Ultrafast pump-probe phase-randomized tomography

TL;DR

This paper introduces ultrafast phase randomized tomography, combining pump-probe experiments with quantum optical state tomography to measure non-equilibrium dynamics in materials with high temporal resolution.

Contribution

It presents a novel time-resolved multimode heterodyne detection scheme using phase-randomized ultrashort laser pulses, overcoming phase stability issues for reconstructing optical observables.

Findings

Validated by measuring coherent phonon response in α-quartz

Set an upper limit to non-classical features of phononic states

Enabled access to nonequilibrium quantum fluctuations in complex materials

Abstract

Measuring fluctuations in matter's low energy excitations is the key to unveil the nature of the nonequilibrium response of materials. A promising outlook in this respect is offered by spectroscopic methods that address matter fluctuations by exploiting the statistical nature of light-matter interactions with weak few-photon probes. Here we report the first implementation of ultrafast phase randomized tomography, combining pump-probe experiments with quantum optical state tomography, to measure the ultrafast non-equilibrium dynamics in complex materials. Our approach utilizes a time-resolved multimode heterodyne detection scheme with phase-randomized coherent ultrashort laser pulses, overcoming the limitations of phase-stable configurations and enabling a robust reconstruction of the statistical distribution of phase-averaged optical observables. This methodology is validated by measuring the coherent phonon response in $\alpha$-quartz. By tracking the dynamics of the shot-noise limited photon number distribution of few-photon probes with ultrafast resolution, our results set an upper limit to the non-classical features of phononic state in $\alpha$-quartz and provide a pathway to access nonequilibrium quantum fluctuations in more complex quantum materials.