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As a competitive technology, the superconducting nanowire single-photon detector (SNSPD) is developing from a single-pixel to array architecture; however, it is a major challenge for reading array detectors. We propose an encodable trigger through the thermal coupling of two adjacent superconducting nanowires, which can read a current pulse with microampere amplitude and code the current pulses of different positions with different output resistances simultaneously. At the same time, the influence of external noise on superconducting devices can be avoided for isolated circuits. As a demonstration, the response pulses of a 4-pixel SNSPD are read using this trigger in the absence of an amplifier, and the photon flux distribution of different pixels is accurately reconstructed, where the total power consumption is approximately 0.8 μW. The superconducting trigger is promising for application in integrated superconducting electronics and quantum optics in the future.

In this Letter, we report on pattern engineering in superconducting microstrips to achieve a fast and efficient detection of a single-photon over a large detection area. The proposed detector is composed of hole-patterned superconductor microstrips fabricated with a 5-nm-thick amorphous molybdenum silicide film. It exhibits a saturated internal detection efficiency at 1550 nm with a negligible dark count rate and a recovery time of 9 ns with a large detection area (50 × 50 μm2). The simulation reveals that the holes patterned in the superconductor microstrip stimulate the nucleation of the vortex, which constitutes a major key to achieving the efficient detection of photons. This work paves the way for the facile and prolonged regulation of vortex nucleation in superconductors, which shows promise for developing high-performance large-area superconductor single-photon detectors.

In this Letter, we report on a device with which to resolve photon numbers and positions simultaneously, using single-channel readout from superconducting nanowire single-photon detectors (SNSPDs). The nanowires in the SNSPDs are connected in series with parallel resistors for producing response pulses with different amplitudes, whose values obey a distribution of 1:2:4:,..,2n-1. In single-photon detection, a saturated counting rate is obtained at a low dark count rate (

Terahertz (THz) photonic waveguides are of great importance in THz integrated technology, especially for versatile signal processing. However, in THz photonics, very few fundamental “building blocks” equivalent to those used in muti-functional electronics circuits exist. This study proposes a photonics-inspired micro-ring whispering gallery mode resonator (WGMR) waveguide with a standard waveguide-compatible package on silicon platform. A gradual taper is integrated on the same chip to improve the coupling efficiency and reduce transmission loss. The packaged WGMR waveguide with an operating range of 0.360 to 0.440 THz had a maximum measured extinction ratio of 32 dB at 0.390 THz, with a Q factor of 385 and an insertion loss of 2.6 dB. The compact and standard waveguide-compatible packaged WGMR can easily be integrated into practical terahertz application systems for THz signal processing and as a tool for the study of fundamental THz science.

We demonstrate in this paper the tunable electromagnetically induced transparency (EIT) made from a superconducting (SC) niobium nitride (NbN) film induced by an intense terahertz (THz) field. As the variation of the incident THz field alters the intrinsic ohmic loss of the SC NbN film, the field-dependent transmittance is observed. To elaborate the role of the bright and dark modes, a hybrid coupling model is introduced to fit the experimental transmission spectra and extract the characteristic parameters of each mode. It is shown that the resonator for the bright mode is altered greatly due to strong direct coupling to the incident intense THz field, whereas the dark mode resonator has little interaction with the incident THz field via a weak near-filed coupling to the bright-mode resonator. This implies that we can partially control a mode or a part of metamaterial by introducing the intense THz field, which offers an effective manner to selectively control the electromagnetic property of the metamater...

We demonstrate that the subradiant mode in ultrathin bi-layer metamaterials can be exclusively excited under two-antisymmetric-beam illumination (or equivalently, at a node of the standing wave field), while the superradiant mode is fully suppressed due to their different mode symmetry. Coherent perfect absorption (CPA) with the Lorentzian lineshape can be achieved corresponding to the subradiant mode. A theoretical model is established to distinguish the different behaviors of these two modes and to elucidate the CPA condition. Terahertz ultrathin bi-layer metamaterials on flexible polyimide substrates are fabricated and tested, exhibiting excellent agreement with theoretical predictions. This work provides physical insight into how to selectively excite the antisymmetric subradiant mode via coherence incidence.

We investigate the vortex ratchet effects in a superconducting asymmetric ring-shaped NbN device. Through transport measurements, we find that the rectified dc voltages are significantly enhanced, and we observe time-dependent asymmetric voltage waveforms over a single cycle. Our vortex ratchet device operates over a wide range of temperatures, critical currents, and magnetic fields. We demonstrate that in this asymmetric structure giant ratchet effects are mainly caused by the collective behavior of vortices, which differs clearly from one-particle vortex effects studied in conventional vortex ratchet systems.

This paper studies the suppression of superconducting transition temperature (T(c)) of ultrathin NbN film. We fabricated epitaxial NbN superconducting thin films of thicknesses ranging from 2.5 to 100 nm on single crystal MgO (100) substrates by dc magnetron sputtering. We performed structure analyses and measured their electric and far infrared properties. The experimental results were compared with several mechanisms of the suppression of superconductivity proposed in the literature, including the weak localization effect, the proximity effect, and quantum size effect (electron wave leakage model). We found that the electron wave leakage model matches best to the experimental data. (C) 2011 American Institute of Physics. [doi:10.1063/1.3518037]