Practical repeaters for ultralong-distance quantum communication

Abstract

Quantum repeaters enable long-range quantum communication in the presence of attenuation. Here we propose a method to construct a robust quantum repeater network using only existing technology. We combine the ideas of brokered graph-state construction with double-heralded entanglement generation to form a system that is able to perform all parts of the procedure in a way that is highly tolerant to photon loss and imperfections in detectors. We show that when used in quantum key distribution this leads to secure kilohertz bit rates over intercontinental distances.

Quantum Networks with Deterministic Spin–Photon Interfaces

“…These include fast optical routing, efficient single-photon detectors, and the suppression of the general noise level to the 0.1% level for one-way repeaters [70,96,98] and to the 1% level for two-way repeaters. [64,66,71] Furthermore, high-performance entangling gate operations between emitters and conversion of optical signals to telecom wavelengths have to be developed. Nonetheless, it seems that solid-state emitters are already at a level of maturity where proof-of-principle experiments of the elementary building blocks discussed in this work may be realized in the near future.…”

“…Notably, this also opens up the possibility of performing both entanglement purification and entanglement swapping within the same diamond in a minimum resource setup (see Figure a). Having access to more than a single NV system will, however, allow the repeater to boost its rate through parallel entanglement generation attempts . The possibility to perform Bell measurements on different NV systems will also allow for multiplexed schemes, which can lower the memory time requirements …”

“…Since the first idea of a quantum repeater was presented, [64] numerous proposals for how to realize such devices have been formulated. [60,[65][66][67][68][69][70][71] The underlying structure of a quantum repeater has also been subject to investigation, resulting in proposals for repeater structures fundamentally different from the original one. In general, two classes of repeaters have been considered: two-way and one-way repeaters.…”

“…The required error levels are usually at the 1% level. [64,66,71] The entanglement generation and the memory aspect of the two-way repeater pose a number of challenges for solid-state emitters. The creation of high-quality entanglement by photon interference requires indistinguishable photons from different emitters.…”

A tunable waveguide-coupled cavity design for scalable interfaces to solid-state quantum emitters

“…The cavity fine-tuning, as proposed here using NEMS actuation, is required to tune and maintain many high-Q on-chip cavities on resonance for the realization of on-chip quantum networks and entanglement distribution in envisioned quantum repeater architectures. 45 Finally, this hybrid cavity design is compatible with the scalable hybrid assembly of a photonic backbone populated with pre-selected quantum nodes. 32,[46][47][48] The proposed approach requires careful alignment between the diamond and AlN components.…”