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Physical Review A

Simultaneous quantum and classical communication via multiparameter modulation

Piao Tan, Tao Wang, Huanxi Zhao, Zicong Tan, Peng Huang, Guihua Zeng

Published Mar 25, 2024• 7 citations
Publisher

Abstract

Classical and quantum communication protocols share similarities in terms of signal modulation, transmission, and reception, providing a basis for their integration. The integration of these protocols can lead to high-efficiency and low-cost performance by utilizing a single set of communication infrastructures to simultaneously achieve continuous-variable quantum key distribution and classical communication on a single wavelength. In this paper, we propose a simultaneous quantum and classical communication (SQCC) protocol based on multiparameter modulation, which combines pulse position modulation (PPM) for classical communication and Gaussian-distributed modulation (GM) for quantum key distribution, named GMCS-PPM-SQCC protocol. Classical information is transmitted using the arrival time parameter of the coherent state, while quantum key information is distributed through the two quadrature components of the coherent state. Coherent detection is used to detect all three parameters, and different data processing schemes are utilized to extract the corresponding information. We verified the feasibility of the protocol through simulations, discussed its secure transmission distance, bit error rate, and secret key rate in realistic scenarios. Our protocol has better phase noise tolerance than traditional SQCC protocol. It can further facilitates the integration of classical and quantum communication, and contributes to the deployment and application of QKD.

DOI
10.1103/physreva.109.032621

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Classical and quantum communication protocols share similarities in terms of signal modulation, transmission, and reception, providing a basis for their integration. The integration of these protocols can lead to high-efficiency and low-cost performance by utilizing a single set of communication infrastructures to simultaneously achieve continuous-variable quantum key distribution and classical communication on a single wavelength. In this paper, we propose a simultaneous quantum and classical communication (SQCC) protocol based on multiparameter modulation, which combines pulse position modulation (PPM) for classical communication and Gaussian-distributed modulation (GM) for quantum key distribution, named GMCS-PPM-SQCC protocol. Classical information is transmitted using the arrival time parameter of the coherent state, while quantum key information is distributed through the two quadrature components of the coherent state. Coherent detection is used to detect all three parameters, and different data processing schemes are utilized to extract the corresponding information. We verified the feasibility of the protocol through simulations, discussed its secure transmission distance, bit error rate, and secret key rate in realistic scenarios. Our protocol has better phase noise tolerance than traditional SQCC protocol. It can further facilitates the integration of classical and quantum communication, and contributes to the deployment and application of QKD.
Classical communication and quantum key distribution (QKD) share similarities in signal modulation, transmission, and reception, providing a foundation for their integration. This paper proposes a novel protocol for simultaneous quantum and classical communication in short-distance Continuous-Variable QKD (CV-QKD). The protocol employs polarization-state encoding of classical information with weak coherent states, allowing for the concurrent transmission of quantum and classical data without the need for classical optical pulses. A noise model is established to analyze the system’s excess noise under varying modulation variances, along with the performance of both classical and quantum communication. Simulation results indicate that our proposed protocol can achieve a secure key rate of no less than 1.05Mbps over a distance of 20km.
We propose a terahertz continuous-variable quantum key distribution protocol using pulse position modulation, which enables simultaneous quantum and classical communication for inter-satellite links. In this scheme, classical information is conveyed through the relative positioning of encoded pulses while quantum information is encoded using Gaussian modulation to generate thermal terahertz (THz) signals. Coherent detection is employed to measure all the relevant parameters. Extensive multi-parameter simulations were conducted to validate the protocol, examining the bit error rate, secret key rate, and transmission distance under varying pulse position modulation (PPM) settings and other parameters. The results demonstrate that the protocol is feasible and represents an effective method for quantum key distribution. The proposed approach offers a promising pathway for the deployment of inter-satellite quantum communication networks.
Displacement-based simultaneous quantum-classical communications (SQCC) protocols, as originally proposed, are generally incompatible with the majority of useful quantum communication schemes, such as entanglement distribution or repeater-based quantum key distribution: direct measurement of the classical signal also measures and destroys the quantum state, leaving point-to-point Gaussian quantum key distribution as the only quantum communication scheme amenable to integration with SQCC. In this work, we apply the classically-modulated quantum communication protocol proposed by Zaunders and Ralph [arXiv:2606.03181v3] to circumvent this issue and demonstrate the distribution of continuous-variable Gaussian entanglement simultaneously with classical information. We characterise the quality of the distributed entangled state and outline how the scheme is suitable for use in repeater-based networks. Lastly, we compute the secret key generation rate of the Gaussian CMQC scheme in the point-to-point case and compare it to the equivalent point-to-point SQCC protocol.
Simultaneous quantum-classical communications (SQCC) protocols are a family of continuous-variable quantum key distribution (CV-QKD) protocols which allow for quantum and classical symbols to be integrated concurrently on the same optical pulse and mode. In this work, we present a revised analysis of simultaneous quantum-classical communications in Gaussian-modulated coherent-state CV-QKD protocols. We address security concerns inherently associated with SQCC schemes and provide an updated model of the coupling between the classical and quantum channels. We provide evidence for our model via Monte Carlo simulation. We compute the performance of our revised SQCC protocol in terms of the secret-key generation rate optimised over free parameters and demonstrate improved quantum efficiency for a given classical bit-error rate. Lastly, we extend our analysis into the finite-key regime, where we propose a scheme for composably-secure SQCC under realistic operating conditions and demonstrate that our scheme retains the advantage in quantum performance over previous models.
We propose a new quantum communication scheme using quantum coherent states. In our scheme, classical information and the secret key are transmitted simultaneously without any loss of secret key rate performance, while only the secret key is transmitted in the conventional protocol. In our protocol, classical information is first modulated by pulse amplitude modulation (PAM). The secret key is then mapped by random Gaussian modulation and is added to the PAM symbol. The receiver decodes the classical information, treating the Gaussian signal as additive noise. The classical symbol is discarded from the received state after successive decoding of the classical information, and the secret key is then distilled by conventional protocol. We demonstrate that after the classical symbol is discarded, the remaining system is identical to the conventional quantum key distribution system. Our proposed scheme provides the same secret key rate as that of the conventional quantum key distribution system and provides an additional data rate of classical information.
The simultaneous quantum and classical communication (SQCC) protocol is an appealing protocol since it allows continuous-variable quantum key distribution (CV-QKD) and classical communication to be implemented simultaneously by using the same communication infrastructure and on a single wavelength. However, the main challenge of the SQCC protocol is its low tolerance of phase noise, limiting the transmission distance under the real local oscillator (LO) design. To eliminate the phase drift without the aid of the reference signal, the classical carrier phase estimation (CPE) algorithm in the field of coherent optical communication is employed for phase recovery and data extraction. Besides, the power of the residual phase noise in classical communication and the power of the excess phase noise in CV-QKD are derived, including the effects of the employed laser linewidth, the transversal filter length, and the classical signal power. On this basis, the performances of the SQCC protocol under the trusted and the untrusted phase noise model are discussed, respectively. Our work confirms the feasibility of the CPE algorithm in the SQCC protocol and demonstrates the conditions required for this protocol to operate on a coherent optical communication system.