A High-Efficiency Broadband Superconducting Nanowire Single-Photon Detector with a Composite Optical Structure

Superconducting nanowire single-photon detectors （SNSPDs） with a composite optical structure composed of phase-grating and optical cavity structures are designed to enhance both the system detection efficiency and the response bandwidth. Numerical simulation by the finite-difference time-domain method shows that the photon absorption capacity of SNSPDs with a composite optical structure can be enhanced significantly by adjusting the parameters of the phase-grating and optical cavity structures at multiple frequency bands. The absorption capacity of the superconducting nanowires reaches 70%, 72%, 60.73%, 61.7%, 41.2%, and 46.5% at wavelengths of 684, 850, 732, 924, 1256, and 1426nm, respectively. The use of a composite optical structure reduces the total filling factor of superconducting nanowires to only 0.25, decreases the kinetic inductance of SNSPDs, and improves the count rates.

Wavelength dependence of intrinsic detection efficiency of NbN superconducting nanowire single-photon detector

Superconducting nanowire single-photon detectors(SNSPDs) have attracted considerable attention owing to their excellent detection performance;however, the underlying physics of the detection process is still unclear.In this study, we investigate the wavelength dependence of the intrinsic detection efficiency(IDE) for NbN SNSPDs.We fabricate various NbN SNSPDs with linewidths ranging from 30 nm to 140 nm.Then, for each detector, the IDE curves as a function of bias current for different incident photon wavelengths of 510–1700 nm are obtained.From the IDE curves, the relations between photon energy and bias current at a certain IDE are extracted.The results exhibit clear nonlinear energy–current relations for the NbN detectors, indicating that a detection model only considering quasiparticle diffusion is unsuitable for the meander-type NbN-based SNSPDs.Our work provides additional experimental data on SNSPD detection mechanism and may serve as an interesting reference for further investigation.

High-performance eight-channel system with fractal superconducting nanowire single-photon detectors

Superconducting nanowire single-photon detectors(SNSPDs)have become a mainstream photon-counting technology that has been widely applied in various scenarios.So far,most multi-channel SNSPD systems,either reported in literature or commercially available,are polarization sensitive,that is,the system detection efficiency(SDE)of each channel is dependent on the state of polarization of the to-be-detected photons.Here,we reported an eight-channel system with fractal SNSPDs working in the wavelength range of 930 to 940 nm,which are all featured with low polarization sensitivity.In a close-cycled Gifford-McMahon cryocooler system with the base temperature of 2.2 K,we installed and compared the performance of two types of devices:(1)SNSPD,composed of a single,continuous nanowire and(2)superconducting nanowire avalanche photodetector(SNAP),composed of 16 cascaded units of two nanowires electrically connected in parallel.The highest SDE among the eight channels reaches 96+^(4)_(-5%),with the polarization sensitivity of 1.02 and a dark-count rate of 13 counts per second.The average SDE for eight channels for all states of polarization is estimated to be 90±5%.It is concluded that both the SNSPDs and the SNAPs can reach saturated,high SDE at the wavelength of interest,and the SNSPDs show lower dark-count(false-count)rates,whereas the SNAPs show better properties in the time domain.With the adoption of this system,we showcased the measurements of the second-order photon-correlation functions of light emission from a singlephoton source based on a semiconductor quantum dot and from a pulsed laser.It is believed that this work will provide new choices of systems with single-photon detectors combining the merits of high SDE,low polarization sensitivity,and low noise that can be tailored for different applications.

Photon-Counting Spectrometers Based on Superconducting Nanowire Single-Photon Detectors

Optical spectrum analysis provides a wealth of information about the physical world.Throughout the development of optical spectrum analysis,sensitivity has been one of the major topics and has become essential in applications dealing with faint light.Various high-sensitivity optical detection technologies have been applied in optical spectrum analysis to enhance its sensitivity to single-photon level.As an emerging single-photon detection technology,superconducting nanowire single-photon detectors(SNSPDs)have many impressive features such as high detection efficiency,broad operation bandwidth,small timing jitter,and so on,which make them promising for enhancing the performance of optical spectral analysis.Diverse schemes for photon-counting spectrometers based on SNSPDs have been demonstrated.This article reviews these impressive works and prospects for the future development of this technology.Further breakthroughs can be expected in its theories,device performance,applications,and combinations with in-sensor computing,promoting it to be a mature and versatile solution for optical spectrum analysis on ultra-faint light.

