Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:1708.08742 · Physical Review Applied

Noise Analysis of Simultaneous Quantum Key Distribution and Classical Communication Scheme Using a True Local Oscillator

Bing Qi, Charles Ci Wen Lim

Published May 7, 2018• 67 citations
arXivHTMLPDF

Abstract

At first sight, quantum key distribution (QKD) working at single-photon levels seems very different from classical optical communication using strong laser pulses. Surprisingly, in the simultaneous QKD and classical communication (SQCC) protocol, a single, coherent system can both transmit classical information and distribute a quantum key, but implementation has been impeded by its low tolerance of phase noise. The authors identify ``trusted'' noise from the coherent receiver, which cannot be accessed by an eavesdropper, and greatly improve the phase-noise tolerance of the SQCC protocol. Their findings suggest that the SQCC protocol could be truly practical for secure communication.

DOI
10.1103/physrevapplied.9.054008

Related papers

Carrier-phase estimation for simultaneous quantum key distribution and classical communication using a real local oscillator

Tao Wang, Peng Huang, Shiyu Wang +1 more

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.

Physical Review A•Feb 15, 2019•19 citations

Simultaneous classical communication and quantum key distribution using continuous variables

Bing Qi

Presently, classical optical communication systems employing strong laser pulses and quantum key distribution (QKD) systems working at single-photon levels are very different communication modalities. Dedicated devices are commonly required to implement QKD. In this paper, we propose a scheme which allows classical communication and QKD to be implemented simultaneously using the same communication infrastructure. More specially, we propose a coherent communication scheme where both the bits for classical communication and the Gaussian distributed random numbers for QKD are encoded on the same weak coherent pulse and decoded by the same coherent receiver. Simulation results based on practical system parameters show that both deterministic classical communication with a bit error rate of ${10}^{\ensuremath{-}9}$ and secure key distribution could be achieved over tens of kilometers of single-mode fibers. It is conceivable that in the future coherent optical communication network, QKD will be operated in the background of classical communication at a minimal cost.

arXiv:1606.02664•Physical Review A•Oct 26, 2016•57 citations

Simultaneous quantum and classical communication using continuous variable

Bing Qi

Conventionally, classical optical communication systems employing strong laser pulses and quantum key distribution (QKD) systems working at single-photon levels are quite different communication modalities. Dedicated devices are commonly required to implement QKD. Here we show these two can be implemented simultaneously using the same information carriers. More specially, we propose a coherent communication scheme where both the binary bits for a classical communication protocol and Gaussian distributed random numbers for a QKD protocol are encoded on the same weak coherent pulses, and decoded by the same coherent receiver. Simulation results based on realistic system parameters show that both deterministic classical communication with a bit error rate of 10^{-9} and secure key distribution can be achieved over 30km single mode fibers. It is conceivable that in the future coherent optical communication network, QKD is operated in the background of classical communication at negligible cost.

•Jun 8, 2016•1 citation

Optical preamplifier based simultaneous quantum key distribution and classical communication scheme

Hai Zhong, Wei Ye, Xiaodong Wu +1 more

That the simultaneous quantum key distribution and classical communication (SQCC) scheme are combined with the continuous variable quantum key distribution (CVQKD) and the classical communication together, will provide an effective method to implement the simultaneous CVQKD and the classical communication in the existing optical networks in the future. However, superimposing a classical signal on the quantum signal will introduce excess noise into the CVQKD system, thus greatly reducing the performance of the system. In this paper, a novel scheme of SQCC based on optical preamplifier (OPA) is proposed, that is, the OPA is inserted into the receiver to improve the performance of the system. On the one hand, under the condition of the same bit error rate, the amplification of the signal by the OPA can reduce the requirement for the modulation amplitude of the classical signal at the sending end, thereby reducing the noise effect of the classical signal on the quantum signal. On the other hand, the OPA can compensate for the imperfection of the receiver detector. Moreover, in the case of locally generated local oscillator, the amplifier can also amplify the weak phase reference pulse, and thus reducing the phase excess noise caused by the shot noise of the weak phase reference pulse. Numerical simulation results show that the proposed scheme has better performance than the original scheme in the sense of security key rate and transmission distance. These results show that this scheme provides an effective and practical method for the further development and practical application of the SQCC scheme.

