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Journal of the Optical Society of America B

Free-space quantum secure direct communication based on decoherence-free space

Zikai Gao, Mingfeng Ma, Tianqi Liu, Jiada Long, Tao Li, Zhenhua Li

Published Aug 10, 2020• 10 citations
Publisher

Abstract

We propose a free-space quantum secure direct communication protocol by using hyper-encoded single photons. The communication parties can securely exchange private information in a deterministic way. In this protocol, single photons are encoded simultaneously by both the polarization and spatial-mode degrees of freedom that constitute a decoherence-free space. The detrimental effect introduced by either reference-frame misalignment or practical channel rotational noise is passively suppressed. Finally, the security of our protocol against classical individual attacks is proved by quantum mutual information.

DOI
10.1364/josab.397973

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In this paper, we propose a new controlled quantum secure direct communication (CQSDC) protocol with single photons in both polarization and spatial-mode degrees of freedom. Based on the defined local collective unitary operations, the sender’s secret messages can be transmitted directly to the receiver through encoding secret messages on the particles. Only with the help of the third side, the receiver can reconstruct the secret messages. Each single photon in two degrees of freedom can carry two bits of information, so the cost of our protocol is less than others using entangled qubits. Moreover, the security of our QSDC network protocol is discussed comprehensively. It is shown that our new CQSDC protocol cannot only defend the outsider eavesdroppers’ several sorts of attacks but also the inside attacks. Besides, our protocol is feasible since the preparation and the measurement of single photon quantum states in both the polarization and the spatial-mode degrees of freedom are available with current quantum techniques.
Quantum Secure Direct Communication (QSDC) is a promising approach for secure information exchange. This paper proposes an efficient and secure four-party QSDC scheme utilizing hyperentangled Bell states in the polarization degree of freedom, the first longitudinal momentum degree of freedom and the second longitudinal momentum degree of freedom. The four participants can perform different unitary operations to independently encode their secret messages onto photons in three degrees of freedom, subsequently transmitting them directly through the quantum channel. In this proposed protocol, each degree of freedom of the photon can effectively carry two bits of information. Each round of transmission by a photon enables the four legitimate participants to obtain six classical bits of information. Notably, when compared to other photons based single-degree-of-freedom QSDC network protocols, the capacity of proposed QSDC protocol is tripled. Therefore, it significantly enhances the information transmission capability. Furthermore, comprehensive security analysis shows that our QSDC network protocol can withstand various attacks from external eavesdroppers.
Abstract Security loopholes exploiting the flaws of practical apparatus, especially non-ideal photon detectors, are pressing issues in practical quantum communication. We propose a simple quantum secure direct communication protocol based on single-photon Bell-state measurement and remove side-channel attacks on photon detectors. This quantum communication protocol in principle works in a deterministic way, and it does not require the two-photon interference of photons from independent sources. The single-photon Bell-state measurement with a unity efficiency can be constructed with only linear optics, which significantly simplifies its experimental implementation. Furthermore, we prove that our quantum secure direct communication protocol is immune to general detector-side-channel attacks.
In this paper, we propose the first semiquantum secure direct communication (SQSDC) protocol which is based on single photons in both polarization and spatial-mode degrees of freedom. This protocol doesn't require both communicants to possess quantum capabilities, and is feasible for the direct communication circumstance where one communicant is quantum and the other is classical. We validate the complete robustness of the transmissions of single photons between two communicants in Steps 1 and 2 of this protocol in detail. It turns out that during these transmissions, if Eve wants not to be detected by two communicants, she will obtain nothing useful. The security of the whole protocol is guaranteed by the complete robustness of the transmissions of single photons between two communicants in Steps 1 and 2 of this protocol and the subsequent classical one-time pad encryption process. In this protocol, one single photon with two degrees of freedom can carry two private bits from the message owner, so compared with the existing SQSDC protocols based on single photons in one degree of freedom, its quantum communication capacity is doubled.
We report an experimental implementation of free-space quantum secure direct communication based on single photons. The quantum communication scheme uses phase encoding, and the asymmetric Mach–Zehnder interferometer is optimized so as to automatically compensate phase drift of the photons during their transitions over the free-space medium. At a 16 MHz pulse repetition frequency, an information transmission rate of 500 bps over a 10 m free space with a mean quantum bit error rate of 0.49 % ± 0.27 % is achieved. The security is analyzed under the scenario that Eve performs the collective attack for single-photon state and the photon number splitting attack for multi-photon state in the depolarizing channel. Our results show that quantum secure direct communication is feasible in free space.