Superconducting Single-photon Detectors Research Articles

Matrix of Integrated Superconducting Single-Photon Detectors With High Timing Resolution

We demonstrate a large grid of individually addressable superconducting single photon detectors on a single chip. Each detector element is fully integrated into an independent waveguide circuit with custom functionality at telecom wavelengths. High device density is achieved by fabricating the nanowire detectors in traveling wave geometry directly on top of silicon-on-insulator waveguides. Our superconducting single-photon detector matrix includes detector designs optimized for high detection efficiency, low dark count rate and high timing accuracy. As an example, we exploit the high timing resolution of a particularly short nanowire design to resolve individual photon round-trips in a cavity ring-down measurement of a silicon ring resonator.

Full Numerical Simulations of Dynamical Response in Superconducting Single-Photon Detectors

We numerically study transport phenomena in a superconducting detector. Our approach is to simulate the three-dimensional time-dependent Ginzburg-Landau equation coupled with heat-diffusion and Maxwell equations. The simulation shows dynamical transition to a resistive state when an incident particle has energy higher than superconducting transition temperature. We show temporal behaviors of a superconducting gap function, depending on the incident energy scale. Furthermore, we discuss the applicability of our method to a superconducting single-photon detector. Focusing on the effects of coupling with heat sink and magnitude of quasi-particle fluctuations, we show a significant decrease of detector's threshold energy.

Universal response curve for nanowire superconducting single-photon detectors

Using detector tomography, we investigate the detection mechanism in NbN-based superconducting single photon detectors (SSPDs). We demonstrate that the detection probability uniquely depends on a particular linear combination of bias current and energy, for a large variation of bias currents, input energies and detection probabilities, producing a universal detection curve. We obtain this result by studying multiphoton excitations in a nanodetector with a sparsity-based tomographic method that allows factoring out of the optical absorption. We discuss the implication of our model system for the understanding of meander-type SSPDs.

Optical time domain reflectometry with low noise waveguide-coupled superconducting nanowire single-photon detectors

We demonstrate optical time domain reflectometry over 200 km of optical fiber using low-noise NbTiN superconducting single-photon detectors integrated with Si3N4 waveguides. Our small detector footprint enables high timing resolution of 50 ps and a dark count rate of 3 Hz with unshielded fibers, allowing for identification of defects along the fiber over a dynamic range of 37.4 dB. Photons scattered and reflected back from the fiber under test can be detected in free-running mode without showing dead zones or other impairments often encountered in semiconductor photon-counting optical time domain reflectometers.

Characteristics of superconducting single photon detector in DPS-QKD system under bright illumination blinding attack

We derive the time-dependent photo-detection probability equation of a superconducting single photon detector (SSPD) to study the responsive property for a pulse train at high repetition rate. Using this equation, we analyze the characteristics of SSPDs when illuminated by bright pulses in blinding attack on a quantum key distribution (QKD). We obtain good agreement between expected values based on our equation and actual experimental values. Such a time-dependent probability analysis contributes to security analysis.

Preparing Ultrathin MgB<sub>2</sub> Thin Film by <i>Ex Situ</i> Annealing of Mg-B Precursor Film

Ultrathin MgB2 film is essential for the fabrication of MgB2 superconducting single photon detectors (SSPDs). In this paper, we prepared 20nm and 10nm MgB2 film using ex-situ annealing of Mg-B multilayer method. The precursor films were prepared by electron beam evaporation. A flowing Mg vapour and H2 was introduced in the annealing process to keep MgB2 thin film thermodynamically stable. The annealing temperature was between 680 and 740 and annealing time was 1-10min. 20nm MgB2 films on MgO(111) substrates had the critical temperature (Tc) of 32.2K. The films grew along c-axes direction. As the substrate changed to SiC(001) and Al2O3(001), Tc decreased to 30.3K and 10.2K respectively. For 10nm MgB2 film on SiC(001) substrate, Tc was 24.2K. The self-field critical current density for 10nm and 20nm film on SiC(001) substrate was 2.1×106A/cm2 and 2.3×106A/cm2, respectively. AFM image showed that the film had a flat surface with mean roughness of 0.899nm for 10nm MgB2 film.

