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Novel Robust Quantum Key Distribution Protocol with Symmetry

Han Yang, Ming Gao, Ping‐Xing Chen, Cheng-Zu Li

Published Aug 1, 2008• 2 citations
Publisher

Abstract

Quantum key distribution (QKD) has been proved unconditionally secure. But noise and imperfection of realistic devices are major difficulties for implementing quantum key distribution. Particularly, the birefringence in optical fiber corresponds to an insuppressible collective unitary transformation on the polarization space. Obviously does not change the permutation symmetry of multiphoton state. By encoding on three 3-photon states with different permutation symmetries, we propose a novel polarization-based protocol, which is robust against an arbitrary degree of collective noise. A clear characteristic of this protocol is that entanglement is absent in principle.

DOI
10.1109/iccsit.2008.129

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Quantum key distribution (QKD) has been proved unconditionally secure. But noise and imperfection of realistic devices are major difficulties for implementing quantum key distribution. Particularly, the birefringence in optical fiber corresponds to an insuppressible collective unitary transformation on the polarization space. Obviously does not change the permutation symmetry of multiphoton state. By encoding on three 3-photon states with different permutation symmetries, we propose a novel polarization-based protocol, which is robust against an arbitrary degree of collective noise. A clear characteristic of this protocol is that entanglement is absent in principle.
We present two polarization-based protocols for quantum key distribution. The protocols encode key bits in noiseless subspaces or subsystems and so can function over a quantum channel subjected to an arbitrary degree of collective noise, as occurs, for instance, due to rotation of polarizations in an optical fiber. These protocols can be implemented using only entangled photon-pair sources, single-photon rotations, and single-photon detectors. Thus, our proposals offer practical and realistic alternatives to existing schemes for quantum key distribution over optical fibers without resorting to interferometry or two-way quantum communication, thereby circumventing, respectively, the need for high precision timing and the threat of Trojan horse attacks.
Standard security proofs of quantum-key-distribution (QKD) protocols often rely on symmetry arguments. In this paper, we prove the security of a three-state protocol that does not possess rotational symmetry. The three-state QKD protocol we consider involves three qubit states, where the first two states $\ensuremath{\mid}{0}_{z}⟩$ and $\ensuremath{\mid}{1}_{z}⟩$ can contribute to key generation, and the third state $\ensuremath{\mid}+⟩=(\ensuremath{\mid}{0}_{z}⟩+\ensuremath{\mid}{1}_{z}⟩)∕\sqrt{2}$ is for channel estimation. This protocol has been proposed and implemented experimentally in some frequency-based QKD systems where the three states can be prepared easily. Thus, by founding on the security of this three-state protocol, we prove that these QKD schemes are, in fact, unconditionally secure against any attacks allowed by quantum mechanics. The main task in our proof is to upper bound the phase error rate of the qubits given the bit error rates observed. Unconditional security can then be proved not only for the ideal case of a single-photon source and perfect detectors, but also for the realistic case of a phase-randomized weak coherent light source and imperfect threshold detectors. Our result in the phase error rate upper bound is independent of the loss in the channel. Also, we compare the three-state protocol with the Bennett-Brassard 1984 (BB84) protocol. For the single-photon source case, our result proves that the BB84 protocol strictly tolerates a higher quantum bit error rate than the three-state protocol, while for the coherent-source case, the BB84 protocol achieves a higher key generation rate and secure distance than the three-state protocol when a decoy-state method is used.
This paper investigates a novel quantum key distribution (QKD) protocol leveraging the principles of quantum decoherence to significantly enhance security against eavesdropping attacks. The core concept involves exploiting the inherent fragility of quantum states due to decoherence, introducing controlled noise to disrupt the eavesdropper's ability to intercept and decode the key. The proposed protocol, termed "Decoherence-Enhanced QKD" (DE-QKD), aims to bolster the security of existing QKD schemes by amplifying the impact of any attempt to observe the quantum key transmission. Mathematical formulations detail the key components, including the polarization encoding, the measurement process, and the key distillation steps, highlighting the protocol's robustness. The analysis demonstrates a substantial increase in security margins compared to conventional QKD protocols, particularly in the presence of imperfect devices and realistic noise conditions. This work contributes to the ongoing research in secure quantum communication and provides a practical pathway for deploying more resilient QKD systems. ---