Photon number statistics uncover the fluctuations in non-equilibrium lattice dynamics

TL;DR

This paper demonstrates a method to measure atomic position fluctuations in non-equilibrium solids by mapping them onto photon number fluctuations in scattered light, revealing quantum phonon squeezing.

Contribution

It introduces a quantum optical approach to directly link atomic displacement variance with measurable photon number fluctuations in non-equilibrium lattice dynamics.

Findings

Photon number fluctuations reflect atomic position variances.

Quantum squeezing of thermal phonons is observed in $$-quartz.

Method bridges atomic fluctuations and optical measurements.

Abstract

Fluctuations of the atomic positions are at the core of a large class of unusual material properties ranging from quantum para-electricity to high temperature superconductivity. Their measurement in solids is the subject of an intense scientific debate focused on seeking a methodology capable of establishing a direct link between the variance of the atomic displacements and experimentally measurable observables. Here we address this issue by means of non-equilibrium optical experiments performed in shot-noise limited regime. The variance of the time dependent atomic positions and momenta is directly mapped into the quantum fluctuations of the photon number of the scattered probing light. A fully quantum description of the non-linear interaction between photonic and phononic fields is benchmarked by unveiling the squeezing of thermal phonons in $\alpha$-quartz.