Superconducting nanowire single photon detectors (SNSPDs) have emerged as a leading choice for high performance single photon detectors due to their low timing jitter, high detection efficiency, and low dark count rates. SNSPDs have typically been biased using a passive quenching scheme in which the bias current of the device is shunted through a resistive load to allow for recovery after a detection event. To prevent latching, the shunting resistor must be approximately an order of magnitude smaller than the peak normal domain resistance of the SNSPD. Consequentially, the pulse amplitude (∝IBRL) and recovery time (∝LK/RL) are both negatively impacted. In this talk, we will describe a novel approach to the bias and read-out of SNSPDs based upon active quenching. We will present detailed design considerations for an active quenching architecture and will show that such an approach has the potential to improve count rates while increasing signal swings to the point where external amplification is no longer required. A silicon germanium (SiGe) active-reset chip design has been designed, implemented, and integrated with a NbTiN SNSPD. The procedure for the SiGe chip design will be described and simulation results will be presented. Finally, detailed measurement results of the complete system will be shown and compared to measurements of the same detector when biased and read-out using a standard passive quenching scheme. It will be shown that the active quenching configuration enables a considerable enhancement to the system performance.
Superconducting nanowire single photon detectors (SNSPDs) have emerged as a leading choice for high performance single photon detectors due to their low timing jitter, high detection efficiency, and low dark count rates. SNSPDs have typically been biased using a passive quenching scheme in which the bias current of the device is shunted through a resistive load to allow for recovery after a detection event. To prevent latching, the shunting resistor must be approximately an order of magnitude smaller than the peak normal domain resistance of the SNSPD. Consequentially, the pulse amplitude (∝IBRL) and recovery time (∝LK/RL) are both negatively impacted. In this talk, we will describe a novel approach to the bias and read-out of SNSPDs based upon active quenching. We will present detailed design considerations for an active quenching architecture and will show that such an approach has the potential to improve count rates while increasing signal swings to the point where external amplification is no longer required. A silicon germanium (SiGe) active-reset chip design has been designed, implemented, and integrated with a NbTiN SNSPD. The procedure for the SiGe chip design will be described and simulation results will be presented. Finally, detailed measurement results of the complete system will be shown and compared to measurements of the same detector when biased and read-out using a standard passive quenching scheme. It will be shown that the active quenching configuration enables a considerable enhancement to the system performance.
Superconducting nanowire single photon detectors are typically biased using a constant current source and shunted in a conductance that is over an order of magnitude larger than the peak normal domain conductance of the detector. While this design choice is required to ensure quenching of the normal domain, the use of a small load resistor limits the pulse amplitude, rising-edge slew rate, and recovery time of the detector. Here, we explore the possibility of actively quenching the normal domain, thereby removing the need to shunt the detector in a small resistance. We first consider the theoretical performance of an actively quenched superconducting nanowire single photon detector and, in comparison to a passively quenched device, we predict roughly an order of magnitude improvement in the slew rate and peak voltage achieved in this configuration. The experimental performance of actively and passively quenched superconducting nanowire single photon detectors are then compared. It is shown that, in comparison to a passively quenched device, the actively quenched detectors simultaneously exhibited improved count rates, dark count rates, and timing jitter.
Superconducting nanowire single-photon detectors (SNSPDs) are an attractive technology for applications which benefit from high-count rate photon detection such as quantum communication protocols, photon-starved classical communications, metrology of single-emitters, and photonic quantum computing. However, at high-count rates, a significant portion of photons may be incident during recovery intervals following prior detection events. After detection, the device efficiency recovers over nanoseconds to tens of nanoseconds before reaching a steadystate value. Therefore, for a given SNSPD bias current setpoint, a single efficiency and recovery time specification may not be sufficient to characterize the performance of a device at high count rates. Here we present and experimentally validate a model of the recovery time as a function of bias current for any given system efficiency. These results may be used to improve analysis of measurements performed using SNSPDs operating in the high count rate regime.
Superconducting nanowire single photon detector (SNSPD) has been widely used in many fields such as quantum computing, quantum key distribution and laser radar, due to its high detection efficiency, low dark count rate, high counting rate, and low timing jitter. In most cases, the SNSPD works under the DC-bias mode that can detect single photons arrived at any time. In some cases such as satellite laser ranging and single-photon laser radar where the light pulses arrive regularly, the AC-bias mode enables the SNSPD to work with higher counting rates and lower background dark counts, which however requires complicated readout due to the low signal-to-noise ratio of the photon response. In this work, we report on an AC-biased SNSPD system with a self-differential readout circuit. The system includes a 2-pixel SNSPD consisting of two parallel nanowires, which are biased with 100 MHz sinusoidal current. The output signals of these two nanowires are amplified and combined for the differential readout of the photon response. The resulting response pulse possesses a signal-to-noise ratio ten times higher than that extracted before self-differential readout. In addition, the dark counts are reduced by a factor of 4, and the count rates are increased by a factor of 1.5, in comparison with those under the DC-bias mode. This work provides a specific method to read out the AC-biased SNSPD.
