Speaker
Description
Atom interferometers are reaching sensitivities fundamentally constrained by quantum fluctuations [1]. A main challenge is to integrate entanglement into quantum sensing protocols to enhance precision while ensuring robustness against noise and systematics [2-4]. Here, we theoretically investigate differential phase measurements with two atom interferometers using spin-squeezed states [5], accounting for common-mode phase noise spanning the full $2\pi$ range. We estimate the differential signal using model-free ellipse fitting [6], a robust method requiring no device calibration and resilient to additional noise sources. Our results show that spin-squeezing enables sensitivities below the standard quantum limit (SQL). Specifically, we identify optimal squeezed states that minimize the differential phase uncertainty, scaling as $N^{-2/3}$, thus overcoming the SQL, while eliminating the bias inherent in ellipse fitting methods. We benchmark our protocol against the Cramér-Rao bound and compare it with hybrid methods that incorporate auxiliary classical sensors. Our findings provide a pathway to robust and high-precision atom interferometry, in realistic noisy environments and using readily available states and estimation methods.
[1] L. Pezzè, A. Smerzi, M. K. Oberthaler, R. Schmied, and P. Treutlein,
Quantum metrology with nonclassical states of atomic ensembles, Rev. Mod. Phys. 90, 035005 (2018)
[2] A. Andrè, A. S. Sorensen, and M. D. Lukin,
Stability of Atomic Clocks Based on Entangled Atoms, Phys. Rev. Lett. 92, 230801 (2004).
[3] B. Braverman, A. Kawasaki, and V. Vuletić, Impact of non-unitary spin squeezing on atomic clock performance, New. J. Phys. 20, 103019 (2018)
[4] L. Pezzè and A. Smerzi,
Heisenberg-Limited Noisy Atomic Clock Using a Hybrid Coherent and Squeezed State Protocol, Phys. Rev. Lett. 125, 210503 (2020).
[5] M. Kitagawa and M. Ueda, Squeezed spin states, Phys. Rev. A 47, 5138 (1993)
[6] G. T. Foster, J. B. Fixler, J. M. McGuirk, and M. A. Kasevich, Method of phase extraction between coupled atom interferometers using ellipse-specific fitting, Opt. Lett. 27, 951 (2002).
