earth’s rotation. This work will lay a certain theoretical foundation for higher-precision experiment, and will also help to clearly guide the implementation of the experiment.
Abstract With the rapid development of atom interference technology, multi-loop atom interferometers are widely used in the high-precision measurement of various physical constants and testing of various gravity-related effects. However, in ground-based multi-loop atom interference experiments, the systematic error contribution by classical effects is an important factor that affects the experimental measurement accuracy and gravitational effect detection. Based on this, we used the atomic wave-function evolution-phase accumulation method to provide a high-order interference phase of multi-loop atom interferometers in an inhomogeneous gravitational field containing Earth’s rotation. Furthermore, we propose a new scheme that combines optimised frequency-shift compensation technology with an improved pulse sequence to eliminate systematic errors due to the gravity gradient, Earth’s rotation, and their coupling effect with the pulse duration, as well as the coupling effect of laser detuning with the pulse duration. This study lays a theoretical foundation for experiments on multi-loop atom interferometers with higher precision.
With over 20 years of development, atomic interferometry gravimeters have distinguished themselves in gravity measurements by their high precision and sensitivity. To cater to the demands of field absolute gravity measurements for marine and aerial gravity field measurements, resource exploration, inertial navigation, and positioning, the miniaturization, mobility, and engineering of atomic interferometry gravimeters have become crucial areas of development. On this basis, this article elucidates the principles of atomic interferometry gravimeters, encompassing various laser cooling techniques, magneto-optical traps, and Raman light interference. As a matter of fact, it provides an overview of the principles and achieved precision benchmarks of portable, vehicular, airborne, and shipborne atomic interferometry gravimeters. Additionally, it analyzes the experimental content and results of maritime, terrestrial, and aerial experiments based on portable atomic interferometry gravimeters. The limitations of portable atomic interferometry gravimeters are discussed, along with an exploration of their application prospects. Overall, these results shed light on guiding further exploration of mobile atom interferometry gravity.
A transportable atom interferometer-based gravity gradiometer has been developed at JPL to carry out measurements of Earth's gravity field at ever finer spatial resolutions, and to facilitate high-resolution monitoring of temporal variations in the gravity field from ground- and flight-based platforms. Existing satellite-based gravity missions such as CHAMP and GRACE measure the gravity field via precise monitoring of the motion of the satellites; i.e. the satellites themselves function as test masses. JPL's quantum gravity gradiometer employs a quantum phase measurement technique, similar to that employed in atomic clocks, made possible by recent advances in laser cooling and manipulation of atoms. This measurement technique is based on atomwave interferometry, and individual laser-cooled atoms are used as drag-free test masses. The quantum gravity gradiometer employs two identical atom interferometers as precision accelerometers to measure the difference in gravitational acceleration between two points (Figure 1). By using the same lasers for the manipulation of atoms in both interferometers, the accelerometers have a common reference frame and non-inertial accelerations are effectively rejected as common mode noise in the differential measurement of the gravity gradient. As a result, the dual atom interferometer-based gravity gradiometer allows gravity measurements on a moving platform, while achieving the same long-term stability of the best atomic clocks. In the laboratory-based prototype (Figure 2), the cesium atoms used in each atom interferometer are initially collected and cooled in two separate magneto-optic traps (MOTs). Each MOT, consisting of three orthogonal pairs of counter-propagating laser beams centered on a quadrupole magnetic field, collects up to 10(exp 9) atoms. These atoms are then launched vertically as in an atom fountain by switching off the magnetic field and introducing a slight frequency shift between pairs of lasers to create a moving rest frame for the trapped atoms. While still in this moving-frame molasses, the laser frequencies are further detuned from the atomic resonance (while maintaining this relative frequency shift) to cool the atom cloud's temperature to 2 K or below, corresponding to an rms velocity of less than 2 cm/s. After launch, the cold atoms undergo further state and velocity selection to prepare for atom interferometry. The atom interferometers are then realized using laser-induced stimulated Raman transitions to perform the necessary manipulations of each atom, and the resulting interferometer phase is measured using laser-induced fluorescence for state-normalized detection. More than 20 laser beams with independent controls of frequency, phase, and intensity are required for this measurement sequence. This instrument can facilitate the study of Earth's gravitational field from surface and air vehicles, as well as from space by allowing gravity mapping from a low-cost, single spacecraft mission. In addition, the operation of atom interferometer-based instruments in space offers greater sensitivity than is possible in terrestrial instruments due to the much longer interrogation times available in the microgravity environment. A space-based quantum gravity gradiometer has the potential to achieve sensitivities similar to the GRACE mission at long spatial wavelengths, and will also have resolution similar to GOCE for measurement at shorter length scales.
