Accurate trajectory alignment in cold-atom interferometers with separated laser beams

TL;DR

This paper introduces a precise alignment method for separated laser beams in cold-atom interferometers, significantly reducing systematic errors and improving the accuracy of inertial sensors and gravitational wave detectors.

Contribution

It presents a novel alignment technique achieving 0.2 μrad precision and a method to determine atomic wave packet velocity with 0.2 mm/s accuracy, enhancing interferometer stability.

Findings

Laser beam alignment at 0.2 μrad level

Atomic wave packet velocity determined with 0.2 mm/s accuracy

Gyroscope bias constrained to 1×10⁻¹⁰ rad·s⁻¹

Abstract

Cold-atom interferometers commonly face systematic effects originating from the coupling between the trajectory of the atomic wave packet and the wave front of the laser beams driving the interferometer. Detrimental for the accuracy and the stability of such inertial sensors, these systematics are particularly enhanced in architectures based on spatially separated laser beams. Here we analyze the effect of a coupling between the relative alignment of two separated laser beams and the trajectory of the atomic wave packet in a four-light-pulse cold-atom gyroscope operated in fountain configuration. We present a method to align the two laser beams at the $0.2 \ \mu$rad level and to determine the optimal mean velocity of the atomic wave packet with an accuracy of $0.2\ \textrm{mm}\cdot\textrm{s}^{-1}$. Such fine tuning constrains the associated gyroscope bias to a level of $1\times 10^{-10}~\textrm{rad}\cdot\textrm{s}^{-1}$. In addition, we reveal this coupling using the point-source interferometry technique by analyzing single-shot time-of-flight fluorescence traces, which allows us to measure large angular misalignments between the interrogation beams. The alignment method which we present here can be employed in other sensor configurations and is particularly relevant to emerging gravitational wave detector concepts based on cold-atom interferometry.