Superconducting detector dynamics studied by quantum pump-probe spectroscopy

We explore the dynamics of superconducting single-photon detectors (SSPDs) on the picosecond time-scale using a correlated photon-pair source based on spontaneous parametric downconversion (SPDC), corresponding to a pump-probe experiment at the single-photon level. We show that the detector can operate in a regime where the two-photon detection probability is orders of magnitude larger than the single-photon detection probability. The characteristic relaxation time-scale of the out-of-equilibrium hot-spot is found to be ∼15 ps. Our measurement technique is an effective tool to study fast two-photon processes, without requiring a power-dependence measurements to determine the number of photons involved.

Low-jitter single flux quantum signal readout from superconducting single photon detector

We developed a single-flux-quantum (SFQ) readout technology for superconducting single-photon detectors (SSPDs) to achieve low-jitter signal readout. By optimizing circuit parameters of the SFQ readout circuit, the input current sensitivity was improved below 10 μA, which is smaller than a typical critical current of SSPD. The experiment using a pulse-pattern generator as an input pulse source revealed that the measured jitter of the SFQ readout circuit is well below the system jitter of our measurement setup for the input current level above 15 μA. The measured jitter of the SSPD connected to the SFQ readout circuit was 37 ps full width at half maximum (FWHM) for an SSPD bias current of around 18 μA, which is a significant improvement on 67 ps FWHM jitter observed in conventional readout without an SFQ readout circuit.

Loophole-Free Bell Test Based on Local Precertification of Photon’s Presence

A loophole-free violation of Bell inequalities is of fundamental importance for demonstrating quantum nonlocality and long-distance device-independent secure communication. However, transmission losses represent a fundamental limitation for photonic loophole-free Bell tests. A local precertification of the presence of the photons immediately before the local measurements may solve this problem. We show that local precertification is feasible by integrating three current technologies: (i) enhanced single-photon down-conversion to locally create a flag photon, (ii) nanowire-based superconducting single-photon detectors for a fast flag detection, and (iii) superconducting transition-edge sensors to close the detection loophole. We carry out a precise space-time analysis of the proposed scheme, showing its viability and feasibility.

Timing performance of 30-nm-wide superconducting nanowire avalanche photodetectors

We investigated the timing jitter of superconducting nanowire avalanche photodetectors (SNAPs, also referred to as cascade-switching superconducting single-photon detectors) based on 30-nm-wide nanowires. At bias currents (IB) near the switching current, SNAPs showed sub-35-ps FWHM Gaussian jitter similar to standard 100-nm-wide superconducting nanowire single-photon detectors. At lower values of IB, the instrument response function (IRF) of the detectors became wider, more asymmetric, and shifted to longer time delays. We could reproduce the experimentally observed IRF time-shift in simulations based on an electrothermal model and explain the effect with a simple physical picture.

Large area single photon detectors based on parallel configuration NbN nanowires

The authors present superconducting single photon detectors (SSPDs) based on parallel nanostrips with an area up to 40 × 40 μm2. The SSPDs presented here are based on 100 nm wide ultrathin NbN nanostrips with a filling factor of 40%. The devices are fabricated by extending the standard electron beam lithography (EBL) patterning process to those densely structured large areas. By a thorough characterization it is shown that the electrical properties of the parallel SSPDs are comparable with those of smaller devices, as expected, proving in this way that the extended EBL process results in uniform nanostrips also in large area detectors. Furthermore, the estimated maximum count rate of the 40 × 40 μm2 parallel SSPDs was 33 MHz, showing that the parallel nanostrip configuration is much faster when compared with standard meandered serial SSPDs. The successful extension of parallel SSPDs to a large area coverage opens a new route to the use of such detectors also with multimode fibers.

2 GHz clock quantum key distribution over 260 km of standard telecom fiber

We report a demonstration of quantum key distribution (QKD) over a standard telecom fiber exceeding 50 dB in loss and 250 km in length. The differential phase shift QKD protocol was chosen and implemented with a 2 GHz system clock rate. By careful optimization of the 1 bit delayed Faraday-Michelson interferometer and the use of the superconducting single photon detector (SSPD), we achieved a quantum bit error rate below 2% when the fiber length was no more than 205 km, and of 3.45% for a 260 km fiber with 52.9 dB loss. We also improved the quantum efficiency of SSPD to obtain a high key rate for 50 km length.

