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Optics Express

Proof-of-principle demonstration of free space semi-quantum key distribution based on the single-state protocol

Naida Mo, Siying Huang, Jindong Wang, Ya‐Fei Yu, Zhengjun Wei, Tianming Zhao, Zhiming Zhang

Published Jul 23, 2024• 2 citations
Publisher

Abstract

Semi-quantum key distribution (SQKD) allows a quantum user and a classical user to share a string of secret keys, providing support for application scenarios that cannot withstand the high cost of quantum resources. In this paper, we propose what we believe to be the first proof-of-principle experimental demonstration of free space SQKD based on the single-state protocol, which is equipped with polarization encoding scheme employing the method of selective modulation. During the half-hour test time for each operation, the overall experiment obtained the original key rate of 107.2 kbps at the repetition frequency of 100 MHz, and the average bit error rate was determined to be 1.65% for CTRL operation and 0.64% for SIFT operation. The experimental results indicate that our system exhibits commendable performance and stability at a low bit error rate that represents a significant initial stride toward the future practical deployment of SQKD systems within free-space channels.

DOI
10.1364/oe.529300

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Semi-quantum key distribution (SQKD) allows a quantum user and a classical user to share a string of secret keys, providing support for application scenarios that cannot withstand the high cost of quantum resources. In this paper, we propose what we believe to be the first proof-of-principle experimental demonstration of free space SQKD based on the single-state protocol, which is equipped with polarization encoding scheme employing the method of selective modulation. During the half-hour test time for each operation, the overall experiment obtained the original key rate of 107.2 kbps at the repetition frequency of 100 MHz, and the average bit error rate was determined to be 1.65% for CTRL operation and 0.64% for SIFT operation. The experimental results indicate that our system exhibits commendable performance and stability at a low bit error rate that represents a significant initial stride toward the future practical deployment of SQKD systems within free-space channels.
Abstract Semi-quantum key distribution (SQKD) is used to establish a string of shared secret keys between a quantum party and a classical party. Here, we report the first proof-of-principle experimental demonstration of SQKD based on the Mirror protocol, which is the most experimentally feasible SQKD protocol, and equipped with time-phase encoding scheme employing the method of selective modulation. The experiment was performed at a repetition frequency of 62.5 MHz and a high raw key rate arrived at 69.8 kbps, and the average quantum bit error rate was found to be 4.56% and 2.78% for the “SWAP-x-Z” ( x∈{01,10}\mathrm{x}\in \{01,10\}x∈{01,10} x ∈ { 01 , 10 } ) and the “CTRL-X”, respectively. The results demonstrate the feasibility of our system, and this study is helpful for future research on SQKD experiments.
Semi-quantum key distribution (SQKD) allows sharing random keys between a quantum user and a classical user, which significantly saves user resources, especially when using the Single-state protocol. However, the operation of the classical user, which involves measurement and resending using the Single-state protocol, presents technical difficulties in experiment and there is a security vulnerability of "tagged" attack in theory. To solve these problems, in our work, based on the Single-state protocol, we propose the "selective modulation" method and successfully implement a phase-encoded semi-quantum key distribution system. The system operates at a frequency of 100MHz and an average photon number of 0.1. The interference contrast achieved 97.45%, the average quantum bit error rate was 1.20%, and the raw key rate reached 88Kbps. Our experimental results demonstrate the feasibility and stability of the proposed phase-encoded SQKD system. Furthermore, we conducted an analysis of the "selective modulation" scheme in terms of quantum state evolution to assess the security of our system and ultimately proved that it can resist "tagged" attack. The classical user of our system requires only two optical devices and operates without relying on full quantum capabilities, thereby enhancing its application potential in quantum networks. This work validates the feasibility of SQKD experiments and provides ideas for future research on SQKD experiments and security studies.
