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arXiv:2201.13399 · Journal of Lightwave Technology

Polarization Diverse True Heterodyne Receiver Architecture for Continuous Variable Quantum Key Distribution

Daniel Pereira, Armando N. Pinto, Nuno A. Silva

Published Nov 3, 2022• 13 citations
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Abstract

We present a polarization diverse receiver architecture for continuous variables quantum key distribution. We demonstrate experimentally that our system is capable of reliably achieving theoretical security against collective attacks, even under very adverse random polarization drift scenarios, and is capable of functioning indefinitely without any user input. We show that, in a similar scenario, a standard CV-QKD system without polarization diversity cannot distribute keys securely. Our receiver architecture forgoes the need for any polarization matching calibrations or feedback loops and is usable in any locally generated local oscillator key distribution system. A theoretical study on the security impact of polarization drift is presented, based on which we show that, when using our polarization diverse receiver, it is possible to achieve the performance of a channel with zero polarization drift.

DOI
10.1109/jlt.2022.3216754

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We present a polarization diverse receiver architecture for continuous variables quantum key distribution. We demonstrate experimentally that our system is capable of reliably achieving theoretical security against collective attacks, even under very adverse random polarization drift scenarios, and is capable of functioning indefinitely without any user input. We show that, in a similar scenario, a standard CV-QKD system without polarization diversity cannot distribute keys securely. Our receiver architecture forgoes the need for any polarization matching calibrations or feedback loops and is usable in any locally generated local oscillator key distribution system. A theoretical study on the security impact of polarization drift is presented, based on which we show that, when using our polarization diverse receiver, it is possible to achieve the performance of a channel with zero polarization drift.
Abstract The practical deployment of Continuous Variables Quantum Key Distribution (CV-QKD) systems benefits from existing optical fiber telecommunication infrastructures. However, optical fibers introduce random variations in the state of polarization, which degrades the system's performance.We consider a CV-QKD system featuring a polarization diversity heterodyne receiver and the constant modulus algorithm (CMA) to compensate for the polarization drifts in the quantum channel. Our setup can effectively realign Alice's quantum signal with Bob's local oscillator for polarization drift variances below 10−1010^{-10}10−10 .This value is compatible with most experimental implementations, allowing for accurate estimation of the channel transmission and excess noise parameters. This validates the approximation of real-world implementations under polarization drift to an ideal scenario without polarization drift, ensuring that the security proof remains applicable for polarization drift variances below $ 10^{-10} $.Our results establish operational limits for passive polarization drift compensation using a polarization diversity receiver combined with digital CMA.This enables long-term stability in \linebreak CV-QKD systems, eliminating the need for active polarization controllers and manual adjustments.
Continuous-variable quantum key distribution (CV-QKD) provides a theoretical unconditionally secure solution to distribute symmetric keys among users connected through a communication channel. However, polarization drift in standard optical fibres can pose a considerable impairment, as it will degrade the efficiency of the coherent detection scheme if not compensated. In this work, we present a novel receiver configuration for CV-QKD that allows for passive polarization drift compensation. The presented results show that our detection system can effectively compensate random polarization drift even in very adverse scenarios.
In this Letter we present a discrete modulated, continuous variables quantum key distribution implementation using two probabilistically shaped, 128-symbol, amplitude and phase shift keying constellations. At Bob's detection side, a polarization diverse, true heterodyne receiver architecture is implemented for symbol recovery. We demonstrate experimentally that our system is capable of achieving security against collective attacks, while using accessible, telecom-grade material, and of functioning for an indefinitely long period of time at distances in excess of 185 km, in the asymptotic regime.
Continuous-variable quantum key distribution (CV-QKD) using coherent states and heterodyne detection enables secure quantum communication based on technology that has large similarities to coherent optical telecommunication. Yet, practical implementations of coherent receivers used in both technologies encounter device imperfections, which for CV-QKD are often not addressed in security proofs. Here, we present a theoretical framework that rigorously accounts for imperfect heterodyne measurements arising from phase and amplitude imbalances in the coherent (heterodyne) receiver. Focusing on collective attacks, we establish a finite-size security proof that reveals how measurement imperfections limit the distance over which a positive key rate is achievable. To mitigate these effects, we propose a local transformation during classical post-processing. We validate our approach experimentally on a CV-QKD system with an imperfect coherent receiver, underscoring its potential for scalable, cost-effective CV-QKD with photonic integrated receivers in which phase and amplitude imbalances naturally appear through manufacturing tolerances.
Practical implementations of Continuous Variable (CV) Quantum Key Distribution (QKD) systems can be performed over the existing optical fiber telecommunication infrastructure. However, optical fibers suffer from random variations in the state of polarization affecting the performance of the system. In this work, we study the impact of the polarization drift on the performance of a CV-QKD setup with a polarization diversity receiver, in which the polarization drift is pre-compensated on Alice’s side. We show that pre-compensating for the polarization drift can successfully realign Alice’s and Bob’s raw signal, without affecting the excess noise, up to a polarization drift variance of 10−10, compatible with most practical implementations.
In quantum secure communication, continuous-variable quantum key distribution (CV-QKD) using a true local oscillator (LO) located at the receiver has been proposed to remove side-channel-attack vulnerabilities and reduce excess noise, but implementations have been confined to the lab. The authors demonstrate CV-QKD with a receiver-based true LO over a deployed fiber network, with coexistent classical communications. This represents a substantial technical and engineering advance over prior tabletop demonstrations.