Quantum Correlations beyond Entanglement and Discord

TL;DR

This paper experimentally demonstrates a form of quantum correlation that exists without entanglement or discord, using Glauber-Sudarshan functions, and explores its robustness and potential for quantum information applications.

Contribution

It introduces and experimentally realizes a new type of quantum correlation beyond entanglement and discord, showing its robustness and potential for activation in quantum information.

Findings

Quantum correlations exist without entanglement or discord.

The correlations are certified via negativities in the Glauber-Sudarshan function.

The state is robust against dephasing, requiring fewer resources.

Abstract

Dissimilar notions of quantum correlations have been established, each being motivated through particular applications in quantum information science and each competing for being recognized as the most relevant measure of quantumness. In this contribution, we experimentally realize a form of quantum correlation that exists even in the absence of entanglement and discord. We certify the presence of such quantum correlations via negativities in the regularized two-mode Glauber-Sudarshan function. Our data show compatibility with an incoherent mixture of orthonormal photon-number states, ruling out quantum coherence and other kinds of quantum resources. By construction, the quantumness of our state is robust against dephasing, thus requiring fewer experimental resources to ensure stability. In addition, we theoretically show how multimode entanglement can be activated based on the generated, nonentangled state. Therefore, we implement a robust kind of nonclassical photon-photon correlated state with useful applications in quantum information processing.