Acta Physica Sinica•Jan 1, 2021•6 citations

Enhanced simultaneous quantum-classical communications under composable security

Nicholas Zaunders, Ziqing Wang, Robert Malaney +2 more

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.

arXiv:2505.03145•Physical Review A•Sep 19, 2025•1 citation

Simultaneous quantum and classical communication via multiparameter modulation

Piao Tan, Tao Wang, Huanxi Zhao +3 more

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.

Physical Review A•Mar 25, 2024•7 citations
At first sight, quantum key distribution (QKD) working at single-photon levels seems very different from classical optical communication using strong laser pulses. Surprisingly, in the simultaneous QKD and classical communication (SQCC) protocol, a single, coherent system can both transmit classical information and distribute a quantum key, but implementation has been impeded by its low tolerance of phase noise. The authors identify ``trusted'' noise from the coherent receiver, which cannot be accessed by an eavesdropper, and greatly improve the phase-noise tolerance of the SQCC protocol. Their findings suggest that the SQCC protocol could be truly practical for secure communication.
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.
Presently, classical optical communication systems employing strong laser pulses and quantum key distribution (QKD) systems working at single-photon levels are very different communication modalities. Dedicated devices are commonly required to implement QKD. In this paper, we propose a scheme which allows classical communication and QKD to be implemented simultaneously using the same communication infrastructure. More specially, we propose a coherent communication scheme where both the bits for classical communication and the Gaussian distributed random numbers for QKD are encoded on the same weak coherent pulse and decoded by the same coherent receiver. Simulation results based on practical system parameters show that both deterministic classical communication with a bit error rate of ${10}^{\ensuremath{-}9}$ and secure key distribution could be achieved over tens of kilometers of single-mode fibers. It is conceivable that in the future coherent optical communication network, QKD will be operated in the background of classical communication at a minimal cost.
Conventionally, classical optical communication systems employing strong laser pulses and quantum key distribution (QKD) systems working at single-photon levels are quite different communication modalities. Dedicated devices are commonly required to implement QKD. Here we show these two can be implemented simultaneously using the same information carriers. More specially, we propose a coherent communication scheme where both the binary bits for a classical communication protocol and Gaussian distributed random numbers for a QKD protocol are encoded on the same weak coherent pulses, and decoded by the same coherent receiver. Simulation results based on realistic system parameters show that both deterministic classical communication with a bit error rate of 10^{-9} and secure key distribution can be achieved over 30km single mode fibers. It is conceivable that in the future coherent optical communication network, QKD is operated in the background of classical communication at negligible cost.
That the simultaneous quantum key distribution and classical communication (SQCC) scheme are combined with the continuous variable quantum key distribution (CVQKD) and the classical communication together, will provide an effective method to implement the simultaneous CVQKD and the classical communication in the existing optical networks in the future. However, superimposing a classical signal on the quantum signal will introduce excess noise into the CVQKD system, thus greatly reducing the performance of the system. In this paper, a novel scheme of SQCC based on optical preamplifier (OPA) is proposed, that is, the OPA is inserted into the receiver to improve the performance of the system. On the one hand, under the condition of the same bit error rate, the amplification of the signal by the OPA can reduce the requirement for the modulation amplitude of the classical signal at the sending end, thereby reducing the noise effect of the classical signal on the quantum signal. On the other hand, the OPA can compensate for the imperfection of the receiver detector. Moreover, in the case of locally generated local oscillator, the amplifier can also amplify the weak phase reference pulse, and thus reducing the phase excess noise caused by the shot noise of the weak phase reference pulse. Numerical simulation results show that the proposed scheme has better performance than the original scheme in the sense of security key rate and transmission distance. These results show that this scheme provides an effective and practical method for the further development and practical application of the SQCC scheme.
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.
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.