Quantum sensing of temperature close to absolute zero in a Bose-Einstein condensate

TL;DR

This paper presents a theoretical method for highly sensitive quantum temperature sensing near absolute zero in a Bose-Einstein condensate using a single-atom impurity qubit, achieving optimal sensitivity and avoiding divergence issues.

Contribution

It introduces a novel quantum sensing scheme utilizing a single-atom impurity qubit to measure ultra-low temperatures in a BEC with optimal sensitivity and finite bounds.

Findings

Sensitivity saturates the quantum Cramer-Rao bound.

Quantum signal-to-noise ratio reaches a maximum at an optimal encoding time.

Sensing error does not diverge near absolute zero in the weak coupling regime.

Abstract

We propose a theoretical scheme for quantum sensing of temperature close to absolute zero in a quasi-one-dimensional Bose-Einstein condensate (BEC). In our scheme, a single-atom impurity qubit is used as a temper-ature sensor. We investigate the sensitivity of the single-atom sensor in estimating the temperature of the BEC. We demonstrate that the sensitivity of the temperature sensor can saturate the quantum Cramer-Rao bound by means of measuring quantum coherence of the probe qubit. We study the temperature sensing performance by the use of quantum signal-to-noise ratio (QSNR). It is indicated that there is an optimal encoding time that the QSNR can reach its maximum in the full-temperature regime. In particular, we find that the QSNR reaches a finite upper bound in the weak coupling regime even when the temperature is close to absolute zero, which implies that the sensing-error-divergence problem is avoided in our scheme. Our work opens a way for quantum sensing of temperature close to absolute zero in the BEC.