Multiparty quantum anonymous voting with discrete modulated coherent states and an optical frequency comb.

A key challenge for quantum information science is to realize large-scale, precisely controllable, practical systems for multiparty secure communications. Recently, Guidry etal. [Nat. Photonics16, 52 (2022)10.1038/s41566-021-00901-z] have investigated the quantum optics of a Kerr-based optical frequency comb (OFC), which lays out the way for OFC acting as a quantum resource to realize a low-cost and stable multiparty continuous-variable quantum information processing. In this work, we propose a distributed quantum anonymous voting (DQAV) protocol based on discrete modulated coherent states, in which a Kerr-based OFC serves as the resource to generate multi-frequency quantum signals for multiparty voting. We consider both the single-selection and multiple-selection ballot scenarios, and design the phase compensation method for the OFC-based protocol. Voting security is ensured by the basic laws of quantum mechanics, while voting anonymity is achieved by the random assignment of different frequency sources and the homogeneity of the quantum operations taken on the same voting choice. Numerical analysis calculates the secure voting distance over the thermal-lossy channel, showing the advancement of the proposed protocol under multiparty and multivalued voting tasks.

Indoor channel modeling for continuous variable quantum key distribution in the terahertz band.

Continuous-variable quantum key distribution (CVQKD) in an indoor scenario can provide secure wireless access for practical short-distance communications with high rates. However, a suitable channel model for implementing the indoor CVQKD system has not been considered before. Here, we establish an indoor channel model to show the feasibility of CVQKD in terahertz (THz) band. We adopt both active and passive state preparation schemes to demonstrate the performance of the indoor CVQKD system involving multi-path propagation. We achieve the channel transmittance characterized by frequency, water-vapor density, antenna gain, reflection loss and the surrounding itself. The ray-tracing based numerical simulations show that the multi-path propagation can degrade the performance of the indoor CVQKD system. The maximum transmission distance is two meters at 410 GHz for both active and passive state preparations, and it can be extended to 35 and 20 meters respectively by using high gain antenna to combat the multi-path propagation.

Optical frequency comb-based multichannel parallel continuous-variable quantum key distribution.

Continuous-variable quantum key distribution (CVQKD) provides an approach for secure communication in optical fiber communication systems. However, its practical implementation has been hindered by low secret key bit rates that are usually limited to several bits/s to hundreds of kbits/s at distances of more than 25 kilometers. In this paper, we use a pair of optical frequency combs (OFCs) for both multiple parallel transmission and coherent reception, which assign multiple sub-channels involving multiple independent secret keys in a single fiber to increase the key bit rate. The first and last sub-channels are selected for propagating phase references to compensate the phase offset between two free-running combs. We analyze possible excess noise caused by dispersive walk-off in the transmission, imperfect phase compensation in the reception and photon leakage from the phase references. Compared to the previous single-channel CVQKD method, simulation results show more than a factor of 20 increase in the secret key rate at a transmission distance of 35 km and the number of comb lines of 35.