Quantum mutual information of an entangled state propagating through a fast-light medium

TL;DR

This paper investigates how quantum correlations and mutual information propagate through fast-light media, revealing that quantum correlations can be slightly advanced while entanglement persists, but mutual information's leading edge is not advanced due to noise.

Contribution

It provides the first detailed study of quantum mutual information propagation in fast-light media, showing partial advancement of correlations and the effects of noise on information edges.

Findings

Quantum correlations can be advanced by a small fraction of the correlation time.

Entanglement is preserved despite noise from phase-insensitive gain.

Mutual information's leading edge is not advanced due to noise degradation.

Abstract

Although it is widely accepted that classical information cannot travel faster than the speed of light in vacuum, the behavior of quantum correlations and quantum information propagating through actively-pumped fast-light media has not been studied in detail. To investigate this behavior, we send one half of an entangled state of light through a gain-assisted fast-light medium and detect the remaining quantum correlations. We show that the quantum correlations can be advanced by a small fraction of the correlation time while the entanglement is preserved even in the presence of noise added by phase-insensitive gain. Additionally, although we observe an advance of the peak of the quantum mutual information between the modes, we find that the degradation of the mutual information due to the added noise appears to prevent an advancement of the leading edge. In contrast, we show that both the leading and trailing edges of the mutual information in a slow-light system can be significantly delayed.