Bending the rules of low-temperature thermometry with periodic driving

TL;DR

This paper demonstrates that periodic driving of a probe can significantly enhance low-temperature thermometry precision, overcoming fundamental limits and enabling sub-nanokelvin sensitivity improvements in quantum systems.

Contribution

It introduces an exact solution for a periodically driven probe in equilibrium samples, showing how near-resonant modulation improves thermometric sensitivity at very low temperatures.

Findings

Weak near-resonant modulation enhances signal-to-noise ratio.

Periodic driving changes the thermal sensitivity power law.

Sensitivity improved by orders of magnitude in impurity thermometry.

Abstract

There exist severe limitations on the accuracy of low-temperature thermometry, which poses a major challenge for future quantum-technological applications. Low-temperature sensitivity might be manipulated by tailoring the interactions between probe and sample. Unfortunately, the tunability of these interactions is usually very restricted. Here, we focus on a more practical solution to boost thermometric precision -- driving the probe. Specifically, we solve for the limit cycle of a periodically modulated linear probe in an equilibrium sample. We treat the probe-sample interactions \textit{exactly} and hence, our results are valid for arbitrarily low temperatures $ T $ and any spectral density. We find that weak near-resonant modulation strongly enhances the signal-to-noise ratio of low-temperature measurements, while causing minimal back action on the sample. Furthermore, we show that near-resonant driving changes the power law that governs thermal sensitivity over a broad range of temperatures, thus `bending' the fundamental precision limits and enabling more sensitive low-temperature thermometry. We then focus on a concrete example -- impurity thermometry in an atomic condensate. We demonstrate that periodic driving allows for a sensitivity improvement of several orders of magnitude in sub-nanokelvin temperature estimates drawn from the density profile of the impurity atoms. We thus provide a feasible upgrade that can be easily integrated into low-$T$ thermometry experiments.