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arXiv:2502.03334 · Physical Review Research

Large momentum transfer Raman atom interferometer without k -reversal

Guanchen Peng, Bryony Lanigan, Robert Shah, Jongseok Lim, Aisha Kaushik, Joseph P. Cotter, Edward A. Hinds, B. E. Sauer

Published Jul 21, 2025• 2 citations
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Abstract

We present a Raman atom interferometer using large momentum transfer without reversing the direction of the effective wave vector ( k -reversal). More specifically, we use a microwave π / 2 pulse to manipulate the spin state of Rb 87 atoms before applying a Raman light π pulse to achieve 4 ℏ k momentum transfer per Raman light pulse. A microwave π pulse in the middle of the interferometer sequence reverses the spin states, which allows closing of the interferometer arms by the same Raman light π pulses without propagation reversal. We present a proof-of-principle demonstration of a 4 ℏ k large-momentum-transfer (LMT) atom interferometer and discuss its scalability. Our results extend the scope of using LMT atom optics.

DOI
10.1103/ghlb-v3jc

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We present a Raman atom interferometer using large momentum transfer without reversing the direction of the effective wave vector ( k -reversal). More specifically, we use a microwave π / 2 pulse to manipulate the spin state of Rb 87 atoms before applying a Raman light π pulse to achieve 4 ℏ k momentum transfer per Raman light pulse. A microwave π pulse in the middle of the interferometer sequence reverses the spin states, which allows closing of the interferometer arms by the same Raman light π pulses without propagation reversal. We present a proof-of-principle demonstration of a 4 ℏ k large-momentum-transfer (LMT) atom interferometer and discuss its scalability. Our results extend the scope of using LMT atom optics.
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Large momentum transfer (LMT) is an important technique for magnifying the phase shift accumulated in an atom interferometer. Existing approaches to implement Raman-transition-based LMT all involve physically swapping the propagation directions of the two counterpropagating Raman beams repeatedly, which could significantly complicate the experimental system. Here, we demonstrate a simpler approach for Raman-transition-based LMT that does not involve a physical swap of the directions of the Raman beams. In this approach, both Raman beams are retroreflected, and a Doppler shift induced by a bias velocity of the atoms is used to separate the transition frequencies of the two pairs of counterpropagating Raman beams. Therefore, an effective swap of the directions of the Raman beams can be achieved by shifting the relative frequency between the two Raman beams from the resonant frequency of one pair of the Raman beams to that of the other pair. We demonstrate the use of this technique for LMT-augmented accelerometry using atoms released from a magneto-optic trap.
We report a demonstration of composite Raman pulses that achieve broadband population inversion and are used to increase the momentum splitting of an atom interferometer up to 18ℏk (corresponding to an increase in the inertial signal by a factor of nine). Composite Raman pulses suppress the effects of pulse length and detuning errors, providing higher transfer efficiency and velocity acceptance than single square pulses. We implement two composite pulse sequences, π/20°−π90°−π/20° and π/20°−π180°−3π/20°, and use the latter composite pulse to demonstrate large-area atom interferometry with stimulated Raman transitions. In addition to enabling larger momentum transfer and higher sensitivity, we argue that composite pulses can improve the robustness of atom interferometers operating in dynamic environments.
A point source interferometer (PSI) is a device where atoms are split and recombined by applying a temporal sequence of Raman pulses during the expansion of a cloud of cold atoms behaving approximately as a point source. The PSI can work as a sensitive multi-axes gyroscope that can automatically filter out the signal from accelerations. The phase shift arising from the rotations is proportional to the momentum transferred to each atom from the Raman pulses. Therefore, by increasing the momentum transfer, it should be possible to enhance the sensitivity of the PSI. Here, we investigate the degree of enhancement in sensitivity that could be achieved by augmenting the PSI with large momentum transfer (LMT) employing a sequence of many Raman pulses with alternating directions. We analyze how factors such as Doppler detuning, spontaneous emission, and the finite initial size of the atomic cloud compromise the advantage of LMT and how to find the optimal momentum transfer under these limitations, with both the semi-classical model and a model under which the motion of the center of mass of each atom is described quantum mechanically. We identify a set of realistic parameters for which LMT can improve the PSI by a factor of nearly 40.
Large-momentum-transfer (LMT) atom interferometers using elastic Bragg scattering on light waves are among the most precise quantum sensors to date. To advance their accuracy from the mrad to the μrad regime, it is necessary to understand the rich phenomenology of the Bragg interferometer, which differs significantly from that of a standard two-mode interferometer. We develop an analytic model for the interferometer signal and demonstrate its accuracy using comprehensive numerical simulations. Our analytic treatment allows the determination of the atomic projection noise limit of a LMT Bragg interferometer and provides the means to saturate this limit. It affords accurate knowledge of the systematic phase errors as well as their suppression by 2 orders of magnitude down to a few μrad using appropriate light-pulse parameters.
We present mirror and beamsplitter pulse designs that improve the fidelity of atom interferometry and increase its tolerance of systematic inhomogeneities. These designs are demonstrated experimentally with a cold thermal sample of 85^{85}85Rb atoms. We first show a stimulated Raman inversion pulse design that achieves a ground hyperfine state transfer efficiency of 99.8(3)%, compared with a conventional πππ pulse efficiency of 75(3)%. This inversion pulse is robust to variations in laser intensity and detuning, maintaining a transfer efficiency of 90% at detunings for which the πππ pulse fidelity is below 20%, and is thus suitable for large momentum transfer interferometers using thermal atoms or operating in non-ideal environments. We then extend our optimization to all components of a Mach-Zehnder atom interferometer sequence and show that with a highly inhomogeneous atomic sample the fringe visibility is increased threefold over that using conventional πππ and π/2π/2π/2 pulses.