Quantum discord as a resource for quantum cryptography

TL;DR

Quantum discord serves as a fundamental resource enabling secure quantum key distribution, especially in noisy, device-dependent, and device-independent cryptographic scenarios where entanglement may be compromised.

Contribution

This paper highlights the critical role of quantum discord as a resource for quantum cryptography, extending understanding beyond entanglement in noisy environments.

Findings

Quantum discord is necessary for secure key distribution in noisy settings.

Entanglement is reaffirmed as essential in device-independent cryptography.

Quantum discord can enable cryptography when entanglement is inaccessible.

Abstract

Quantum discord is the minimal bipartite resource which is needed for a secure quantum key distribution, being a cryptographic primitive equivalent to non-orthogonality. Its role becomes crucial in device-dependent quantum cryptography, where the presence of preparation and detection noise (inaccessible to all parties) may be so strong to prevent the distribution and distillation of entanglement. The necessity of entanglement is re-affirmed in the stronger scenario of device-independent quantum cryptography, where all sources of noise are ascribed to the eavesdropper.