Waveguide integrated superconducting single-photon detectors implemented as near-perfect absorbers of coherent radiation.

At the core of an ideal single-photon detector is an active material that absorbs and converts every incident photon to a discriminable signal. A large active material favours efficient absorption, but often at the expense of conversion efficiency, noise, speed and timing accuracy. In this work, short (8.5 µm long) and narrow (8 × 35 nm(2)) U-shaped NbTiN nanowires atop silicon-on-insulator waveguides are embedded in asymmetric nanobeam cavities that render them as near-perfect absorbers despite their small volume. At 2.05 K, when biased at 0.9 of the critical current, the resulting superconducting single-photon detectors achieve a near-unity on-chip quantum efficiency for ∼1,545 nm photons, an intrinsic dark count rate <0.1 Hz, a reset time of ∼7 ns, and a timing jitter of ∼55 ps full-width at half-maximum. Such ultracompact, high-performance detectors are essential for progress in integrated quantum optics.

Reduced dark counts in optimized geometries for superconducting nanowire single photon detectors.

We have experimentally compared the critical current, dark count rate and photo-response of 100nm wide superconducting nanowires with different bend designs. Enhanced critical current for nanowires with optimally rounded bends, and thus with no current crowding, are observed. Furthermore, we find that the optimally designed bend significantly reduces the dark counts without compromising the photo-response of the device. The results can lead to major improvements in superconducting nanowire single photon detectors.

Gated mode superconducting nanowire single photon detectors.

Single Photon Detectors are fundamental to quantum optics and quantum information. Superconducting nanowire detectors exhibit high performance in free-running mode, but have a limited maximum count rate. By exploiting a bistable superconducting nanowire system, we demonstrate the first gated-mode operation of these detectors for a large active area single element device at 625MHz, one order of magnitude faster than its free-running counterpart. We show the maximum count rate in gated-mode operation can be pushed to GHz range without a compromise on the active area or quantum efficiency, while reducing the dark count rate.

Nonlinearity in single photon detection: modeling and quantum tomography.

Single Photon Detectors are integral to quantum optics and quantum information. Superconducting Nanowire based detectors exhibit new levels of performance, but have no accepted quantum optical model that is valid for multiple input photons. By performing Detector Tomography, we improve the recently proposed model [M.K. Akhlaghi and A.H. Majedi, IEEE Trans. Appl. Supercond. 19, 361 (2009)] and also investigate the manner in which these detectors respond nonlinearly to light, a valuable feature for some applications. We develop a device independent model for Single Photon Detectors that incorporates this nonlinearity.