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 have remained elusive. We present a novel 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.
Highlights
A quantum internet [1] that distributes entanglement and quantum-secure shared secret keys at high rates over large distances exemplifies the goal of quantum communications [2]
Our results demonstrate that the proposed quantum repeater scheme for continuous variables (CVs) entanglement distribution in principle works and beats direct transmission
It is important to emphasize that the entanglement source repetition rate of Rrep = 1 MHz was chosen as such to ensure that the corresponding requirements on the multimode quantum memories used at the repeater nodes are met under current technologies
Summary
A quantum internet [1] that distributes entanglement and quantum-secure shared secret keys at high rates over large distances exemplifies the goal of quantum communications [2]. Though the limiting case is unphysical, it carries semblance to DV repeaters, where entanglement distillation is typically based on the successful detection of photons arriving at a repeater node, such that a successful detection event heralds a perfect ebit of entanglement and the detection success probability scales proportional to the transmissivity of the repeater link This prompts us to consider switched multiplexing over multiple modes (spectral, temporal, spatial, or a combination of any of these) between each pair of adjacent nodes in the proposed CV repeater scheme similar to the so-called second generation DV repeater schemes [17], where mode multiplexing was shown to enable the end-to-end per-mode rates to beat direct transmission [18,41].
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