Superconducting Single-Photon Detectors for GHz-Rate Free-Space Quantum Communications

摘要

We report our studies on the performance of new NbN ultrathin-film superconducting single-photon detectors (SSPDs). Our SSPDs exhibit experimentally measured quantum efficiencies from ～5% at wavelength λ = 1550 nm up to ～10% at λ = 405 nm, with exponential, activation-energy-type spectral sensitivity dependence in the 0.4-μm - 3-μm wavelength range. Using a variable optical delay setup, we have shown that our NbN SSPDs can resolve optical photons with a counting rate up to 10 GHz, presently limited by the read-out electronics. The measured device jitter was below 35 ps under optimum biasing conditions. The extremely high photon counting rate, together with relatively high (especially for λ > 1 μm) quantum efficiency, low jitter, and very low dark counts, make NbN SSPDs very promising for free-space communications and quantum cryptography.