Testing Quantum Devices: Practical Entanglement Verification in Bipartite Optical Systems

TL;DR

This paper introduces a practical method for verifying entanglement in bipartite optical quantum systems, reducing resource requirements and highlighting security considerations in quantum key distribution.

Contribution

It formulates necessary separability criteria using expectation values and partial transposition, and demonstrates a protocol based on coherent states and homodyne detection for entanglement verification.

Findings

Effective entanglement verification reduces resource use.

A protocol using coherent states and homodyne detection is proposed.

Identifies a security threat in quantum key distribution involving phase references.

Abstract

We present a method to test quantum behavior of quantum information processing devices, such as quantum memories, teleportation devices, channels and quantum key distribution protocols. The test of quantum behavior can be phrased as the verification of effective entanglement. Necessary separability criteria are formulated in terms of a matrix of expectation values in conjunction with the partial transposition map. Our method is designed to reduce the resources for entanglement verification. A particular protocol based on coherent states and homodyne detection is used to illustrate the method. A possible test for the quantum nature of memories using two non-orthogonal signal states arises naturally. Furthermore, closer inspection of the measurement process in terms of the Stokes operators reveals a security threat for quantum key distribution involving phase reference beams.