Self-coherent phase reference sharing for continuous-variable quantum key distribution

Abstract

We develop a comprehensive framework to model and optimize the performance of CV-QKD with a local local oscillator (LLO), when phase reference sharing and QKD are conjointly implemented with the same hardware. We first analyze the limitations of the only existing approach, called LLO-sequential, and show that it requires high modulation dynamics and can only tolerate small phase noise, leading to expensive hardware requirements. Our main contribution is to introduce two original designs to perform LLO CV-QKD with shared hardware" respectively called LLO-delayline and LLO-displacement, and to study their performance. Both designs rely on a self-coherent approach, in which phase reference information and quantum information are coherently obtained from a single optical wavefront.We show that these designs can lift some important limitations of the existing LLO-sequential approach. The LLO-delayline design can in particular tolerate much stronger phase noise and thus appears as an appealing alternative to LLO-sequential that can moreover be deployed with affordable hardware. We also investigate, with the LLO-displacement design, how phase reference information and quantum information can be multiplexed in a single optical pulse. By studying the trade-off between phase reference recovery and phase noise induced by displacement we however demonstrate that this design can only tolerate low phase noise. On the other hand, the LLO-displacement design has the advantage of minimal hardware requirements and can be applied to multiplex classical and quantum communications, opening practical path towards the development of coherent quantum communications systems compatible with next-generation networks requirements. * Electronic address: adrien.marie@telecom-paristech.fr arXiv:1605.03642v2 [quant-ph] 30 Aug 2016 on the reference frame allows the receiver to more faithfully translate the received physical signals into logical information. It can for example consist in the knowledge of the relative angle between spatial two-dimensional cartesian reference frames [16], in the synchronization of spatially separated clocks [17], or information about the relative phase between two lasers, respectively at emitter and receiver side, when coherent optical communication is performed [15]. This latter problem, phase reference frame sharing considered in the context of CV-QKD, will be the main focus of this article .The problem of sharing a reference frame is specific in the sense that reference frame information constitutes unspeakable information, that can only be shared through physical carriers exchanged between emitter and receiver [18]. On the other hand, it is important to emphasize that although quantum mechanics gives a precise framework to formulate the question of reference frame sharing, in relation with quantum metrology [18], this question can be solved "classically", using macroscopic signals to exchange reference frame information. The type of questions related to phase reference sharing is not whether it is possible, bu...

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“…This additional noise should be added into ε 0 in (3). In [43], a phase noise of 10 −3 was demonstrated experimentally using the scheme proposed in [44]. We expect that a phase noise of 10 −4 could be achieved by further improving the system.…”

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“…where the signal suffers from losses and noise (LO can be also reconstructed locally [33][34][35]). An eavesdropper Eve is presumed to be the cause of both losses and noise within the channel, is able to obtain and store the information about signal states, and is limited in her attacks on the channel only by the laws of physics.…”

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“…Therefore we restrict our claims to the TLO systems. It is worth to mention here that in LLO system, noise from phase estimation error misalign the reference frame that adds additional noise to the excess noise which restricts the performance of CV-QKD system to a few 10s of km [15]. For long distance CV-QKD, TLO scheme delivers secure keys as it is less vulnerable to phase estimation noise and our protocol finds application in high bandwidth and noisy detection.…”