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Quantum key distribution using a thermal source

Bing Qi

Published Mar 17, 2023• 0 citations
OpenAlex

Abstract

A passive continuous-variable quantum key distribution scheme, where Alice splits the output of a thermal source into two spatial modes, measures one locally and transmits the other mode to Bob after applying attenuation. A secure key can be established based on measurements of the two modes without the use of a random number generator or an optical modulator.

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Passive state preparation in the Gaussian-modulated coherent-states quantum key distribution

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We perform security analysis of a passive continuous-variable quantum key distribution (CV-QKD) protocol by considering the finite-size effect. In the passive CV-QKD scheme, Alice utilizes thermal sources to passively make preparation of quantum state without Gaussian modulations. With this technique, the quantum states can be prepared precisely to match the high transmission rate. Here, both asymptotic regime and finite-size regime are considered to make a comparison. In the finite-size scenario, we illustrate the passive CV-QKD protocol against collective attacks. Simulation results show that the performance of passive CV-QKD protocol in the finite-size case is more pessimistic than that achieved in the asymptotic case, which indicates that the finite-size effect has a great influence on the performance of the single-mode passive CV-QKD protocol. However, we can still obtain a reasonable performance in the finite-size regime by enhancing the average photon number of the thermal state.

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A passive continuous-variable quantum key distribution scheme, where Alice splits the output of a thermal source into two spatial modes, measures one locally and transmits the other mode to Bob after applying attenuation. A secure key can be established based on measurements of the two modes without the use of a random number generator or an optical modulator.
In the Gaussian-modulated coherent-states (GMCS) quantum key distribution (QKD) protocol, Alice prepares quantum states actively: For each transmission, Alice generates a pair of Gaussian-distributed random numbers, encodes them on a weak coherent pulse using optical amplitude and phase modulators, and then transmits the Gaussian-modulated weak coherent pulse to Bob. Here we propose a passive state preparation scheme using a thermal source. In our scheme, Alice splits the output of a thermal source into two spatial modes using a beam splitter. She measures one mode locally using conjugate optical homodyne detectors, and transmits the other mode to Bob after applying appropriate optical attenuation. Under normal conditions, Alice's measurement results are correlated to Bob's, and they can work out a secure key, as in the active state preparation scheme. Given the initial thermal state generated by the source is strong enough, this scheme can tolerate high detector noise at Alice's side. Furthermore, the output of the source does not need to be single mode, since an optical homodyne detector can selectively measure a single mode determined by the local oscillator. Preliminary experimental results suggest that the proposed scheme could be implemented using an off-the-shelf amplified spontaneous emission source.
We propose a continuous-variable quantum secret sharing (CV-QSS) protocol in which the quantum states are prepared passively using a thermal source. In our protocol, one player splits the output of a thermal source into two spatial modes with the help of a beam splitter, then he (or she) measures one of the correlated thermal states and sends the others to the secure station of the adjacent player in sequence after using appropriate optical attenuation, which waives the necessity of employment of high extinction ratio modulators with good stability. Therefore, the proposed protocol provides convenient implementation in QSS framework. Moreover, our scheme is immune to Trojan horse attacks. We derive the security bounds for our protocol against both eavesdroppers and dishonest players. Furthermore, we can achieve tighter bound of QSS distance by considering the finite-size effect, which is more practical than that obtained in the asymptotic limit.
Abstract Continuous-variable measurement-device-independent quantum key distribution (CV-MDI QKD) with Gaussian modulation, or with active state preparation, is immune to all detection-related security loopholes. Here, we first propose a scheme where Alice and Bob both passively prepare quantum states using a true thermal source, which is of lower cost and will contribute to the commercialization of CV-MDI QKD. In particular, Alice and Bob first split the output of a thermal source into two correlated modes via a beam splitter at their respective side. Then they measure one of the two modes using two conjugate homodyne detectors and transmit the other attenuated mode to Charlie independently for the Bell state measurement. Moreover, the homodyne detectors, with bright local oscillators, can act as a filter to selectively measure one single mode, which removes the rigid requirement of a single-mode thermal source. This specific conceptual scheme will contribute to the simplification of the experimental implementation of CV-MDI QKD.
Abstract We analyse a central broadcast continuous variable quantum key distribution protocol in which a beam produced by a thermal source is used to create a secret key between two parties, Alice and Bob. A beam splitter divides the initial beam into a pair of output beams, which are sent to Alice and Bob, with Eve intercepting Bob’s beam. We investigate the protocol in detail, calculating mutual informations through a pair of analytic methods and comparing the results to the outputs of a Monte Carlo simulation of the protocol. In a lossless system, we find that a lower bound on the key rate remains positive in the protocol under a beam splitter attack, provided Bob receives a nonzero proportion of the beam initially sent to him. This suggests that the thermal state protocol could be used experimentally to produce secure keys.
We perform security analysis of a passive continuous-variable quantum key distribution (CV-QKD) protocol by considering the finite-size effect. In the passive CV-QKD scheme, Alice utilizes thermal sources to passively make preparation of quantum state without Gaussian modulations. With this technique, the quantum states can be prepared precisely to match the high transmission rate. Here, both asymptotic regime and finite-size regime are considered to make a comparison. In the finite-size scenario, we illustrate the passive CV-QKD protocol against collective attacks. Simulation results show that the performance of passive CV-QKD protocol in the finite-size case is more pessimistic than that achieved in the asymptotic case, which indicates that the finite-size effect has a great influence on the performance of the single-mode passive CV-QKD protocol. However, we can still obtain a reasonable performance in the finite-size regime by enhancing the average photon number of the thermal state.