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arXiv:2609.00991 · Physical Review A

Impact of light-shift inhomogeneities on the contrast of light-pulse atom interferometers

Anonymous, Diego Alejandro Lancheros Naranjo, Rayan Si-Ahmed, Gabriel Ducasse, Franck Pereira dos Santos, Sébastien Merlet

Published Aug 10, 2026• 0 citations
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Abstract

We study the loss of the contrast in an atom interferometer when increasing the duration of Raman mirror pulses, and find the contrast decay rate to increase with the interferometer duration. We attribute this effect to the transverse spatial fluctuations of the intensity across the Raman beams, and to the dephasing induced by the associated light shifts inhomogeneities. Simulations based on the propagation of noisy synthetic Raman beams show that the contrast decay rate increases with the distance between the wavepackets at the mirror pulse, before reaching an asymptotic limit when intensity fluctuations between the two wavepackets become completely decorrelated. Finally, simulations based on the propagation of Raman beams having their measured intensity fluctuations predict contrast loss rates consistent with our measurements, confirming the detrimental role for the interferometer contrast played by intensity fluctuations across the interferometer laser beams.

DOI
10.1103/hb9l-14x7

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We study the loss of the contrast in an atom interferometer when increasing the duration of Raman mirror pulses, and find the contrast decay rate to increase with the interferometer duration. We attribute this effect to the transverse spatial fluctuations of the intensity across the Raman beams, and to the dephasing induced by the associated light shifts inhomogeneities. Simulations based on the propagation of noisy synthetic Raman beams show that the contrast decay rate increases with the distance between the wavepackets at the mirror pulse, before reaching an asymptotic limit when intensity fluctuations between the two wavepackets become completely decorrelated. Finally, simulations based on the propagation of Raman beams having their measured intensity fluctuations predict contrast loss rates consistent with our measurements, confirming the detrimental role for the interferometer contrast played by intensity fluctuations across the interferometer laser beams.
Atom interferometry relies on the separation and recombination of atom wavepackets. When the two paths overlap perfectly at the end of the interferometer, the phase is insensitive to the atomic velocity distribution. Here, we show that, when the separation and recombination is performed using a Raman transition there is a displacement of the atomic wavepacket due to a phase shift during light pulses. Because of the variation of the laser intensity seen by the atoms, there is an imperfect cancellation of these displacements. The observation of a velocity-dependent phase shift on the interferometer is the signature of this effect, which has been modeled. Thanks to the signature we have identified, we are able to compensate for this effect by applying laser power ramps during the interferometer to mitigate intensity variations.
The use of cold atoms in any sensor operating in a dynamic environment requires that the measurement cycle be conducted before the atom cloud escapes the interaction region. Under multiple-g accelerations it is desirable to complete measurements in millisecond time scales, particularly when laser beams are used to interrogate the atoms. In this paper, we demonstrate high-contrast atom interferometry in a vapor cell using stimulated Raman transitions at millisecond interrogation times. Laser-cooled cesium atoms are interrogated with a sequence of three Raman pulses and the interferometer phase is read out in the same region in which the atoms are trapped. Our system achieved over 70% contrast with a Doppler insensitive interferometer and over 30% contrast with a Doppler sensitive interferometer, in an environment normally considered adverse to high-contrast atom interferometry (e.g., no retroreflector stabilization and no magnetic shielding). Demonstration of an inertially sensitive atom interferometer in this environment supports the feasibility of a high-bandwidth inertial sensor using light pulse atom interferometry. Finally, we show that Raman pulse population transfer efficiency in our system is primarily limited by nonuniformity of the Raman laser intensity across the atom cloud.
Imperfect Raman pulses can lead to the formation of multiple interfering paths and affect the output of an atom interferometer in high-precision measurement.We study the effect of the imperfect Raman pulses on the interferometric fringe contrast and the phase shift in the three-pulse atom interferometer by using the evolution operator method.Analytical expressions expanded to the second-order fluctuation of imperfect pulses are derived, in which the effect of coupling the imperfect pulses with laser detuning and pulse duration is also considered.The result indicates that the second-order fluctuation of imperfect pulses is dominant, however, it can be nearly ignored in the current requirements of atomic experiments.Even so, theoretical analysis is very necessary as it may be helpful in proposing some schemes to improve the interference efficiency for future high-precision measurements with atomic interferometry.
Atom interferometers consist of light pulses designed to create coherent superpositions of atomic states (“π/2” or “beam splitting” pulses) and that coherently interchange states (“π” or “mirror” pulses). In this article, we investigate the effects of imperfect pulses for a geometry specific to our apparatus. Atoms emerge from a 2-dimensional magneto-optical trap (2D MOT) in a continuous beam and cross continuous laser beams that drive stimulated Raman transitions. We use the atoms’ transit time through the laser field as the “pulse” time. We describe the impact of various effects on the contrast of the Rabi cycling, specifically the longitudinal velocity spread, the laser beam diameter and the spacing between the laser beams.
The mirrors and beamsplitters of atom interferometers often suffer from inhomogeneities in coupling strength and effective detuning because different atoms see different laser intensities, Zeeman and Doppler shifts and are in different Zeeman sub-states. This limits the fringe visibility for a simple interferometer, which falls off rapidly if extra mirrors are added, for example to increase the interferometer area. In practice, one usually therefore filters the atomic velocities/sub-states, thus losing signal, and/or restricting operation to small-area interferometers with low sensitivity. The problem is familiar in the field of NMR, where, instead of using simple pi or pi/2 pulses, the phase and potentially amplitude are modulated during the pulse so as to make the result robust to the inhomogeneities encountered. Despite the similarities with NMR systems, the numbers, correlations and performance measures for atom interferometry are different. We have used optimal control theory to obtain robust high fidelity mirror pulses for atom interferometry. Importantly, while the designs are found by computational simulation, we can validate them experimentally, with remarkably good agreement. We have addressed the optimization of individual mirror pulses, but the eventual aim is to optimize the interferometer as a whole: errors introduced in one pulse can be compensated at a later stage, for example. Our pulses yield high contrast without the need to filter the atomic sample and maintain this even in the case of extended pulse sequences, thus making it possible to achieve significantly larger interferometer areas than with simple pi pulses.
Correlations between the internal and external degrees of freedom of neutral atoms enable state-of-the-art accuracy and sensitivity in inertial sensors. This thesis presents the latest developments in the absolute cold-atom gravimeter (CAG) of the LTE, based on momentum-state interferometry using Raman transitions in a freely falling atomic cloud of 87 Rb. We identify intensity inhomogeneities as a primary source of contrast loss in the CAG and highlight the role of non-resonant interactions resulting from the counter propagating geometry of the Raman beams. Following optimization of the optical setup, the interferometer contrast improved by nearly 10%, with local intensity-related features successfully eliminated. Additionally, we identified bias phases arising from intensity variations, predominantly during the mirror pulse. We introduce a dynamical method for evaluating these phase shifts, which generalizes the traditional adiabatic approximation. This method enables us to distinguish between phase shifts caused by two-photon processes and those of other origins. Crucially, it links the population of stray momentum states to the accumulation of nonlinear phase shifts at the interferometers output ports. We report a systematic bias in the measurement of g at the level of 5 × 10−9 g, attributed to intensity inhomogeneities, and a sensitivity of 20 × 10−9 g Hz−1/2.