Abstract
Entanglement offers substantial advantages in quantum information processing, but loss and noise hinder its applications in practical scenarios. Although it has been well known for decades that the classical communication capacity over 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 the entangled two-mode squeezed vacuum state saturates the entanglement-assisted classical communication capacity over a very noisy channel and overcomes the fundamental limit of covert communication without entanglement assistance. We then construct receivers for optimum hypothesis testing protocols under discrete phase modulation and for optimum noisy phase estimation protocols under continuous phase modulation. Our results pave the way for entanglement-assisted communication and sensing in the radio-frequency and microwave spectral ranges.
Highlights
The benefit of entanglement for quantum information processing has been revealed by pioneering work in communication [1], sensing [2,3,4], and computation [5]
Compared with the classical capacity without entanglement assistance, i.e., the HolevoSchumacher-Westmoreland capacity, C ( ) [18,19,20], the improvement enabled by entanglement can be drastic even over a noisy channel
After transducing the signal received from Bob, Alice jointly measures the signal mode and the entangled idler mode retrieved from another quantum memory to decode the classical information
Summary
The benefit of entanglement for quantum information processing has been revealed by pioneering work in communication [1], sensing [2,3,4], and computation [5]. The advantage enabled by the initial entanglement even survives loss and noise in certain entanglementbreaking scenarios, as predicted [6,7,8,9] and experimentally demonstrated [10,11,12], in the entanglement-enhanced sensing protocol called quantum illumination. It is known, in theory, that preshared entanglement increases the classical communication capacity, i.e., the maximum rate of reliable communication of classical bits (cbits), of a quantum channel (a completely positive trace-preserving map).
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