Abstract
Most quantum key distribution (QKD) protocols can be classified as either a discrete-variable (DV) protocol or continuous-variable (CV) protocol, based on how classical information is being encoded. We propose a protocol that combines the best of both worlds – the simplicity of quantum state preparation in DV-QKD together with the cost-effective and high-bandwidth of homodyne detectors used in CV-QKD. Our proposed protocol has two highly practical features: (1) it does not require the honest parties to share the same reference phase (as required in CV-QKD) and (2) the selection of decoding basis can be performed after measurement. We also prove the security of the proposed protocol in the asymptotic limit under the assumption of collective attacks. Our simulation suggests that the protocol is suitable for secure and high-speed practical key distribution over metropolitan distances.
Highlights
Quantum key distribution (QKD) provides an information-theoretic method to exchange secret keys between distant parties, whose security is promised by the laws of quantum mechanics [1,2,3]
A key advantage of our protocol over most existing CV-QKD protocols is that the need for a common phase reference between Alice and Bob is completely eliminated, which greatly simplifies the system configuration
Our security analysis framework allows us to work in the trusted device scenario which permits us to incorporate characterised device imperfections into our security analysis
Summary
Quantum key distribution (QKD) provides an information-theoretic method to exchange secret keys between distant parties, whose security is promised by the laws of quantum mechanics [1,2,3]. One prominent example is the GG02 protocol proposed by Grosshans and Grangier [10], which requires two key assumptions: (1) the users are able to perform ideal Gaussian modulation and that (2) their local oscillators (LOs) are coordinated/calibrated (in terms of relative phase and wavelength) While in theory these conditions are well defined and understood, their practical implementations are not straightforward. Given the pros and cons of DV-QKD and CV-QKD, it is of interest to study hybrid QKD schemes that tap on the best of both approaches This raises the question whether one could combine discrete encoding with continuous decoding without a common phase reference, using the transmission of randomly prepared single photons like in decoy-state BB84 QKD.
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