Structured optical receivers to attain superadditive capacity and the Holevo limit

TL;DR

This paper introduces a structured optical receiver design that achieves superadditive capacity and approaches the Holevo limit by performing joint measurements on quantum codewords, surpassing traditional symbol-by-symbol detection methods.

Contribution

The authors present a novel receiver architecture capable of attaining the ultimate quantum channel capacity through joint measurements, demonstrating superadditivity in photon-information-efficient communication.

Findings

Achieves capacity close to the Holevo limit with structured joint-detection receivers.

Demonstrates superadditivity in quantum optical communication channels.

Provides concrete code and receiver designs surpassing conventional detection methods.

Abstract

When classical information is sent over a quantum channel, attaining the ultimate limit to channel capacity requires the receiver to make joint measurements over long codeword blocks. For a pure-state channel, we construct a receiver that can attain the ultimate capacity by applying a single-shot unitary transformation on the received quantum codeword followed by simultaneous (but separable) projective measurements on the single-modulation-symbol state spaces. We study the ultimate limits of photon-information-efficient communications on a lossy bosonic channel. Based on our general results for the pure-state quantum channel, we show some of the first concrete examples of codes and structured joint-detection optical receivers that can achieve fundamentally higher (superadditive) channel capacity than conventional receivers that detect each modulation symbol individually.