Low-temperature thermometry enhanced by strong coupling

Luis A. Correa, Martí Perarnau-Llobet, Karen V. Hovhannisyan, Senaida Hernández-Santana, Mohammad Mehboudi, Anna Sanpera

Published 2016-11-30Version 1

We consider the problem of estimating the temperature $ T $ of a very cold equilibrium sample with an individual quantum probe. In particular, $ T $ is inferred from measurements performed on a single quantum harmonic probe strongly coupled to the sample under investigation. Due to the non-perturbative probe-sample interaction the stationary state of the former will not be thermal, in general. This turns out to be potentially advantageous for measuring low temperatures, as we show that: (i) The thermometric precision at low $ T $ can be significantly enhanced by strengthening the probe-sampling coupling, (ii) the variance of a suitable quadrature of our single-mode thermometer can yield temperature estimates with nearly minimal statistical uncertainty, and (iii) the spectral density of the probe-sample coupling may be engineered to further improve thermometric performance. These observations may find applications in practical nanoscale thermometry at low temperatures---a regime which is particularly relevant to quantum technologies.