Requirements on Photon Counting Detectors for Terahertz Interferometry

Future Terahertz astronomy requires higher angular resolution observations. One possibility is to use photon counting interferometry, which is similar to the intensity interferometry demonstrated by Hanbury Brown and Twiss in 1956. In terahertz frequencies, it will be possible to measure all the photon arrivals and can identify bunched photons from thermal sources to measure correlation amplitude and time delay of the photon arrivals. By obtaining the complex visibility, aperture synthesis images can be obtained. I name this technology as photon counting terahertz interferometry (PCTI). From scientific case study, requirements to the detectors are high photon counting rate and accurate time resolution. I discuss on requirements on possible detector technologies such as superconducting single photon detectors (SSPD), superconducting tunnel junction (STJ) detectors and charge sensitive infrared photo-transistors (CSIP).

Tantalum nitride superconducting single-photon detectors with low cut-off energy

Materials with a small superconducting energy gap are expected to favor a high detection efficiency of low-energy photons in superconducting nanowire single-photon detectors. We developed a TaN detector with smaller gap and lower density of states at the Fermi energy than in comparable NbN devices, while other relevant parameters remain essentially unchanged. The observed reduction of the minimum photon energy required for direct detection is in line with model predictions of ≈1/3 as compared to NbN.

Response properties of NbN superconductor nanowire for multi-photon

In this paper, we study the response properties of multi-photon of NbN superconductor nanowire in superconducting single photon detector (SSPD). We measure the NbN nanowire device's DC characteristics and detection probability for single and multi-photon light pulse signal at a temperature of 3.5 K. The measured results show that the superconducting transition current of superconductor nanowire decreases as light irradiation intensity increases. The photon number detected by SSPD is derived from the slope of detection probability versus light intensity. We find that the detected photon number increases as superconducting nanowire bias current decreases. Moreover, based on quantum optics and hotspot theory, we analyze the mechanism of the multi-photon response of superconducting nanowire semi-quantitatively. This result may be of benefit to understanding SSPD and developing the SSPD with the capability of resolving photon number.

NbN Superconducting Single-Photon Detector with Bilayer Structure

We fabricated a superconducting single-photon detector (SSPD) with bilayer structure. The detector consists of two meanders which are superposed face-to-face using optical adhesive. When the two nanowires are superposed perpendicularly, the degree of linear polarization dependence is reduced from 0.16 to 0.000617. This means that the polarization dependence, which has been a drawback in SSPDs, is suppressed almost completely using the present structure.

NbN Nanowire Superconducting Single-Photon Detector for Mid-Infrared

Abstract Superconducting single-photon detectors (SSPD) is typically 100 nm-wide supercondiucting strip in a shape of meander made of 4-nm-thick film. To reduce response time and increase voltage response a parallel connection of the strips was proposed. Recently we demonstrated that reduction of the strip width improves the quantum effciency of such a detector at wavelengths longer than 1.5 μm. Being encourage by this progress in quantum effciency we improved the fabrication process and made parallel-wire SSPD with 40-nm-wide strips covering total area of 10 μm x 10 μm. In this paper we present the results of the characterization of such a parallel-wire SSPD at 10.6 μm wavelength and demonstrate linear dependence of the count rate on the light power as it should be in case of single-photon response.

Direct numerical simulation for non-equilibrium transport phenomena in superconducting detectors

We numerically study non-equilibrium transport phenomena in a superconducting detector using the time-dependent Ginzburg-Landau equation coupled with the heat diusion and Maxwell equations. The simulation showsadynamical transition from the superconducting to the resistive states via incident particle's energy higher than kBTc. We also discuss the applicability of our method to a superconducting single-photon detector.

Waveguide superconducting single-photon detectors for integrated quantum photonic circuits

The monolithic integration of single-photon sources, passive optical circuits, and single-photon detectors enables complex and scalable quantum photonic integrated circuits, for application in linear-optics quantum computing and quantum communications. Here, we demonstrate a key component of such a circuit, a waveguide single-photon detector. Our detectors, based on superconducting nanowires on GaAs ridge waveguides, provide high efficiency (∼20%) at telecom wavelengths, high timing accuracy (∼60 ps), and response time in the ns range and are fully compatible with the integration of single-photon sources, passive networks, and modulators.

Afterpulse-like phenomenon of superconducting single photon detector in high speed quantum key distribution system

We discuss our estimates of the performance of a superconducting single photon detector (SSPD) in a high speed quantum key distribution (QKD) system. We find that at high repetition operation reflections from the readout circuit at room temperature causes an afterpulse-like phenomenon, and drastically increases the quantum bit error rate (QBER). Such effects are not seen during low frequency operation. By using an amplifier with a small reflection coefficient S11, we succeed in reducing the afterpulse-like phenomenon and increasing a secure key rate.