Back action in quantum electro-optic sampling of electromagnetic vacuum fluctuations

TL;DR

This paper investigates the impact of measurement back action on quantum electro-optic sampling of electromagnetic vacuum fluctuations, identifying conditions where back action significantly affects measurements and when it can be neglected.

Contribution

It provides a theoretical analysis of back action effects in electro-optic sampling, including realistic setups with one or two probe beams, and determines regimes where back action contaminates the measurements.

Findings

Back action can significantly contaminate noise profiles at certain parameters.

Shot noise in different probe channels remains uncorrelated due to vacuum fluctuations.

A regime exists where electro-optic sampling effectively measures quantum fields without back-action interference.

Abstract

The influence of measurement back action on electro-optic sampling of electromagnetic quantum fluctuations is investigated. Based on a cascaded treatment of the nonlinear interaction between a near-infrared coherent probe and the mid-infrared vacuum, we account for the generated electric-field contributions that lead to detectable back action. Specifically, we theoretically address two realistic setups, exploiting one or two probe beams for the nonlinear interaction with the quantum vacuum, respectively. The setup parameters at which back action starts to considerably contaminate the measured noise profiles are determined. Due to the vacuum fluctuations entering at the beam splitter, the shot noise of two incoming probe pulses in different channels is uncorrelated. This leads to the absence of the base-level shot noise in the correlation, while further contributions due to nonlinear shot-noise enhancement are still present. Ultimately, the regime in which electro-optic sampling of quantum fields can be considered as effectively back-action free is found.