Belief propagation with quantum messages for quantum-enhanced classical communications

Abstract For space-based laser communications, when the mean photon number per received optical pulse is much smaller than one, there is a large gap between communications capacity achievable with a receiver that performs individual pulse-by-pulse detection, and the quantum-optimal “joint-detection...

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Autores principales:	Narayanan Rengaswamy, Kaushik P. Seshadreesan, Saikat Guha, Henry D. Pfister
Formato:	article
Lenguaje:	EN
Publicado:	Nature Portfolio 2021
Materias:	Physics QC1-999 Electronic computers. Computer science QA75.5-76.95
Acceso en línea:	https://doaj.org/article/e8dbcba452f94dcaa089ba3ddba905ec
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spelling	oai:doaj.org-article:e8dbcba452f94dcaa089ba3ddba905ec2021-12-02T16:04:23ZBelief propagation with quantum messages for quantum-enhanced classical communications10.1038/s41534-021-00422-12056-6387https://doaj.org/article/e8dbcba452f94dcaa089ba3ddba905ec2021-06-01T00:00:00Zhttps://doi.org/10.1038/s41534-021-00422-1https://doaj.org/toc/2056-6387Abstract For space-based laser communications, when the mean photon number per received optical pulse is much smaller than one, there is a large gap between communications capacity achievable with a receiver that performs individual pulse-by-pulse detection, and the quantum-optimal “joint-detection receiver” that acts collectively on long codeword-blocks of modulated pulses; an effect often termed “superadditive capacity”. In this paper, we consider the simplest scenario where a large superadditive capacity is known: a pure-loss channel with a coherent-state binary phase-shift keyed (BPSK) modulation. The two BPSK states can be mapped conceptually to two non-orthogonal states of a qubit, described by an inner product that is a function of the mean photon number per pulse. Using this map, we derive an explicit construction of the quantum circuit of a joint-detection receiver based on a recent idea of “belief-propagation with quantum messages” (BPQM). We quantify its performance improvement over the Dolinar receiver that performs optimal pulse-by-pulse detection, which represents the best “classical” approach. We analyze the scheme rigorously and show that it achieves the quantum limit of minimum average error probability in discriminating 8 (BPSK) codewords of a length-5 binary linear code with a tree factor graph. Our result suggests that a BPQM receiver might attain the Holevo capacity of this BPSK-modulated pure-loss channel. Moreover, our receiver circuit provides an alternative proposal for a quantum supremacy experiment, targeted at a specific application that can potentially be implemented on a small, special-purpose, photonic quantum computer capable of performing cat-basis universal qubit logic.Narayanan RengaswamyKaushik P. SeshadreesanSaikat GuhaHenry D. PfisterNature PortfolioarticlePhysicsQC1-999Electronic computers. Computer scienceQA75.5-76.95ENnpj Quantum Information, Vol 7, Iss 1, Pp 1-12 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Physics QC1-999 Electronic computers. Computer science QA75.5-76.95
spellingShingle	Physics QC1-999 Electronic computers. Computer science QA75.5-76.95 Narayanan Rengaswamy Kaushik P. Seshadreesan Saikat Guha Henry D. Pfister Belief propagation with quantum messages for quantum-enhanced classical communications
description	Abstract For space-based laser communications, when the mean photon number per received optical pulse is much smaller than one, there is a large gap between communications capacity achievable with a receiver that performs individual pulse-by-pulse detection, and the quantum-optimal “joint-detection receiver” that acts collectively on long codeword-blocks of modulated pulses; an effect often termed “superadditive capacity”. In this paper, we consider the simplest scenario where a large superadditive capacity is known: a pure-loss channel with a coherent-state binary phase-shift keyed (BPSK) modulation. The two BPSK states can be mapped conceptually to two non-orthogonal states of a qubit, described by an inner product that is a function of the mean photon number per pulse. Using this map, we derive an explicit construction of the quantum circuit of a joint-detection receiver based on a recent idea of “belief-propagation with quantum messages” (BPQM). We quantify its performance improvement over the Dolinar receiver that performs optimal pulse-by-pulse detection, which represents the best “classical” approach. We analyze the scheme rigorously and show that it achieves the quantum limit of minimum average error probability in discriminating 8 (BPSK) codewords of a length-5 binary linear code with a tree factor graph. Our result suggests that a BPQM receiver might attain the Holevo capacity of this BPSK-modulated pure-loss channel. Moreover, our receiver circuit provides an alternative proposal for a quantum supremacy experiment, targeted at a specific application that can potentially be implemented on a small, special-purpose, photonic quantum computer capable of performing cat-basis universal qubit logic.
format	article
author	Narayanan Rengaswamy Kaushik P. Seshadreesan Saikat Guha Henry D. Pfister
author_facet	Narayanan Rengaswamy Kaushik P. Seshadreesan Saikat Guha Henry D. Pfister
author_sort	Narayanan Rengaswamy
title	Belief propagation with quantum messages for quantum-enhanced classical communications
title_short	Belief propagation with quantum messages for quantum-enhanced classical communications
title_full	Belief propagation with quantum messages for quantum-enhanced classical communications
title_fullStr	Belief propagation with quantum messages for quantum-enhanced classical communications
title_full_unstemmed	Belief propagation with quantum messages for quantum-enhanced classical communications
title_sort	belief propagation with quantum messages for quantum-enhanced classical communications
publisher	Nature Portfolio
publishDate	2021
url	https://doaj.org/article/e8dbcba452f94dcaa089ba3ddba905ec
work_keys_str_mv	AT narayananrengaswamy beliefpropagationwithquantummessagesforquantumenhancedclassicalcommunications AT kaushikpseshadreesan beliefpropagationwithquantummessagesforquantumenhancedclassicalcommunications AT saikatguha beliefpropagationwithquantummessagesforquantumenhancedclassicalcommunications AT henrydpfister beliefpropagationwithquantummessagesforquantumenhancedclassicalcommunications
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Belief propagation with quantum messages for quantum-enhanced classical communications

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