Enhanced squeezing for quantum gravimetry in a Bose-Einstein condensate with focussing

TL;DR

This paper enhances quantum gravimetry using Bose-Einstein condensates by applying a delta kick to increase density and spin squeezing, achieving a fourfold sensitivity improvement over previous methods.

Contribution

It introduces a novel state preparation technique with a delta kick to improve spin squeezing in quantum gravimetry.

Findings

Phase sensitivity surpasses the standard quantum limit by a factor of ~20.

Fourfold improvement over the original scheme without the delta kick.

Performance well captured by a two-mode approximation.

Abstract

Free-fall atom interferometers offer a powerful platform for accurate, absolute gravitational sensing. Szigeti et al. [Phys. Rev. Lett. 125, 100402 (2020)] recently proposed a quantum-enhanced scheme that uses a spin-squeezed Bose-Einstein condensate as an input state to improve the phase sensitivity of the interferometer. The spin squeezing, generated via one-axis twisting interactions, was limited by condensate expansion. Here we present an improved state preparation in which a sudden trapping potential -- a delta kick -- is initially applied to focus the condensate. The resulting increase in density enhances the one-axis-twisting interactions and produces greater spin squeezing. Using multimode truncated-Wigner simulations, we quantify the performance of the interferometer and find that, for an optimal kick strength, the phase sensitivity surpasses the standard quantum limit by a factor of $\sim 20$. This represents a fourfold improvement over the original scheme without the delta kick and is well captured by a two-mode approximation.