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Simultaneous classical communication and quantum key distribution based on Gaussian modulated coherent states

YoungJun Kim, Young‐Chai Ko

Published Jan 1, 2016• 2 citations
Publisher

Abstract

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.

DOI
10.1587/elex.13.20160680

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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.
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.
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.
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.
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 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.
A novel quantum key distribution (QKD) protocol is proposed and demonstrated. It is based on the transmission of Gaussian-modulated coherent states that are laser pulses containing a few hundred photons .Shot-noise limited coherent (homodyne) detection is used, which makes it possible to achieve high secret-key rates. It remains, in principle, efficient for any value of the line transmission by use of a "reverse reconciliation" technique, which is shown to be secure against individual attacks based on entanglement and quantum memories. The basic idea is to use a reverse reconciliation protocol, that is, Alice attempts to guess what was received by Bob rather than Bob guessing what was sent by Alice. A reverse protocol always gives Alice an advantage over a potential eavesdropper Eve, regardless the line loss. In addition, a specific advantage of using quantum continuous variables is that the high dimensionality of the phase space may be exploited by modulating the field quadratures with a large dynamics, allowing the encoding of several key bits per pulse. This, together with the fact that fast modulation and detection can be achieved, results in a high-rate secret key distribution.