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Results in Physics

Optimizing two-photon quantum scissor with imperfect detectors for continuous variable quantum key distribution

Amene Shafiee, Mojtaba Golshani, Mostafa Motamedifar

Published Jan 11, 2025• 4 citations
Publisher

Abstract

This study presents a closed-form expression that characterizes the output state of a continuous variable quantum key distribution protocol in the presence of both ideal and realistic two photon quantum scissor. Using non-Gaussian computations, we discovered that the ideal quantum scissor improves entanglement between Alice and Bob, even when they are separated by large distances. As a result, the addition of quantum scissors broadens the range of continuous variable quantum key distribution protocols. Additionally, non-ideal quantum scissors' efficiency becomes more significant as the modulation variance of the input state increases. Finally, keep in mind that the benefits of these changes tend to reduce in noisy channels, when the system is inspected under varied amounts of excess noise.

DOI
10.1016/j.rinp.2025.108112

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This study presents a closed-form expression that characterizes the output state of a continuous variable quantum key distribution protocol in the presence of both ideal and realistic two photon quantum scissor. Using non-Gaussian computations, we discovered that the ideal quantum scissor improves entanglement between Alice and Bob, even when they are separated by large distances. As a result, the addition of quantum scissors broadens the range of continuous variable quantum key distribution protocols. Additionally, non-ideal quantum scissors' efficiency becomes more significant as the modulation variance of the input state increases. Finally, keep in mind that the benefits of these changes tend to reduce in noisy channels, when the system is inspected under varied amounts of excess noise.
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In this paper, we derive a closed-form expression for the output state of a CV-QKD protocol in the presence of zero-photon catalysis (ZPC) and a quantum scissor (QS). Then, based on this closed-form solution, we use a direct search algorithm to find the appropriate values of input state and QS parameters, which considerably enhance the range and the fidelity of a CV-QKD protocol. In the special case of pure loss channel, the largest range of the protocol is only 6.5% less than the fundamental limit of repeaterless quantum communication. In addition, examination of the protocol for different values of excess noise, reveals that there is a trade-off between range and fidelity, and a high value of fidelity can be obtained at the cost of a slight reduction in protocol range.
It is known that quantum scissors, as non-deterministic amplifiers, can enhance the performance of Gaussian-modulated continuous-variable quantum key distribution (CV-QKD) in noisy and long-distance regimes of operation. Here, we extend this result to a non-Gaussian CV-QKD protocol with discrete modulation. We show that, by using a proper setting, the use of quantum scissors in the receiver of such discrete-modulation CV-QKD protocols would allow us to achieve positive secret key rates at high loss and high excess noise regimes of operation, which would have been otherwise impossible. This also keeps the prospect of running discrete-modulation CV-QKD over CV quantum repeaters alive.
It is known that quantum scissors, as non-deterministic amplifiers, can enhance the performance of Gaussian-modulated continuous-variable quantum key distribution (CV-QKD) in noisy and long-distance regimes of operation. Here, we extend this result to a non-Gaussian CV-QKD protocol with discrete modulation. We show that, by using a proper setting, the use of quantum scissors in the receiver of such discrete-modulation CV-QKD protocols would allow us to achieve positive secret key rates at high loss and high excess noise regimes of operation, which would have been otherwise impossible. This also keeps the prospect of running discrete-modulation CV-QKD over CV quantum repeaters alive.
In this paper, we examine how the combination of zero-photon catalysis (ZPC) and a quantum scissors (QS) intensifies the range and the fidelity of a continuous-variable quantum key distribution CV-QKD protocol. Using a non-Gaussian calculation, we realized that the QS significantly boosts the range of the protocol and enhances its fidelity at long distances. At negligible values of excess noise, ZPC operation leads to incredibly high fidelity values, even at large distances. In this case, an optimal strength of the ZPC operation exists that maximizes the secure distance of the protocol. Finally, our study of a system with a nonzero value of excess noise reveals that the fidelity generally increases with ZPC, as opposed to the range, which decreases with this Gaussian operation.
We investigate the use of quantum scissors, as candidates for non-deterministic amplifiers, in continuous-variable quantum key distribution. Such devices rely on single-photon sources for their operation and as such, they do not necessarily preserve the Guassianity of the channel. Using exact analytical modeling for the system components, we bound the secret key generation rate for a protocol that uses quantum scissors. We find that, for certain non-zero values of excess noise, such a protocol can reach longer distances than the counterpart with no amplification. This sheds light into the prospect of using quantum scissors as an ingredient in continuous-variable quantum repeaters.