Thermometric machine for ultraprecise thermometry of low temperatures

TL;DR

This paper introduces a novel quantum thermometry scheme using a non-thermalizing two-level probe coupled to an auxiliary hot bath, enabling ultraprecise temperature measurements at very low temperatures.

Contribution

A new thermometric method that avoids thermalization, allowing high-precision low-temperature measurements with fewer resources.

Findings

Probe reaches a steady state with high signal-to-noise ratio proportional to 1/T

Significant reduction in the number of measurements needed for a given precision

Numerical simulations confirm the efficiency of the proposed scheme

Abstract

Thermal equilibrium states are exponentially hard to distinguish at very low temperatures, making equilibrium quantum thermometry in this regime a formidable task. We present a thermometric scheme that circumvents this limitation, by using a two-level probe that does not thermalize with the sample whose temperature is measured. This is made possible thanks to a suitable interaction that couples the probe to the sample and to an auxiliary thermal bath known to be at a higher temperature. Provided a reasonable upper bound on the temperature of the sample, the resulting 'thermometric machine' drives the probe towards a steady state whose signal-to-noise ratio can achieve values as high as $\mathcal{O}(1/T)$. We also characterize the transient state of the probe and numerically illustrate an extreme reduction in the number of measurements to attain a given precision, as compared to optimal measurements on a thermalized probe.