Superconducting nanowire single-photon detectors (SNSPDs), owing to their unique performance, are currently the standard detector in most demanding single-photon experiments. One important metric for any single-photon detector is the recovery time, which defines the minimum temporal separation between consecutive detection events. In SNSPDs, the recovery time is more subtle, as the detection efficiency does not abruptly drop to zero when the temporal separation between detection events gets smaller, instead, it increases gradually as the SNSPD current recovers. SNSPD's recovery time is dominated by its kinetic inductance, the readout impedance, and the degree of saturation of internal efficiency. Decreasing the kinetic inductance or increasing the readout impedance can accelerate the recovery process. Significant reduction of the SNSPD recovery time, by, for example, adding a series resistor in the readout circuitry, is possible but can lead to detector latching, which hinders further detector operation or enforces underbiasing and hence a reduction in detection efficiency. Previous research has demonstrated passive resistive networks for the reduction of recovery time that rely on trial and error to find the appropriate resistance values. Here, we show that, using a cryogenically compatible and tunable resistor technology, one can find the optimized impedance values, delivering fast SNSPD recovery time while maintaining maximum internal detection efficiency. Here, we show an increase of around twofold in both maximum achievable detection rates and the achievable detection efficiency at high photon fluxes, demonstrating detection rates close to 114 Mcps with no loss of internal detection efficiency.
In recent years, Superconducting Nanowire Single-Photon Detectors (SNSPDs) have obtained tremendous attention as a possible key technology for photonic quantum processing and faint light detection. Here, we present our recent progress on engineering of the properties of NbTiN SNSPDs fabricated on various substrates measured. We discuss approaches to simultaneously improve the most important figures of merit (DCR, dead time, timing jitter, efficiency) as well as efficient characterization methods. Specifically, for the latter we investigate the impact of the substrate material on the performance parameters as well as the fundamental interrelation of the resulting voltage pulse properties, such as pulse height, rise time and timing jitter, and their dependence on the applied bias current.
Ever since superconducting nanowire single-photon detectors (SNSPDs or SSPDs) were demonstrated, they have attracted a considerable attention due to the detectors’ promising performance that includes high detection efficiency (DE), low dark count rate (DCR), broadband sensitivity, and low timing jitter. The system detection efficiency (SDE) has been improved to be over 90% with a wavelength of 1550 nm in a fiber-coupled system by embedding the SNSPD in optical cavities. However, the implementation of optical cavity usually reduces the bandwidth of SNSPDs. As a result, there are some recent works on increasing the bandwidth of SNSPD. Furthermore, the size of the active area of meandered nanowires has to be compatible with the core size of an optical fiber such that good optical coupling can be achieved; this setup requires a long nanowire with a large kinetic inductance, thus resulting in a small counting rate and a large timing jitter, particularly for multi-mode fiber-coupled devices. Nevertheless, a particularly impressive waveguide-coupled SNSPD has been developed in recent years. By placing an SNSPD atop an optical waveguide that has been fabricated on various substrate materials, photons propagating in the waveguide have been found to be evanescently absorbed by nanowires that are only a few tens of microns long. The on-chip DE of this device has been estimated to be over 90%, thus indicating that it has both high absorptance and high intrinsic DE. If the waveguide and the nanowire are correctly dimensioned, the absorptance of this device can reach over 90% for a wavelength range of more than 700 nm. Furthermore, the length of the nanowire is shorter than that of the fiber-coupled SNSPD, thus leading to a higher count rate and lower timing jitter (~18 ps). However, unsatisfactory coupling losses between the optical fiber and the waveguide in such devices can decrease its SDE (~10%), thus limiting its applicability to quantum photonic integrated circuits (QPIC). Recently, we proposed a type of SNSPD that was coupled with microfibers (MFs), and simulations for this SNSPD indicated that its absorption would be as high as 90%. Microfibers and nanofibers, tapered adiabatically from standard fibers, with diameters close to or smaller than the wavelength of the guided light were demonstrated to have low transmittance losses by Tong et al. in 2003. MFs have been shown to have many interesting properties, such as strong evanescent fields, tight optical confinement, wideband abilities, and small masses; these properties are appealing for applications such as optical sensing and coupling. MFs also provide seamless connections with high transmittance from standard fibers; therefore, MF-coupled SNSPDs can achieve both high SDEs and wideband compatibility. We proposed and demonstrated the MF-coupled SNSPDs successfully. The simulation results indicate that with optimal device structure, the optical absorption with efficiency < 90% can be realized over a wavelength range of 350 nm to 2150 nm. The fabricated MF-coupled SNSPD, shows unparalleled broadband system detection efficiencies (SDEs) of more than 50% from 630 nm to 1500 nm. The SDEs reach 66% at 785 nm and 45% at 1550 nm. These results pave the way for ultra-broadband weak light detection with quantum-limit sensitivity.