Phase-locked amplification enhanced by spin squeezing

TL;DR

This paper proposes a novel detection scheme combining phase-locked amplification with spin squeezing in atomic ensembles to enhance phase sensitivity and extend the detection range for magnetic field sensing.

Contribution

It introduces a method to integrate quadrature spin squeezing with phase locking, improving sensitivity and detection window in quantum magnetic field measurements.

Findings

Enhanced phase sensitivity through combined squeezing and locking.

Extended detection window beyond the uncertainty limit.

Optimal pulse schemes for concurrent squeezing and phase locking.

Abstract

Quantum lock-in amplification raises the detection sensitivity of magnetic fields to unprecedented levels by phase-locked pumping the Zeeman levels of a single trapped atom. However, random spin precessions limits the useful detection range of arming times for locking high-contrast signals. To extend this range imposed by the uncertainty limit, quadrature spin squeezing can be introduced, on top of the phase-locking mechanism. We propose a detection scheme using an atomic ensemble whose collected spin is pumped by two lasers for simultaneous squeezing and phase locking. We derive the optimal $\pi/2$-pulse and $\pi$-pulse schemes that accomplishes this concurrent action and prove that the resulting phase sensitivity is enhanced while the usable detection window for phase locking is widened.