Gaussian quantum discord

TL;DR

This paper extends quantum discord to continuous variable systems, specifically Gaussian states, and analyzes how it varies with state parameters and noise, revealing its relation to entanglement.

Contribution

It introduces a method to compute Gaussian quantum discord for bipartite Gaussian states and explores its behavior in different states and noisy environments.

Findings

Almost all squeezed thermal states have nonzero Gaussian discord.

Discord distinguishes between separable and entangled states based on a threshold.

Gaussian measurements minimize the discord compared to projective measurements.

Abstract

We extend the quantum discord to continuous variable systems and evaluate Gaussian quantum discord C(\rho) for bipartite Gaussian states. In particular, for squeezed thermal states (STS), we explicitly maximize the extractable information over Gaussian measurements: C(\rho) is minimized by a generalized measurement rather than a projective one. Almost all STS have nonzero Gaussian discord: they may be either separable or entangled if the discord is below the threshold C(\rho)=1, whereas they are all entangled above the threshold. We elucidate the general role of state parameters in determining the discord and discuss its evolution in noisy channels.