Compression of Entanglement Improves Quantum Communication

TL;DR

This paper demonstrates that compressing high-dimensional entanglement into lower dimensions can outperform coherence-preserving protocols in quantum communication, highlighting the importance of non-unitary operations.

Contribution

It introduces a novel quantum communication protocol utilizing entanglement compression, surpassing traditional coherence-preserving methods, with experimental validation using a single photon setup.

Findings

High-dimensional entanglement can be compressed into qubits for improved communication.

Non-unitary encoding operations can outperform unitary, coherence-preserving protocols.

Experimental realization achieves near-optimal fidelity in entanglement compression.

Abstract

Shared entanglement can significantly amplify classical correlations between systems interacting over a limited quantum channel. A natural avenue is to use entanglement of the same dimension as the channel because this allows for unitary encodings, which preserve global coherence until a measurement is performed. Contrasting this, we here demonstrate a distributed task based on a qubit channel, for which irreversible encoding operations can outperform any possible coherence-preserving protocol. This corresponds to using high-dimensional entanglement and encoding information by compressing one of the subsystems into a qubit. Demonstrating this phenomenon requires the preparation of a four-dimensional maximally entangled state, the compression of two qubits into one and joint qubit-ququart entangled measurements, with all modules executed at near-optimal fidelity. We report on a proof-of-principle experiment that achieves the advantage by realizing separate systems in distinct and independently controlled paths of a single photon. Our result demonstrates the relevance of high-dimensional entanglement and non-unitary operations for enhancing the communication capabilities of standard qubit transmissions.