Continuous-variable quantum repeater based on quantum scissors and mode multiplexing

Abstract

Quantum repeaters are indispensable for high-rate, long-distance quantum communications. The vision of a future quantum internet strongly hinges on realizing quantum repeaters in practice. Numerous repeaters have been proposed for discrete-variable (DV) single-photon-based quantum communications. Continuous-variable (CV) encodings over the quadrature degrees of freedom of the electromagnetic field mode offer an attractive alternative. For example, CV transmission systems are easier to integrate with existing optical telecom systems compared to their DV counterparts. Yet, repeaters for CV quantum communications have remained elusive. We present a quantum repeater scheme for CV entanglement distribution over a lossy bosonic channel that beats the direct transmission exponential rate-loss tradeoff. The scheme involves repeater nodes consisting of (a) two-mode squeezed vacuum (TMSV) CV entanglement sources; (b) the quantum scissors operation to perform nondeterministic noiseless linear amplification of lossy TMSV states; (c) a layer of switched mode multiplexing inspired by second-generation DV repeaters, which is the key ingredient apart from probabilistic entanglement purification that makes DV repeaters work; and (d) a non-Gaussian entanglement swap operation. We report our exact results on the rate-loss envelope achieved by the scheme.