Large-inductance superconducting microstrip photon detector enabling 10 photon-number resolution

Efficient and precise photon-number-resolving detectors are essential for optical quantum information science.Despite this,very few detectors have been able to distinguish photon numbers with both high fidelity and a large dynamic range,all while maintaining high speed and high timing precision.Superconducting nanostrip-based detectors excel at counting single photons efficiently and rapidly,but face challenges in balancing dynamic range and fidelity.Here,we have pioneered the demonstration of 10 true photon-number resolution using a superconducting microstrip detector,with readout fidelity reaching an impressive 98%and 90%for 4-photon and 6-photon events,respectively.Furthermore,our proposed dual-channel timing setup drastically reduces the amount of data acquisition by 3 orders of magnitude,allowing for real-time photon-number readout.We then demonstrate the utility of our scheme by implementing a quantum random-number generator based on sampling the parity of a coherent state,which guarantees inherent unbiasedness,robustness against experimental imperfections and environmental noise,as well as invulnerability to eavesdropping.Our solution boasts high fidelity,a large dynamic range,and real-time characterization for photon-number resolution and simplicity with respect to device structure,fabrication,and readout,which may provide a promising avenue towards optical quantum information science.

Dual-lens beam compression for optical coupling in superconducting nanowire single-photon detectors

The optical coupling of superconducting nanowire single-photon detectors （SNSPDs） has always been restricted to a single-mode fiber for a limited detection area. In this study, for enhancing photon coupling, a dual-lens system operating at 2.2 K was used to compress the beam size on the basis of the Gaussian beam theory and geometric approximation. A magnification of approximately 0.3 was obtained, and a focused spot with diameter of approximately 10 ~m was measured from a multimode fiber. Assisted with the compressed beam, a system efficiency of 55 % （1550 nm） was achieved for a SNSPD with a detection area of 10 μm × 10 μm and 62.5 pm multimode fiber coupling. At the same time, a high speed of 106 MHz was measured with the proposed system. The realization of a highly compressed optical beam reduced the optical coupling requirement and helped maintain a high speed for the SNSPD.

Superconducting single-photon detectors integrated with diamond nanophotonic circuits

Photonic quantum technologies hold promise to repeat the success of integrated nanophotonic circuits in non-classical applications.Using linear optical elements,quantum optical computations can be performed with integrated optical circuits and can therefore overcome the existing limitations in terms of scalability.In addition to passive optical devices for realizing photonic quantum gates,active elements,such as single-photon sources and single-photon detectors,are essential ingredients for future optical quantum circuits.Material systems that allow for the monolithic integration of all components are particularly attractive,including III-V semiconductors,silicon and diamond.Here,we demonstrate nanophotonic integrated circuits made from high-quality polycrystalline diamond thin films in combination with on-chip single-photon detectors.By using superconducting nanowires that are coupled evanescently to traveling waves,we achieve high detection efficiencies of up to 66%as well as low dark count rates and a timing resolution of 190 ps.Our devices are fully scalable and hold promise for functional diamond photonic quantum devices.

Wideband cryogenic amplifier for a superconducting nanowire single-photon detector

We present a low-power inductorless wideband differential cryogenic amplifier using a 0.13-μm Si Ge Bi CMOS process for a superconducting nanowire single-photon detector(SNSPD).With a shunt-shunt feedback and capacitive coupling structure,theoretical analysis and simulations were undertaken,highlighting the relationship of the amplifier gain with the tunable design parameters of the circuit.In this way,the design and optimization flexibility can be increased,and a required gain can be achieved even without an accurate cryogenic device model.To realize a flat terminal impedance over the frequency of interest,an RC shunt compensation structure was employed,improving the amplifier’s closed-loop stability and suppressing the amplifier overshoot.The S-parameters and transient performance were measured at room temperature(300 K)and cryogenic temperature(4.2 K).With good input and output matching,the measurement results showed that the amplifier achieved a 21-d B gain with a 3-d B bandwidth of 1.13 GHz at 300 K.At 4.2 K,the gain of the amplifier can be tuned from 15 to 24 d B,achieving a 3-d B bandwidth spanning from 120 k Hz to 1.3 GHz and consuming only 3.1 m W.Excluding the chip pads,the amplifier chip core area was only about 0.073 mm^(2).

