Coherent spin control by electromagnetic vacuum fluctuations

TL;DR

This paper demonstrates a novel method of controlling spin coherence using electromagnetic vacuum fluctuations, exploiting pathway correlations in a three-level system to achieve optical spin echo without traditional stimulated Raman processes.

Contribution

It introduces a new class of optical nonlinearity driven by vacuum fluctuations, enabling all-optical spin control through pathway correlation effects.

Findings

Demonstration of spin-flip control via vacuum fluctuation correlations

Observation of all-optical spin echo in nonlinear optics

Reduction of optical field requirements compared to stimulated Raman processes

Abstract

In coherent control, electromagnetic vacuum fluctuations usually cause coherence loss through irreversible spontaneous emission. However, since the dissipation via emission is essentially due to correlation of the fluctuations, when emission ends in a superposition of multiple final states, correlation between different pathways may build up if the "which-way" information is not fully resolved (i.e., the emission spectrum is broader than the transition energy range). Such correlation can be exploited for spin-flip control in a $\Lambda$-type three-level system, which manifests itself as an all-optical spin echo in nonlinear optics with two orders of optical fields saved as compared with stimulated Raman processes. This finding represents a new class of optical nonlinearity induced by electromagnetic vacuum fluctuations.