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arXiv:1606.02664 · Physical Review A

Simultaneous classical communication and quantum key distribution using continuous variables

Bing Qi

Published Oct 26, 2016• 57 citations
arXivHTMLPDF

Abstract

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.

DOI
10.1103/physreva.94.042340

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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{10}^{\ensuremath{-}9}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.
Simultaneous quantum and classical communication integrates both continuous variable quantum key distribution and classical coherent optical communication by using the same communication infrastructure. Given its compelling benefits, we proposed a protocol relying on both two-way classical communication and on measurement-device-independent quantum key distribution, in which the superposition-modulation-based coherent states depend on the information bits of both the secret key and on the classical communication ciphertext, which are measured by an untrusted relay node. The proposed scheme strikes a beneficial balance between its level of security and its grade of practicability. Explicitly, on the one hand, the secret key obtained is secure against all attacks on the detectors, and it is eminently suitable for bidirectional classical communication in the metropolitan network as a benefit of its relay-based configuration. Our results show a convincing bit error rate vs secret key rate trade-off for transmission over dozens of kilometers in the quantum channel, hence striking an excellent integrity (bit error rate) vs security trade-off.
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.
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.
Since the working conditions of classical and quantum signals are very different, how to effectively integrate classical and quantum communication networks without affecting their respective performance has become a great challenge.In this paper, we proposed a scheme to realize classical communication and continuous-variable quantum key distribution (CV-QKD) based on frequency-division multiplexing (FDM), and we verified the feasibility of simultaneously realizing CV-QKD and classical optical communication data synchronous transmission scheme under the same infrastructure.We achieved a 0 bit error rate in 50 frames and a 20 Mb/s bit rate for the classical signal and an average secret key rate of around 5.86 × 10 5 bit/s for the quantum signal through a 4 dB fiber channel.This work provides a scheme to establish a QKD channel by only reserving a small passband in the entire optical communication instead of an entire wavelength, increasing efficiency and simplifying the integration of QKD and classical communication.
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.