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Quantum teleportation is one of the fundamental primitives of quantum cryptography. In order to achieve a wider range of high-capacity information transfer, we propose a free-space quantum teleportation (QT) protocol with orbital angular momentum (OAM) multiplexed continuous variable (CV) entangled states. The preparation of the entangled states is accomplished by the spontaneous four-wave mixing (SFWM) process occurring in a hot 85 Rb vapor cell, and the mode selection for the Bell-state measurement is achieved by employing the balanced homodyne detection technique. The fidelity of teleporting EPR entangled states carrying different topological charges via a Kolmogorov-type atmospheric turbulence channel is derived, and the superiority of enhancing the system channel capacity via OAM multiplexing is demonstrated. Our work provides a feasible scheme to implement high-capacity quantum communication in atmospheric environments. [ABSTRACT FROM AUTHOR]

Frequency entangled state originated from optical frequency comb (OFC) is an important quantum source for quantum communication. In this paper, we propose a traveling quantum anonymous voting (TQAV) protocol, which employs a monolithic microresonator with cascaded four-wave mixing (FWM) to prepare continuous-variable frequency entanglement sources. Multi-pair EPR entangled states and five-partite entangled states generated from the degenerate and nondegenerate FWM process are used as signal sources for the TQAV to characterize different candidates. Voters are able to vote for their preferred candidates by performing displacement operations on the received modes, and the ballot agency can judge the voting result according to the measurements. The entanglement property of the quantum state is utilized to keep voters away from the voting results. The security of the protocol under collective attacks and spectroscopic noise attacks is guaranteed by the security mechanism of continuous-variable quantum key distribution. Our results provide a reference for the application of OFC in multiparty quantum communication. [ABSTRACT FROM AUTHOR]

In satellite-to-submarine quantum communication, sea surface, which may cause refraction and propagation light deflection, is a non-negligible obstacle. These negative effects can result in severe performance decrease. In this paper, we carry out satellite-to-submarine quantum communication by taking advantage of the principle of measurement-device-independent continuous-variable quantum key distribution (MDI-CVQKD). In particular, by deploying the untrusted party Charlie on the sea surface, the satellite-to-submarine quantum channel can be divided into two parts, namely the atmospheric channel and the seawater channel. Quantum signals no longer need to pass through the sea surface, but can be directly measured at Charlie's station. In this way, negative effects caused by the sea surface can be tactfully eliminated. Security analysis shows that our proposed scheme is feasible, thereby providing a novel thought to implement satellite-to-submarine quantum communication. [ABSTRACT FROM AUTHOR]

We propose a new scheme to strengthen the performance of the discrete-modulated continuous-variable measurement-device-independent quantum key distribution (DM-CV-MDI-QKD) protocol by introducing a quantum scissors (QS) operation to Bob's side. According to the equivalent one-way scheme of the protocol, we further investigate the success probability of the QS operation, and analyze the security of the DM-CV-MDI-QKD equipped with this operation in the asymptotic case. Simulation results show that the QS operation can indeed effectively improve the performance of the existing protocol, and compared with the scheme without QS operation, our proposed scheme has a higher secret key rate and a longer secure transmission distance. [ABSTRACT FROM AUTHOR]

The secret key rate is one of the main obstacles to the practical application of continuous-variable quantum key distribution (CVQKD). In this paper, we propose a multiplexing scheme to increase the secret key rate of the CVQKD system with orbital angular momentum (OAM). The propagation characteristics of a typical vortex beam, involving the Laguerre–Gaussian (LG) beam, are analyzed in an atmospheric channel for the Kolmogorov turbulence model. Discrete modulation is utilized to extend the maximal transmission distance. We show the effect of the transmittance of the beam over the turbulent channel on the secret key rate and the transmission distance. Numerical simulations indicate that the OAM multiplexing scheme can improve the performance of the CVQKD system and hence has potential use for practical high-rate quantum communications. [ABSTRACT FROM AUTHOR]

Numerous continuous-variable quantum key distribution (CV-QKD) schemes are based on the Gaussian modulation, which is carried out in conjugate quadratures. In order to simplify the traditional protocols, as well as improving the security of the system, we propose the plug-and-play unidimensional CV-QKD protocol, which waives the necessity of propagating a local oscillator (LO) between legitimate users and generates a real local LO for quantum measurement. The new protocol utilizes only one phase modulator rather than two, which is different from the dual-phase-modulated coherent-states protocol that we proposed earlier. The prepare-and-measure and entanglement-based schemes are described. The security of the new protocol against collective attacks in a Gaussian channel is analyzed, and the security boundary is derived, which is achieved by establishing the relationship between the uncertain parameters of the unmodulated quadrature. The performance of it is analyzed in both asymptotic and finite-size cases. Such an efficient scheme not only provides a way of removing the security loopholes associated with the transmitting LO, but also eliminates the need for one of the phase modulators, and thus will facilitate commercialization of continuous-variable quantum key distribution. [ABSTRACT FROM AUTHOR]