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Journal of Physics A Mathematical and Theoretical

Multipartite continuous variable quantum communication with entanglement in the middle

Zhaoyuan Zhang, Ronghua Shi, Ying Guo

Published May 30, 2018• 2 citations
Publisher

Abstract

Abstract Multipartite quantum key distribution (QKD) is crucial for quantum communicating and may link massive private information to the complex quantum network protocols. In this paper, we tackle one of the difficulties in multipartite quantum communications by designing a quantum key distribution scheme with improved secret key rates. We suggest an entanglement-based tripartite continuous variable quantum key distribution (CVQKD) scheme for quantum network, where the source in the middle generates tripartite state and distributes the modes of the state to legitimate parties, respectively. We analyze the mutual information among the distributed modes of the tripartite state of protocols involving different attack strategies of the eavesdropper in varied circumstances. Numeric simulation results show that the CVQKD system enables the generations of secret keys against optimal coherent attacks.

DOI
10.1088/1751-8121/aac8cf

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Abstract Multipartite quantum key distribution (QKD) is crucial for quantum communicating and may link massive private information to the complex quantum network protocols. In this paper, we tackle one of the difficulties in multipartite quantum communications by designing a quantum key distribution scheme with improved secret key rates. We suggest an entanglement-based tripartite continuous variable quantum key distribution (CVQKD) scheme for quantum network, where the source in the middle generates tripartite state and distributes the modes of the state to legitimate parties, respectively. We analyze the mutual information among the distributed modes of the tripartite state of protocols involving different attack strategies of the eavesdropper in varied circumstances. Numeric simulation results show that the CVQKD system enables the generations of secret keys against optimal coherent attacks.
We suggest a continuous variable quantum conferencing network scheme with an entangled source in the middle. Here, the source generates a multipartite entangled state and distributes the modes of the state to an arbitrary number of legitimate network users. The entangled modes that were received and measured by the users share mutual information, which is utilized to generate secure conferencing key between users. The scheme is proven secure against collective attacks on both the untrusted source in the middle and all the quantum links. Simulation results show that the presented scheme can achieve high rate secure conferencing for 100 users within a 400 m-radius community or factory area.
A modified continuous-variable quantum key distribution (CVQKD) protocol is proposed by originating the entangled source from a malicious third party Eve in the middle instead of generating it from the trustworthy Alice or Bob. This method is able to enhance the efficiency of the CVQKD scheme attacked by local oscillator (LO) intensity attack in terms of the generated secret key rate in quantum communication. The other indication of the improvement is that the maximum transmission distance and the maximum loss tolerance can be increased significantly, especially for CVQKD schemes based on homodyne detection.
Continuous-variable quantum key distribution (CVQKD) features a high key rate and compatibility with classical optical communication. Developing expandable and efficient CVQKD networks will promote the deployment of large-scale quantum communication networks in the future. This paper proposes a CVQKD network based on the entangled states of an optical frequency comb. This scheme generates Einstein-Podolsky-Rosen entangled states with a frequency comb structure through the process of a type-II optical parametric oscillator. By combining with the scheme of entanglement in the middle, a fully connected CVQKD network capable of distributing secret keys simultaneously can be formed. We analyze the security of the system in the asymptotic case. Simulation results show that under commendable controlling of system loss and noise, the proposed scheme is feasible for deploying a short-distance fully connected CVQKD network. Loss will be the main factor limiting the system's performance. The proposed scheme provides new ideas for a multi-user fully connected CVQKD network.
Continuous-variable quantum key distribution (CVQKD) offers high key rates and compatibility with classical optical communications. Developing scalable and efficient CVQKD networks will facilitate the deployment of large-scale quantum communication networks. This paper proposes a CVQKD network based on the untrusted entanglement states of an optical frequency comb. The scheme generates Einstein-Podolsky-Rosen states with a frequency comb structure via a type-II optical parametric oscillator. By employing the entanglement-in-the-middle scheme, a source-untrusted fully connected CVQKD network capable of distributing secret keys simultaneously can be formed. We analyze the security of the system in the asymptotic and finite-size cases. Simulation results show that with careful control of system loss and noise, the proposed scheme is feasible for deploying a short-distance fully connected CVQKD network. Loss will be the main factor limiting system performance. The proposed scheme offers a new perspective for a multi-user fully connected CVQKD network.
Continuous-variable quantum key distribution (CVQKD) protocols with entanglement in the middle (EM) enable long maximal transmission distances for quantum communications. For the security analysis of the protocols, it is usually assumed that Eve performs collective Gaussian attacks and there is a lack of finite-size analysis of the protocols. However, in this paper we consider the finite-size regime of the EM-based CVQKD protocols by exposing the protocol to collective attacks and coherent attacks. We differentiate between the collective attacks and the coherent attacks while comparing asymptotic key rate and the key rate in the finite-size scenarios. Moreover, both symmetric and asymmetric configurations are collated in a contrastive analysis. As expected, the derived results in the finite-size scenarios are less useful than those acquired in the asymptotic regime. Nevertheless, we find that CVQKD with entanglement in the middle is capable of providing fully secure secret keys taking the finite-size effects into account with transmission distances of more than 30 km.
Multiparty quantum key distribution (QKD) is useful for many applications that involve secure communication or collaboration among multiple parties. While it can be achieved using pairwise QKD, a more efficient approach is to achieve it using multipartite entanglement distributed over quantum networks that connect the multiple parties. Existing studies on multipartite entanglement distribution, however, are not designed for multiparty QKD, and hence do not aim to maximize secret key generation rate. In this paper, we design efficient strategies for multiparty QKD over quantum networks. For 3-party QKD, we derive closed-form expressions for analyzing key distribution over quantum networks. We then use it to develop an efficient strategy for 3-party QKD by packing multiple stars that connect the 3 parties. For the general form of N-party QKD, we develop an approach that packs multiple trees to connect the N parties, while directly incorporating the estimated key rates on network paths. Extensive evaluation of our strategies, in both grid and random graphs, under a wide range of settings, demonstrates that our schemes achieve high key rate, which degrades gracefully when increasing the number of parties.