Entanglement verification via nonlinear witnesses

TL;DR

This paper demonstrates that nonlinear entanglement witnesses outperform linear ones in verifying entanglement, especially for mixed states with orbital angular momentum, with potential applications in quantum communication.

Contribution

The work introduces and experimentally validates the superior performance of nonlinear entanglement witnesses over linear ones for mixed states with orbital angular momentum.

Findings

Nonlinear witnesses reliably detect entanglement in mixed OAM states.

Nonlinear witnesses outperform linear witnesses in accuracy.

Method has potential applications in quantum communication protocols.

Abstract

The controlled generation of entangled states and their subsequent detection are integral aspects of quantum information science. In this work, we analyse the application of nonlinear witnesses to the verification of entanglement, and we demonstrate experimentally that nonlinear witnesses perform significantly better than linear witnesses. Specifically, we demonstrate that a single non- linear entanglement witness is able to determine to a high degree of certainty that a mixed state containing orbital angular momentum (OAM) entanglement of specific forms is entangled for any relative phase and sufficient fidelity. This is a significant improvement over linear witnesses, which cannot provide the same level of performance. We envisage that nonlinear witnesses and our method of state preparation will have further uses in areas of quantum science such as superdense coding and quantum key distribution.