Variable Quantum Key Distribution Protocol Research Articles

A Continuous Variable Quantum Key Distribution Protocol Based on Entanglement Swapping of Quasi-Bell Entangled Coherent States

A continuous variable quantum key distribution protocol with entanglement swapping of quasi-Bell entangled coherent states is proposed. As the preliminary step, a sender shares quasi-Bell entangled coherent states with a receiver. After their measurements to distinguish the cases of a zero response, a nonzero even-photon response and an odd-photon response, two legitimate participants fulfill the task of key distribution. The correlations resulting from entanglement swapping of quasi-Bell entangled coherent states and the order rearrangement of transmitted states provide the possibility to protect secret key distribution. In the ideal channel, the success probability increases with the amplitude of the coherent state, and approaches unity when the amplitude of the coherent state is larger than two. However, in the loss channel, the decoherence will introduce error in the generated key, and the error rate increases with the amplitude of the coherent state. When the amplitude of the coherent state is smaller than 0.2 (or so), the error rate approaches zero, although the success probability is less than 0.5 in this case.

A continuous variable quantum deterministic key distribution based on two-mode squeezed states

The distribution of deterministic keys is of significance in personal communications, but the existing continuous variable quantum key distribution protocols can only generate random keys. By exploiting the entanglement properties of two-mode squeezed states, a continuous variable quantum deterministic key distribution (CVQDKD) scheme is presented for handing over the pre-determined key to the intended receiver. The security of the CVQDKD scheme is analyzed in detail from the perspective of information theory. It shows that the scheme can securely and effectively transfer pre-determined keys under ideal conditions. The proposed scheme can resist both the entanglement and beam splitter attacks under a relatively high channel transmission efficiency.

Erratum: Continuous Variable Quantum Key Distribution: Finite-Key Analysis of Composable Security Against Coherent Attacks [Phys. Rev. Lett. 109, 100502 (2012)

We provide a security analysis for continuous variable quantum key distribution protocols based on the transmission of squeezed vacuum states measured via homodyne detection. We employ a version of the entropic uncertainty relation for smooth entropies to give a lower bound on the number of secret bits which can be extracted from a finite number of runs of the protocol. This bound is valid under general coherent attacks, and gives rise to keys which are composably secure. For comparison, we also give a lower bound valid under the assumption of collective attacks. For both scenarios, we find positive key rates using experimental parameters reachable today.

Continuous Variable Quantum Key Distribution: Finite-Key Analysis of Composable Security against Coherent Attacks

We provide a security analysis for continuous variable quantum key distribution protocols based on the transmission of two-mode squeezed vacuum states measured via homodyne detection. We employ a version of the entropic uncertainty relation for smooth entropies to give a lower bound on the number of secret bits which can be extracted from a finite number of runs of the protocol. This bound is valid under general coherent attacks, and gives rise to keys which are composably secure. For comparison, we also give a lower bound valid under the assumption of collective attacks. For both scenarios, we find positive key rates using experimental parameters reachable today.

Tight bounds for the eavesdropping collective attacks on general CV-QKD protocols that involve non-maximally entanglement

A new method to quantify the eavesdropper's accessible information on continuous variable quantum key distribution for protocols implementing homodyne and heterodyne detections is introduced. We have derived upper bounds for the eavesdropping collective attacks on general continuous variable quantum key distribution protocols. Our focus is especially on deriving bounds which are Gaussian optimal for Eve collective attacks that involve non maximally entanglement (i.e. Alice and Bob use non maximally entangled states or non-Gaussian modulation for their quantum key distribution protocols). The new bounds derived are tight for all continuous variable quantum key distribution protocols. We show that the eavesdropper's accessible information is independent of the initial correlation between Alice and Bob modes in reverse reconciliation scheme, while in direct reconciliation scheme, Eve information is given as a function of Alice and Bob initial correlation.

TIGHTENING THE EAVESDROPPING ACCESSIBLE INFORMATION FOR CONTINUOUS VARIABLE QUANTUM KEY DISTRIBUTION PROTOCOLS THAT INVOLVE NONMAXIMALLY ENTANGLEMENT

In this paper, we derive tight bounds for the eavesdropping attacks on continuous variable quantum key distribution (CV-QKD) protocol that involves nonmaximally entangled states. We show that deriving bounds on the eavesdropper's accessible information based on the Heisenberg uncertainty yields upper bounds, but those bounds are not tight. For this reason, we follow different techniques to derive the desired tight bounds. The new bounds are tight for all CV-QKD protocols that involve two-mode entangled state. Our derivations are applied to direct and reverse reconciliation schemes of protocol implementation, respectively.

Phase Coherent States for Enhancing the Performance of Continuous Variable Quantum Key Distribution

In this paper, we present three continuous variable quantum key distribution protocols (named two-, four-, and eight-state protocols) based on the discrete modulation of phase coherent states. We investigate the security of these protocols against the collective eavesdropping attacks and show their performance in a realistic setup by taking into consideration the realistic lossy noisy quantum channels, and the imperfection of detection. We show that the use of phase coherent states gives better performance in terms of noise tolerance, key rate, and achievable distance than that of common linear coherent states.

CONTINUOUS-VARIABLE QUANTUM KEY DISTRIBUTION PROTOCOLS WITH EIGHT-STATE DISCRETE MODULATION

We propose a continuous variable quantum key distribution protocol based on discrete modulation of eight-state coherent states. We present a rigorous security proof against the collective attacks by taking into consideration the realistic lossy and noisy quantum channel, the imperfect detector efficiency, and the detector electronic noise. This protocol shows high tolerance against excess noise and promises to achieve over 100 km distance of optical fiber.

Continuous variable quantum key distribution with modulated entangled states

Quantum key distribution enables two remote parties to grow a shared key, which they can use for unconditionally secure communication over a certain distance. The maximal distance depends on the loss and the excess noise of the connecting quantum channel. Several quantum key distribution schemes based on coherent states and continuous variable measurements are resilient to high loss in the channel, but are strongly affected by small amounts of channel excess noise. Here we propose and experimentally address a continuous variable quantum key distribution protocol that uses modulated fragile entangled states of light to greatly enhance the robustness to channel noise. We experimentally demonstrate that the resulting quantum key distribution protocol can tolerate more noise than the benchmark set by the ideal continuous variable coherent state protocol. Our scheme represents a very promising avenue for extending the distance for which secure communication is possible.

Improvement of secure communication with continuous variable entanglement of squeezed coherent states via heterodyne detection

In this paper, we propose a continuous variable quantum key distribution protocol based on entanglement of a squeezed coherent state and reverse reconciliation. We present a rigorous security proof against individual and collective attacks with realistic lossy, noisy quantum channels, imperfect detector efficiency and detector electronic noise. This protocol is promising for convenient, high-speed operation at link distances to over 50 km. The setup can be further improved in terms of key generation rate and distance by inserting a noiseless phase-sensitive amplifier at the legitimate receiver Bob's input in order to compensate for the inherent imperfection of heterodyne detection.

Security of a discretely signaled continuous variable quantum key distribution protocol for high rate systems

We propose a continuous variable based quantum key distribution protocol that makes use of discretely signaled coherent light and reverse error reconciliation. We present a rigorous security proof against collective attacks with realistic lossy, noisy quantum channels, imperfect detector efficiency, and detector electronic noise. This protocol is promising for convenient, high-speed operation at link distances up to 50 km with the use of post-selection.