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Quantum Information and Measurement (QIM)

Entanglement-Assisted Communication Surpassing the Ultimate Classical Capacity

Shuhong Hao, Haowei Shi, Wei Li, Jeffrey H. Shapiro, Quntao Zhuang, Zheshen Zhang

Published Jan 1, 2021• 7 citations
Publisher

Abstract

We report experimental entanglement-assisted communication above the ultimate classical capacity set by the Holevo-Schumacher-Westmorel bound. A high-efficiency entanglement source and a phase-conjugate quantum receiver reap the benefit of pre-shared entanglement over lossy and noisy channels.
DOI
10.1364/qim.2021.tu3b.4

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Entanglement assisted (EA) communication represents an interesting alternative to classical communication, in particular in low-brightness and highly noisy regime when it outperforms significantly corresponding classical counterpart in terms of the channel capacity. Even though that the EA capacity is known for decades the optimum quantum receiver has not been determined yet. In this paper, we propose several low-complexity quantum receivers outperforming recently proposed receivers employing the optical parametric amplifier as a basic building block. We demonstrate by simulations that the capacity of the proposed EA schemes, employing Gaussian modulation and the proposed low-complexity joint receivers, can significantly outperform both the Holevo capacity and classical homodyne and heterodyne channel capacities.
Entanglement offers substantial advantages in quantum information processing, but loss and noise hinder its application in practical scenarios. Although it has been well known for decades that the classical communication capacity of lossy and noisy bosonic channels can be significantly enhanced by entanglement, no practical encoding and decoding schemes are available to realize any entanglement-enabled advantage. Here, we report structured encoding and decoding schemes for such an entanglement-assisted communication scenario. Specifically, we show that phase encoding on an entangled two-mode squeezed vacuum state saturates the entanglement-assisted classical communication capacity of a very noisy channel and overcomes the fundamental limit on covert communication that exists without the assistance of entanglement. We then construct receivers for optimum hypothesis-testing protocols with discrete phase modulation and for optimum noisy phase-estimation protocols with continuous phase modulation. Our results pave the way for entanglement-assisted communication and sensing in the radio-frequency and microwave spectral ranges.