Explicit capacity-achieving receivers for optical communication and quantum reading

TL;DR

This paper presents explicit, structured optical receivers that achieve the Holevo limit in optical communication and quantum reading by using a sequential decoding approach with non-destructive measurements and phase-space manipulations.

Contribution

It introduces a practical sequential decoding scheme that achieves the Holevo limit for optical communication and quantum reading, utilizing non-destructive vacuum-or-not measurements and phase-space operations.

Findings

Achieves the Holevo limit using explicit structured receivers.

Introduces a non-destructive vacuum-or-not measurement technique.

Demonstrates practical implementation with phase-space displacements, phase-shifting, and squeezing.

Abstract

An important practical open question has been to design explicit, structured optical receivers that achieve the Holevo limit in the contexts of optical communication and "quantum reading." The Holevo limit is an achievable rate that is higher than the Shannon limit of any known optical receiver. We demonstrate how a sequential decoding approach can achieve the Holevo limit for both of these settings. A crucial part of our scheme for both settings is a non-destructive "vacuum-or-not" measurement that projects an n-symbol modulated codeword onto the n-fold vacuum state or its orthogonal complement, such that the post-measurement state is either the n-fold vacuum or has the vacuum removed from the support of the n symbols' joint quantum state. The sequential decoder for optical communication requires the additional ability to perform multimode optical phase-space displacements---realizable using a beamsplitter and a laser, while the sequential decoder for quantum reading also requires the ability to perform phase-shifting (realizable using a phase plate) and online squeezing (a phase-sensitive amplifier).