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Frontiers in Optics

Optical Hybrid-based Optimal Receiver Design for Entanglement-Assisted Communication

Rahul Kumar Bhadani, Ivan B. Djordjević

Published Jan 1, 2021• 0 citations
Publisher

Abstract

We propose an optical hybrid (OH) based receiver to discriminate phase-shift-keying modulated information that is transmitted using entanglement-assisted (EA) communication. Our numerical result demonstrates that OH-based receivers perform 10% better in terms of error probability and approximately 50% in terms of Shannon’s capacity compared to the previously proposed receiver design.

DOI
10.1364/fio.2021.ftu2d.2

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IEEE Access•Jan 1, 2022•1 citation
We propose an optical hybrid (OH) based receiver to discriminate phase-shift-keying modulated information that is transmitted using entanglement-assisted (EA) communication. Our numerical result demonstrates that OH-based receivers perform 10% better in terms of error probability and approximately 50% in terms of Shannon’s capacity compared to the previously proposed receiver design.
The use of pre-shared entanglement in entanglement-assisted communication offers a superior alternative to classical communication, especially in the photon-starved regime and highly noisy environments. In this paper, we analyze the performance of several low-complexity receivers that use optical parametric amplifiers. The simulations demonstrate that receivers employing an entanglement-assisted scheme with phase-shift-keying modulation can outperform classical capacities. We present a 2x2 optical hybrid receiver for entanglement-assisted communication and show that it has a roughly 10% lower error probability compared to previously proposed optical parametric amplifier-based receivers for more than 10 modes. However, the capacity of the optical parametric amplifier-based receiver exceeds the Holevo capacity and the capacities of the optical phase conjugate receiver and 2x2 optical hybrid receiver in the case of a single mode. The numerical findings indicate that surpassing the Holevo and Homodyne capacities does not require a large number of signal-idler modes. Furthermore, we find that using unequal priors for BPSK provides roughly three times the information rate advantage over equal priors.
An important problem in quantum information theory is finding the best possible performance of the optical communication channel employing suitable codewords, receiver design, and constellation optimization techniques. Many receiver designs have been studied in the past to discriminate Phase-Shift Keying (PSK) quantum states that are used to encode information before transmitting over the communication channel. Among many types of quantum states, there has been significant work on the use of coherent states for encoding information. Previous work has sought to improve the communication performance in terms of various metrics such as error probability of state discrimination and capacities by employing a number of quantum states such as coherent states and squeezed-displaced states. In this thesis, we provide optimal receiver design employing coherent states and squeezed-displaced states to maximize the mutual information and lower the error probability of state discrimination. In the case of pure coherent states, we derive an alternative channel capacity of phase-shift keying coherent state with a realizable displacement receiver by maximizing mutual information over symbol priors and pre-detection displacement. We find that the capacity is higher than the capacity achieved by maximizing mutual information over symbol prior but with zero displacements. The overall scheme demonstrates designing an improved, yet easy-to-implement receiver for better communication performance by tuning it at different photon number regime. We also explore the use of squeezing operations with a displacement receiver for state discrimination. Our calculation demonstrates that we see no performance improvement in terms of the probability of error of state discrimination or mutual information using displacement receivers when optimal squeezing on the transmitter side is used. In addition, we also study the receiver design scheme for QPSK modulation where squeezing is employed at the receiver side. We find that using the squeezing operation on the receiver side provides an advantage in terms of increased mutual information for the low-photon number regime compared to when no squeezing is used. In the later part of the thesis, we study entanglement-assisted communication using two-mode squeezing vacuum. The use of pre-shared entanglement in entanglement-assisted communication provides a superior alternative to classical communication specifically in the low brightness regime and highly noisy environment. In this thesis, we analyze the performance of a few low-complexity receivers that employ optical parametric amplifiers. In the simulation, we demonstrate that receiver designs with an entanglement-assisted scheme using phase-shift-keying modulation can outperform classical capacities. We describe a newly proposed 2x2 optical hybrid receiver for entanglement-assisted communication whose performance is roughly 10% better in terms of error probability as compared to previously proposed optical parametric amplifier-based receivers. Further, we find that using unequal priors for BPSK provides approximately three times the advantage over equal priors in terms of information rate.
Entanglement assisted (EA) communication represents an interesting alternative to classical communication, in particular in low-brightness and highly noisy regime when it outperforms significantly corresponding classical counterpart in terms of the channel capacity. Even though that the EA capacity is known for decades the optimum quantum receiver has not been determined yet. In this paper, we propose several low-complexity quantum receivers outperforming recently proposed receivers employing the optical parametric amplifier as a basic building block. We demonstrate by simulations that the capacity of the proposed EA schemes, employing Gaussian modulation and the proposed low-complexity joint receivers, can significantly outperform both the Holevo capacity and classical homodyne and heterodyne channel capacities.
Entanglement assisted (EA) communication has been advocated by numerous authors as a potential alternative to classical communications, in particular in noisy and low-brightness regime. In this paper, we propose an EA scheme employing the optical phase-conjugation (OPC) on transmitter side. We show that the proposed EA communication system, with the transmitter side OPC, significantly outperforms its classical counterpart in low-brightness and highly noisy regime, while employing a classical coherent detection scheme for two-dimensional demodulation. Moreover, the capacity of the proposed EA scheme is significantly higher than EA repetition-BPSK, homodyne, heterodyne, and Holevo capacities. Finally, the proposed EA scheme outperforms the corresponding EA scheme with OPC placed on a receiver side.
Many receiver designs have been studied in the past to discriminate Phase-Shift Keying (PSK) quantum states that are used to encode information before transmitting over the communication channel. Among many types of quantum states, there has been significant work on the use of coherent states for encoding information. Previous work has sought to improve the communication performance in terms of various metrics such as error probability of state discrimination and capacities by employing more complex quantum states such as squeezed-displaced states. One of the simplest receivers for state discrimination is the displacement receiver. However, our calculation demonstrates that when we use optimal parameters for a displacement receiver, squeezed-displaced states might not be necessary, and merely using coherent states suffice. We see no performance improvement in terms of probability of error of state discrimination as well as mutual information using displacement receivers when optimal squeezing parameters are used with squeezing operation on the transmitter side for BPSK and QPSK. In addition, we also study the receiver design scheme for QPSK modulation where squeezing is employed at the receiver side. We find that using squeezing operation on the receiver side just before detection provides an advantage in terms of increased mutual information for the low-photon regime compared to when no squeezing is used. For all other cases, squeezing offers no additional advantage.