Superconducting nanowire single-photon detectors:recent progress

Research of superconducting nanowire singlephoton detectors(SNSPDs) has been progressing rapidly in recent years. The combined properties of high efficiency,low noise, and fast speed of SNSPDs permit its applications ranging from long-distance quantum teleportation to moonto-earth optical communications. Here we briefly discussed recent progress of SNSPDs, in particular(1) tungstensilicide SNSPDs,(2) waveguide-integrated SNSPDs, and(3) a few applied demonstrations.

Geometric origin of intrinsic dark counts in superconducting nanowire single-photon detectors

The dark count is one of the key physical issues for superconducting nanowire single-photon detectors(SNSPDs)that limits various applications for optical quantum information and classical optics.When the bias current approaches the switching current of SNSPDs,the dark count is actually dominated by the intrinsic dark counts(iDCs).However,the origin of iDCs and its relation to constrictions remains unclear for practical SNSPDs.We herein systematically characterize the iDCs of the SNSPDs with and without artificial geometric constrictions by applying the differential readout method.For these devices with constrictions,we have observed distinct Gaussian distributions in the temporal distribution of iDCs,in which the time difference between the distributions is consistent with the geometric distance between constrictions,and the rates of iDCs produced by each constriction are in good agreement with constrictions'widths.With respect to practical SNSPDs,surprisingly,we also observe several Gaussian distributions in the temporal domain and it shows no significant dependence on the devices’sizes,demonstrating that the iDCs of SNSPDs are mainly dominated by a few specific constrictions.

NbN superconducting nanowire single photon detector with efficiency over 90% at 1550 nm wavelength operational at compact cryocooler temperature

The rapid development of superconducting nanowire single-photon detectors over the past decade has led to numerous advances in quantum information technology. The record for the best system detection efficiency at an incident photon wavelength of 1550 nm is 93%. This performance was attained from a superconducting nanowire single-photon detector made of amorphous WSi; such detectors are usually operated at sub-Kelvin temperatures. In this study, we first demonstrate superconducting nanowire single-photon detectors made of polycrystalline NbN with system detection efficiency of 90.2% for 1550-nm-wavelength photons at2.1 K, accessible with a compact cryocooler. The system detection efficiency saturated at 92.1% when the temperature was lowered to 1.8 K. We expect the results lighten the practical and high performance superconducting nanowire single-photon detectors to quantum information and other high-end applications.

Superconducting nanostrip single photon detectors fabricated of aluminum thin-films

We systematically investigated the detection performance of Al nanostrips for single photons at various wavelengths.The Al films were deposited using magnetron sputtering,and the sophisticated nanostructures and morphology of the deposited films were revealed through high-resolution transmission electron microscopy.The fabricated Al meander nanostrips,with a thickness of 4.2 nm and a width of 178 nm,exhibited a superconducting transition temperature of 2.4 K and a critical current of approximately 5μA at 0.85 K.While the Al nanostrips demonstrated a saturated internal quantum efficiency for 405-nm photons,the internal detection efficiency exhibited an exponential dependence on bias current without any saturation tendency for 1550-nm photons.This behavior can be attributed to the relatively large diffusion coefficient and coherence length of the Al films.By further narrowing the nanostrip width,the Al-SNSPDs remain capable of effectively detecting single telecom photons to facilitate practical applications.

SNSPD二十年:回顾与展望

21世纪初,GOL’TSMAN等人开启了超导纳米线单光子探测器(SNSPD)这一研究领域。历经整整20年的发展,SNSPD已经成为综合性能优异的单光子探测器,被广泛用于量子与经典的弱光探测。本文从性能指标、器件物理、薄膜材料、器件结构、加工工艺、光学耦合、信号读出、制冷系统、应用演示等9个方面,回顾了过去20年里SNSPD的重要研究进展;在此基础上,展望和评述了未来可能的研究与发展方向。