Source-linked AI summary
Structured optical receivers to attain superadditive capacity and the Holevo limit
Saikat Guha
TL;DR
The Holevo limit generally requires joint measurements over long codeword blocks, while practical structured receiver designs remained an open question. This paper gives a unitary-plus-separable-measurement construction for pure-state channels and concrete BPSK optical examples, including superadditive capacity.
Problem
The Holevo limit generally requires joint measurements over long codeword blocks, and practical structured modulation, coding, and receiver designs remained unresolved.
Source: p. 1Method
For pure-state channels, the paper constructs a projective measurement implemented by a unitary codeword transformation followed by separable single-symbol measurements.
Source: p. 2Results
The construction can attain C∞ for pure-state channels, and a two-symbol BPSK receiver achieves I2/C1 ≈1.0249.
Source: pp. 2–3Takeaways & Limitations
The paper presents structured optical receiver and code examples for superadditive capacity with low-photon BPSK that can be tested using laboratory optics.
Source: p. 1The results assume a purity-preserving channel whose only noise is physical detection; practical code design for approaching the Holevo capacity remains open.
Source: pp. 1, 4
Abstract
from arXiv · showhide
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.