Decoy state semi-quantum key distribution (SQKD) has been proposed as a method aimed at significantly enhancing the security and performance of practical semi-quantum key distribution systems. However, the gap between theory and experiment remains open. Herein, we propose the decoy state setting and experimental scheme for the mirror protocol and conduct the proof-of-principle demonstration experiment of the decoy state mirror protocol. The simulation results, obtained under experimental conditions, demonstrate that no key generation rate can be generated under the conditions of the Gottesman-Lo-Lütkenhaus-Preskill (GLLP) and one-decoy state, while valid key generation rates are achievable within a fiber transmission distance of 19.1 km under the weak and vacuum states. Furthermore, it was experimentally verified that a key generation rate of 406 bits/s can be achieved under the combined conditions of weak and vacuum states and a 10 km fiber channel. As the first, to the best of our knowledge, proof-of-principle demonstration of the decoy state mirror protocol, this study lays a foundation for the practical security analysis of SQKD from an experimental perspective and serves as an important starting point for the practical verification in this field.
Semi-quantum key distribution (SQKD) can share secret keys by using less quantum resource than its fully quantum counterparts, and this likely makes SQKD become more practical and realizable. In this paper, we present a new SQKD protocol by introducing the idea of B92 protocol in fully quantum cryptography into SQKD. In this protocol, the sender Alice just sends one quantum state to the classical Bob and Bob just prepares a fixed state in the preparation process. It is much simpler than the existing SQKD and potentially much easier to be implemented. It can be seen as a semi-quantum version of B92 protocol, compared to the protocol BKM07 as the semi-quantum version of BB84 in fully quantum cryptography. We verify that it is more efficient than the existing single-state SQKD protocols by introducing an efficiency parameter. Specifically, we prove it is secure against a restricted collective attack by computing a lower bound of the key rate in the asymptotic scenario. Then we can find a threshold value of errors such that for all error rates less than this value, the secure key can be definitely established between the legitimate users definitely. We make an illustration of how to compute the threshold value in case the reverse channel is a depolarizing one with parameter [Formula: see text]. Though the threshold value is a little smaller than those of some existing SQKD protocols, it can be comparable to the B92 protocol in fully quantum cryptography.
Quantum key distribution (QKD) has emerged as a revolutionary technique that can ensure unconditionally secure communication between two distant parties, referred to as Alice and Bob, by exploiting the fundamental principles of quantum physics. Here, we report experimental demonstration of a fully automated QKD system based on the BB84 protocol. A weak coherent pulse source is developed to generate stream of polarization encoded single photons. Our QKD system demonstrates a low QBER of ∼1.2% with sifted key generation rate of ∼70 Kbps at an average photon number per pulse ofμ=0.11\mu=0.11μ=0.11. The final secure key rate of ∼33 Kbps is achieved after performing post processing procedures viz. error correction and privacy amplification. The quantum communication link is established continuously for several hours and the performance is evaluated iteratively. The developed QKD system is shown to have the capability of distributing cryptographic keys securely and seamlessly, under practical operating conditions. Furthermore, we have successfully demonstrated unconditionally secure transmission and reception of an image between Alice and Bob connected over an unsecured public channel by utilizing quantum cryptography.
Semi-quantum key distribution (SQKD) can share secret keys by using less quantum resource than its fully quantum counterparts, and this likely makes SQKD become more practical and realizable. In this paper, we present a new SQKD protocol by introducing the idea of B92 into semi-quantum key distribution and prove its unconditional security. In this protocol, the sender Alice just sends one qubit to the classical Bob and Bob just prepares one state in the preparation process. Indeed the classical user's measurement is not necessary either. This protocol can reduce some quantum communication and make it easier to be implemented. It can be seen as the semi-quantum version of B92 protocol, comparing to the protocol BKM2007 as the semi-quantum version of BB84 in fully quantum cryptography. We verify it has higher key rate and therefore is more efficient. Specifically we prove it is unconditionally secure by computing a lower bound of the key rate in the asymptotic scenario from information theory aspect. Then we can find a threshold value of errors such that for all error rates less than this value, the secure key can be established between the legitimate users definitely. We make an illustration of how to compute the threshold value in case of the reverse channel is a depolarizing one with parameter ppp. Though the threshold value is a little smaller than those of some existed SQKD protocols, it can be comparable to the B92 protocol in fully quantum cryptography.