The measurement of physical quantities and measurement units standard promote the development of metrology. Especially, the developments of laser interference and atomic frequency standard bring a revolutionary leap for metrology. Many precision measurement techniques have been proposed and experimentally demonstrated, such as gravitational wave measurements and laser gyroscopes based on laser interferometry, and atomic clocks and atomic gyroscopes based on the atom interferometry. Recently, a new branch of science, quantum metrology, has grown up to further explore and exploit the quantum techniques for precision measurement of physical quantities.#br#This paper will focus on recent developments in quantum metrology and interference based on coherence and correlation of light and atom. Firstly, we briefly review the development of metrology. Then, we introduce our own researches in recent years, including quantum-correlation SU(1,1) optical interferometer based on four wave mixing process in atomic vapor and the atom-light hybrid interferometer based on Raman scattering in atomic vapor.#br#Interferometer is a powerful tool to measure physical quantities sensitive to the inference wave with high precision, and has been widely used in scientific research, industry test, navigation and guidance system. For example, the laser interferometer is able to measure optical phase sensitive quantities, including length, angular velocity, gravitational wave and so on. Meanwhile, the atom interferometer is sensitive to the change of atomic phase caused by the light, gravity, electric and magnetic fields. As a new type of interferometry, the atom-light hybrid interferometer, is sensitive to both the optical phase and atomic phase. Furthermore, SU(1,1) interferometer and nonlinear atom-light hybrid interferometer have the ability to beat the standard quantum limit of phase sensitivity. Quantum interference technology, whose phase measurement accuracy can break through the limit of standard quantum limit, is the core of quantum metrology and quantum measurement technology.
Abstract We construct a quasi-inertial reference system for the atom interferometer in terms of the light-field compensation, which is equivalent to the establishment of a quantum drag-free system. The compensation considered in our approach involves feedbacks of both classical and quantum nature. As a result, it may significantly reduce the dependence of the interferometric phase shift on the atomic initial position and velocity. As the error bound for gravity experiments originates primarily from the uncertainties in the initial conditions, the proposed quasi-inertial reference system might lead to substantial improvement in this regard. To be specific, the refined process introduced in the present study gives rise to the possibility of the measurement of the Newtonian gravitational constant G beyond the precision level of 10 −6 , as well as the test of the weak equivalence principle beyond 10 −14 . Moreover, when compared with the conventional quasi-inertial reference based on macroscopic objects, additional quantum feedback plays an essential role concerning both theoretical rigor and practical performance enhancement. We further explore the possibility of implementing the proposed quasi-inertial reference system in ongoing experimental developments.
Matter-wave interferometry has enabled high precision measurements of inertial forces such as gravity and the Coriolis force. This is facilitated by the long-term stability of the physical properties of atoms and lasers. Recent experiments have demonstrated the operation of portable, robust sensors using atom interferometry. This has potential uses in the context of inertial navigation, where conventional devices suffer from long-term drifts due to bias instability. Furthermore, determining position via dead reckoning requires minimisation of dead time between measurements. This thesis presents the development of an atom interferometer for measuring horizontal accelerations. In this configuration, gravity induces motion across the laser wavefront, which constrains the tolerable level of wavefront distortions. Effective control of the experiment allows the interferometer to be operated at a rate of 4 Hz. A cold ensemble of 10^6 atoms in the same internal state is prepared in 150 ms. The interferometer operates using a sequence of three laser pulses separated by T= 25 ms to achieve sensitivity to horizontal accelerations. Combining this with a classical accelerometer provides a method of correcting for vibration-induced noise, as well as determining the interferometer fringe order. After an integration time of 40 s, the sensitivity to horizontal accelerations is better than 3^-6 m s^-2. Effects which limit this sensitivity are discussed.