Abstract
AbstractElementary building blocks for quantum repeaters based on fiber channels and memory stations are analyzed. Implementations are considered for three different physical platforms, for which suitable components are available: quantum dots, trapped atoms and ions, and color centers in diamond. The performances of basic quantum repeater links for these platforms are evaluated and compared, both for present‐day, state‐of‐the‐art experimental parameters as well as for parameters that can in principle be reached in the future. The ultimate goal is to experimentally explore regimes at intermediate distances—up to a few 100 km—in which the repeater‐assisted secret key transmission rates exceed the maximal rate achievable via direct transmission. Two different protocols are considered, one of which is better adapted to the higher source clock rate and lower memory coherence time of the quantum dot platform, while the other circumvents the need of writing photonic quantum states into the memories in a heralded, nondestructive fashion. The elementary building blocks and protocols can be connected in a modular form to construct a quantum repeater system that is potentially scalable to large distances.
Highlights
Quantum key distribution (QKD) and related schemes are offering a paradigm change in establishing secure communication: algorithmic security is replaced by physically secure generation of encryption keys.[1]
As the effective clock rate in a memory-based QKD or quantum repeaters (QRs) system is always slower than that of a direct point-to-point quantum connection driven from a laser source at ∼GHz rates, the memorybased system will become potentially more efficient only at large
A necessary requirement for a large-scale QR to show a performance superior to that of direct transmission is that its fundamental elements already exceed the bounds constraining a “repeaterless” system on a smaller scale: employing an elementary QR cell or a two-segment QR should on average lead to a larger secret key or qubit transmission rate than obtainable in a direct transmission
Summary
Quantum correlations from two entangled point-to-point segments AA′ and B′B are connected via a collective Bell-state measurement (BM) at the central “repeater” node A′B′, resulting in so-called entanglement swapping to nodes A and B (Figure 2) These larger segments can be concatenated further in the same way, while a simple multiplication of the channel transmission efficiencies per segment and a propagation and accumulation of errors can be prevented by storing quantum information in quantum memories and applying entanglement purification on many entangled pairs in each segment[21] or incorporating quantum error correction codes into the memory qubits.[20] Overcoming the distance and rate limitations in a scalable fashion, QRs offer highly attractive functionality for future long-range quantum networks.[22]. Let us first introduce a minimal set of experimental parameters that can be used to quantitatively assess the performance of a memory-based QR system
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