Design and analysis of communication protocols for quantum repeater networks

Abstract

We analyze how the performance of a quantum-repeater network depends on the protocol employed to distribute entanglement, and we find that the choice of repeater-to-repeater link protocol has a profound impact on entanglement-distribution rate as a function of hardware parameters. We develop numerical simulations of quantum networks using different protocols, where the repeater hardware is modeled in terms of key performance parameters, such as photon generation rate and collection efficiency. These parameters are motivated by recent experimental demonstrations in quantum dots, trapped ions, and nitrogen-vacancy centers in diamond. We find that a quantum-dot repeater with the newest protocol ('MidpointSource') delivers the highest entanglement-distribution rate for typical cases where there is low probability of establishing entanglement per transmission, and in some cases the rate is orders of magnitude higher than other schemes. Our simulation tools can be used to evaluate communication protocols as part of designing a large-scale quantum network. succinctly, managing photon loss is crucial for designing quantum networks, and the interference and detection of two single-photon signals enables reliable determination of whether a signal was received or lost in transmission while also being more robust to path-length fluctuations than single-detection schemes [28,48].The paper begins with some preliminary considerations for distributing entanglement in section 2. Section 3 examines three protocols for establishing entanglement between repeaters, and we simulate the performance of these protocols in section 4 using hardware parameters representative of recent experimental work. Section 5 summarizes our results and discusses related communication schemes that we chose not to examine, though they are appropriate for future work. PreliminariesWe begin by listing a few features common to any of the repeaters we consider. As shown in figure 1, each repeater has some number of controllable memory qubits that must have long coherence times (of order 10 ms) and low-error gates to act on these memory qubits (error per gate below 0.1%). The memory qubits may be protected with error correction [16,[24][25][26][27] to extend their coherence time or suppress gate error. Furthermore, there is an interface for generating an entangled state between a memory qubit and a single-photonic qubit. We will simply say photon to mean a photonic qubit, since there is no ambiguity in this paper. For example, memory/photon entangled states have been demonstrated for ions, NV centers in diamond, and quantum dots [29,36,37,39,[41][42][43]49]. The memory/photon entanglement is a resource for generating entanglement between repeaters, by swapping entanglement using the photons (described below).Each quantum repeater in a network has multiple optical links to its neighbors. In this paper, we focus on protocols for efficiently distributing entanglement across the link between two repeaters. As in figure 1, each repeater will devote some of its memo...

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