We study the statistics of the kinetic (or, equivalently, potential) energy for $N$ noninteracting fermions in a $1d$ harmonic trap of frequency $\omega$ at finite temperature $T$. Remarkably, we find an exact solution for the full distribution of the kinetic energy, at any temperature $T$ and for any $N$, using a nontrivial mapping to an integrable Calogero-Moser-Sutherland model. As a function of temperature $T$ and for large $N$, we identify (i) a quantum regime, for $T\sim \hslash \omega$, where quantum fluctuations dominate and (ii) a thermal regime, for $T\sim N\hslash \omega$, governed by thermal fluctuations. We show how the mean and the variance as well as the large deviation function associated with the distribution of the kinetic energy cross over from the quantum to the thermal regime as $T$ increases.

• Received 6 April 2017

DOI:https://doi.org/10.1103/PhysRevLett.119.130601