Compression of Entanglement Improves Quantum Communication

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.

7 pages, 5 figures + appendix. Comments are welcome. V2: expanded and reformatted theory section, added experimental details. V3: updated to match journal version

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Cited by in corpus (3)

• Information capacity of quantum communication under natural physical assumptions
• The role of entanglement in energy-restricted communication and randomness generation
• Quantum inputs in the prepare-and-measure scenario and stochastic teleportation