Waveguide-QED-based measurement of a reservoir spectral density

TL;DR

This paper introduces a static, universal method to measure the spectral density of a reservoir in open quantum systems using photon scattering, without requiring system excitation or dynamic tracking.

Contribution

It presents a novel approach to determine the spectral density directly from photon reflection and transmission spectra, applicable beyond weak-coupling regimes.

Findings

Spectral density can be inferred from photon spectra.

Method works at zero temperature and under the rotating wave approximation.

Applicable to a broad range of open quantum systems.

Abstract

The spectral density (SD) function has a central role in the study of open quantum systems (OQSs). We discover a method allowing for a "static" measurement of the SD - i.e., it requires neither the OQS to be initially excited nor its time evolution tracked in time - which is not limited to the weak-coupling regime. This is achieved through one-dimensional photon scattering for a zero-temperature reservoir coupled to the OQS via the rotating wave approximation. We find that the SD profile is a universal simple function of the photon's reflectance and transmittance. As such, it can be straightforwardly inferred from photon's reflection and transmission spectra.