Recently, a new generation of hot-electron superconducting sensors: terahertz mixers, direct detectors and single-photon counters have been developed.These sensors have already demonstrated a performance that makes them devices-of-choice for many terahertz and optical applications.

The superconducting hot electron bolometer(HEB) mixers based on ultrathin films of NbN combine the best sensitivity at the frequencies well above 1 THz and a gain bandwidth of about 5-6 GHz which make them suitable for most sensitive instruments being developed in the far IR region for astronomical and atmospheric studies.

Direct detectors made from NbN and MoRe films are operated in 0.3-3 THz range exhibit response time as low as 50 ps and 1 ns respectively with noise equivalent power (NEP) of 3x10‑13 W Hz-1/2(NbN) and 5x10-14 W Hz-1/2(MoRe). Another versions of these detectors have a broadband sensitivity in 0.1-30 THz range with the same response time and exhibit higher NEP but much higher dynamic range. A promising type of the photon counting detector is superconducting single-photon detector (SSPD). The SSPD is patterned from 4-nm-thick NbN film as 120-nm-wide and meander-shaped strip that covers a square area of 10 x 10 μm2. At wavelength λ≤1.3 μm quantum efficiency (QE) of our best devices approaches 30% at 2 K with 35 ps timing jitter. The single-photon counting was observed at wavelength up to 5.6 μm with QE of ~1%. Simultaneously, at 2K the SSPD has negligibly low dark counts of 2x10‑4 s‑1. It provides NEP value of 10-20 W/Hz1/2 at λ≤1.3 μm and 10-18 W/Hz1/2 at 5 µm. Our recent investigations allowed us to develop an SSPD with photon-number resolving capability. Single-, two-, three- and four-photon absorptions were clearly observed. Finally, successful coupling of the SSPD with a single mode optical fiber makes SSPD a device of choice for wide range of applications including study of single-photon sources, telecom systems, quantum key distribution systems and quantum computing.

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1. Ultrafast Superconducting Single-Photon Detectors for Near-Infrared-Wavelength Quantum Communications