Ultrafast, high-efficiency single-photon detectors are among the most sought-after elements in modern quantum optics and quantum communication. However, imperfect modal matching and finite photon ...absorption rates have usually limited their maximum attainable detection efficiency. Here we demonstrate superconducting nanowire detectors atop nanophotonic waveguides, which enable a drastic increase of the absorption length for incoming photons. This allows us to achieve high on-chip single-photon detection efficiency up to 91% at telecom wavelengths, repeatable across several fabricated chips. We also observe remarkably low dark count rates without significant compromise of the on-chip detection efficiency. The detectors are fully embedded in scalable silicon photonic circuits and provide ultrashort timing jitter of 18 ps. Exploiting this high temporal resolution, we demonstrate ballistic photon transport in silicon ring resonators. Our direct implementation of a high-performance single-photon detector on chip overcomes a major barrier in integrated quantum photonics.
We present our studies on the evolution of the normal and superconducting properties with thickness of thin Nb films with a low level of non-magnetic disorder (<inline-formula><tex-math ...notation="LaTeX">k_Fl\approx 150</tex-math></inline-formula> for the thickest film in the set). The analysis of the superconducting behavior points to the presence of magnetic moments, hidden in the native oxide on the surface of Nb films. Using the Abrikosov-Gorkov theory, we obtain the density of surface magnetic moments of <inline-formula><tex-math notation="LaTeX">10^{13}</tex-math></inline-formula> cm<inline-formula><tex-math notation="LaTeX">^{-2}</tex-math></inline-formula>, which is in agreement with the previously reported data for Nb films.
Abstract
The experimental and numerical study both generation and transmission terahertz pulse in a nonlinear crystal partially filling the rectangular metallic waveguide cross-section is presented. ...LiNbO
3
and DAST crystals have been studied since they have a high-quality factor (FOM) and optical rectification in them is the most promising method for generating an extremely strong terahertz field. Experimentally and numerically has been shown that, depending on the thickness and permittivity of a nonlinear crystal, a broadband terahertz pulse can propagate with low absorption in the form of the fundamental H
10
mode or a linear superposition of H
no
modes.
Radio-frequency modulated terahertz (THz) emission power from weakly-coupled GaAs/AlGaAs superlattice (SL) has been increased by parallel connection of several SL mesas. Each SL mesa is a ...self-oscillator with its own oscillation frequency and mode. In coupled non-identical SL mesas biased at different voltages within the hysteresis loop the chaotic, quasiperiodic and frequency-locked modes of self-oscillations of current arise. THz emission was detected when three connected in parallel SL mesas were biased into the frequency-locked and quasiperiodic modes of self-oscillations of current, while in the chaotic mode of those it falls to the noise level.
We put forward two methods for phase stabilization in the all-fiber Michelson interferometer. To perform passive phase stabilization, we use a heat bath for all fibers and electro-optical components, ...and put the interferometer in a hermetic case. To perform active phase stabilization, we monitor output power of the interferometer and develop an electronic feedback control. The phase stabilization methods enable stable interference pattern for several minutes, and can be helpful for the development of the optimal quantum receiver for coherent signals.
Practical implementation of high-precision quantum measurements is an important problem in modern science. One of the main parts of the quantum receiver is the optical scheme. We developed and tested ...several optical circuits based on different types of interferometers, namely Sagnac-based scheme, Mach-Zehnder-based scheme, and Michelson-based scheme. All these schemes are assembled with optical fibers and fiber-optic components, since the fiber-optic implementation is closest to application in practical devices. Schemes were evaluated according to two main criteria: extinction and interference stability. On the basis of the obtained data, it can be concluded that the most suitable is the scheme based on the Mach-Zehnder interferometer. In continuous mode, we were able to obtain an interference extinction about 30 dB with acceptable temporal stability.
Here, we report on the successful operation of a NbN thin film superconducting nanowire single-photon detector (SNSPD) in a coherent mode (as a mixer) at the telecommunication wavelength of 1550 nm. ...Providing the local oscillator power of the order of a few picowatts, we were practically able to reach the quantum noise limited sensitivity. The intermediate frequency gain bandwidth (also referred to as response or conversion bandwidth) was limited by the spectral band of a single-photon response pulse of the detector, which is proportional to the detector size. We observed a gain bandwidth of 65 MHz and 140 MHz for 7 × 7 µm
and 3 × 3 µm
devices, respectively. A tiny amount of the required local oscillator power and wide gain and noise bandwidths, along with unnecessary low noise amplification, make this technology prominent for various applications, with the possibility for future development of a photon counting heterodyne-born large-scale array.
We experimentally demonstrate strong temperature dependence of the critical current of the superconducting 600-nm-wide and 5-μm-long bridge made of NbN/Au bilayer. The result is achieved due to the ...proximity effect realized between the highly disordered superconducting NbN layer and low resistive normal-metal Au layer.
PDF
