Quasi-1-Dimensional Superconductivity in Highly Disordered NbN Nanowires
Further development of quantum emitter based communication and sensing applications intrinsically depends on the availability of robust single-photon detectors. Here, we demonstrate a new generation of superconducting single-photon detectors specifically optimized for the 500-1100 nm wavelength range, which overlaps with the emission spectrum of many interesting solid-state atom-like systems, such as nitrogen-vacancy and silicon-vacancy centers in diamond. The fabricated detectors have a wide dynamic range (up to 350 million counts per second), low dark count rate (down to 0.1 counts per second), excellent jitter (62 ps), and the possibility of on-chip integration with a quantum emitter. In addition to performance characterization, we tested the detectors in real experimental conditions involving nanodiamond nitrogen-vacancy emitters enhanced by a hyperbolic metamaterial.
A specific property of a planar tunnel junction with thin-film diffusive plates and long enough leads, typical for most of practical situations, is essential enhancement of its transmission coefficient compared to the bare transparency of the tunnel barrier [1,2]. In voltage-biased junctions, this creates favorable conditions for strong nonequilibrium of quasiparticles in the junction plates and leads, produced by multiparticle tunneling. We study theoretically the interplay between the nonequilibrium and relaxation processes in such junctions and found that nonequilibrium in the leads noticeably modifies the current-voltage characteristic at eV>2Δ , especially the excess current, whereas strong diffusive relaxation restores the result of the classical tunnel model. At eV≤2Δ , diffusive relaxation decreases the peaks of the multiparticle currents. Inelastic relaxation in the junction plates essentially suppresses the n -particle currents (n>2 ) by the factor n for odd and n/2 for even n . The results may be important for the problem of decoherence in Josephson-junction based superconducting qubits.
Traditional photon detectors are operated in direct detection mode, counting incident photons with a known quantum efficiency. Here we have investigated a Superconducting-Nanowire-Single-Photon-Detector (SNSPD) operated as a photon counting mixer at telecommunication wavelength around 1.5 micrometers. This regime of operation combines the excellent sensitivity of a photon counting detector with the excellent spectral resolution given by the heterodyne technique. Advantageously, we have found that low LO power of the order of hundreds of femtowatts to a few picowatts is sufficient for clear observation of the incident test signal with the sensitivity approaching the quantum limit. With further optimization, the required LO power could be significantly reduced, which is promising for many practical applications, such as development of receiver matrices or recording ultra-low signals at a level of less-than-one-photon per second.
In addition to a traditional NbN-based SNSPD operated with normal incidence coupling, we also use detectors with a travelling wave geometry, where a NbN nanowire is placed on the top of a Si3N4 nanophotonic waveguide. This approach is fully scalable and a large number of devices could be integrated on a single chip.
The development of terahertz imaging instruments for security systems is on the cutting edge of terahertz technology. We are developing a THz imaging system based on a superconducting integrated receiver (SIR). An SIR is a new type of heterodyne receiver based on an SIS mixer integrated with a flux-flow oscillator (FFO) and a harmonic mixer which is used for phase-locking the FFO. Employing an SIR in an imaging system means building an entirely new instrument with many advantages compared to traditional systems. In this project we propose a prototype THz imaging system using an 1 pixel SIR and 2D scanner. At a local oscillator frequency of 500 GHz the best noise equivalent temperature difference (NETD) of the SIR is 10 mK at an integration time of 1 s and a detection bandwidth of 4 GHz. The scanner consists of two rotating flat mirrors placed in front of the antenna consisting of a spherical primary reflector and an aspherical secondary reflector. The diameter of the primary reflector is 0.3 m. The operating frequency of the imaging system is 600 GHz, the frame rate is 0.1 FPS, the scanning area is 0.5 × 0.5 m2, the image resolution is 50 × 50 pixels, the distance from an object to the scanner was 3 m. We have obtained THz images with a spatial resolution of 8 mm and a NETD of less than 2 K.
The problem of designing stabilizing resonator (SR) for a 4-mm wavelengths range coaxial magnetron with low level of output power has been considered. The recommendations for choosen the coaxial resonator external to internal diameter relations depending on technical project requirements are developed.
This volume presents new results in the study and optimization of information transmission models in telecommunication networks using different approaches, mainly based on theiries of queueing systems and queueing networks .
The paper provides a number of proposed draft operational guidelines for technology measurement and includes a number of tentative technology definitions to be used for statistical purposes, principles for identification and classification of potentially growing technology areas, suggestions on the survey strategies and indicators. These are the key components of an internationally harmonized framework for collecting and interpreting technology data that would need to be further developed through a broader consultation process. A summary of definitions of technology already available in OECD manuals and the stocktaking results are provided in the Annex section.