Generalising multipartite concentratable entanglement for practical applications: mixed, qudit, and optical states

TL;DR

This paper extends the concentratable entanglement measure and c-SWAP test to mixed, qudit, and optical states, making them more practical for experimental quantum information processing.

Contribution

It generalizes the CE measure and c-SWAP test for mixed, higher-dimensional, and optical states, enhancing their applicability in real-world quantum experiments.

Findings

Derived lower bounds for mixed-state CE

Proposed conjectured upper bounds robust to errors

Validated CE for qudit and optical states

Abstract

The controlled SWAP test for detecting and quantifying entanglement applied to pure qubit states is robust to small errors in the states and efficient for large multi-qubit states (Foulds et al. 2021 Quantum Sci. Technol. 6, 035002 (doi:10.1088/2058-9565/abe458)). We extend this, and the related measure concentratable entanglement (CE), to enable important practical applications in quantum information processing. We investigate the lower bound of concentratable entanglement given in (Beckey et al. 2023 Phys. Rev. A 107, 062425 (doi:10.1103/physreva.107.062425)) and conjecture an upper bound of the mixed-state concentratable entanglement that is robust to c-SWAP test errors. Since experimental states are always slightly mixed, our work makes the c-SWAP test and CE measure suitable for application in experiments to characterize entanglement. We further present the CE of some key higher-dimensional states such as qudit states and entangled optical states to validate the CE as a higher-dimensional measure of entanglement. This article is part of the theme issue 'The quantum theory of light'.