Superconducting Nanowire Single-photon Detectors Research Articles

High-speed low-crosstalk detection of a 171Yb+ qubit using superconducting nanowire single photon detectors

Qubits used in quantum computing suffer from errors, either from the qubit interacting with the environment, or from imperfect quantum logic gates. Effective quantum error correcting codes require a high fidelity readout of ancilla qubits from which the error syndrome can be determined without affecting data qubits. Here, we present a detection scheme for 171Yb+ qubits, where we use superconducting nanowire single photon detectors and utilize photon time-of-arrival statistics to improve the fidelity and speed. Qubit shuttling allows for creating a separate detection region where an ancilla qubit can be measured without disrupting a data qubit. We achieve an average qubit state detection time of 11 μs with a fidelity of 99.931(6). The detection crosstalk error, defined as the probability that the data qubit coherence is lost due to the process of detecting an ancilla qubit, is reduced to ~2 × 10−5 by creating a separation of 370 μm between them.

Utilizing niobium plasmonic perfect absorbers for tunable near- and mid-IR photodetection.

With the fast development of single photon-based technologies such as quantum computing and quantum cryptography, conventional avalanche photodiodes as single photon detectors are not the optimum tools anymore. They are currently replaced by Superconducting Nanowire Single Photon Detectors (SNSPDs) based on the superconducting to normal conducting phase transition. The current challenge with SNSPDs lies in overcoming the trade-off between detection efficiency and recovery time. While a large active area will lead to high detection efficiency, the associated high kinetic inductance causes a long recovery time. Plasmonic effects can play an important role in the absorption enhancement of SNSPDs. Nanostructuring with a suitable geometry can provide a high-absorption cross-section at the intrinsic nanowire surface plasmon resonance, which can be significantly larger than their geometric cross-section. We present a photodetector based on the intrinsic localized surface plasmon resonance of a niobium nanowire, which is one of the common superconductors with low kinetic inductance. Additionally, we are increasing the absorption of our nanostructures even further using a plasmonic perfect absorber scheme. We fabricated a plasmonic perfect absorber superconducting photodetector, investigated its response to external light at resonance, and proved its plasmonic behavior as evidenced by its polarization dependence.

Superconducting nanowire single photon detectors operating at temperature from 4 to 7 K.

We experimentally investigate the performance of NbTiN superconducting nanowire single photon detectors above the base temperature of a conventional Gifford-McMahon cryocooler (2.5 K). By tailoring design and thickness (8 - 13 nm) of the detectors, high performance, high operating temperature, single-photon detection from the visible to telecom wavelengths are demonstrated. At 4.3 K, a detection efficiency of 82 % at 785 nm wavelength and a timing jitter of 30 ± 0.3 ps are achieved. In addition, for 1550 nm and similar operating temperature we measured a detection efficiency as high as 64 %. Finally, we show that at temperatures up to 7 K, unity internal efficiency is maintained for the visible spectrum. Our work is particularly important to allow for the large scale implementation of superconducting single photon detectors in combination with heat sources such as free-space optical windows, cryogenic electronics, microwave sources and active optical components for complex quantum optical experiments and bio-imaging.

A Silicon Shallow-Ridge Waveguide Integrated Superconducting Nanowire Single Photon Detector Towards Quantum Photonic Circuits**Supported by the National Key R&D Program of China under Grant Nos 2017YFA0303704 and 2017YFA0304000, the National Natural Science Foundation of China under Grant Nos 61575102, 91750206, 61671438, 61875101 and 61621064, the Beijing Natural Science Foundation under Grant No Z180012, and the Beijing Academy of Quantum Information

A silicon shallow-ridge waveguide integrated superconducting nanowire single photon detector is designed and fabricated. At the bias current of 11.6 μA, 4% on-chip detection efficiency near 1550 nm wavelength is achieved with the dark count rate of 3 Hz and a timing jitter of 75 ps. This device shows the potential application in the integration of superconducting nanowire single photon detectors with a complex quantum photonic circuit.

Protocol of Measuring Hot-Spot Correlation Length for SNSPDs With Near-Unity Detection Efficiency

We present a simple quantum detector tomography protocol, which allows, without ambiguities, to measure the two-spot detection efficiency and extract the hot-spot interaction length of superconducting nanowire single photon detectors (SNSPDs) with unity intrinsic detection efficiency. We identify a significant parasitic contribution to the measured two-spot efficiency, related to an effect of the bias circuit, and find a way to rule out this contribution during data post-processing and directly in the experiment. From the data analysis for waveguide-integrated SNSPD, we find signatures of the saturation of the two-spot efficiency and hot-spot interaction length of order of 100 nm.

A Stochastic SPICE Model for Superconducting Nanowire Single Photon Detectors and Other Nanowire Devices.

Superconducting nanowire devices, such as the superconducting nanowire single photon detector (SNSPD) or nanocryotron, have a time-dependent stochasticity that depends on the current flowing through them. When modeling complex circuits made of several such devices (for instance, an array of SNSPDs), the ability to include this randomness can be important for predicting unwanted effects and interactions within the circuit. We present a modification of the model described by Berggren et al. that allows for the inclusion of this stochasticity into the nanowire device model. We then verify the model against experiment using a tungsten silicide SNSPD, and show that the modified model replicates the stochasticity of the physical device.

Timing Jitter Characterization of the SFQ Coincidence Circuit by Optically Time-Controlled Signals From SSPDs

We report on the timing jitter characterization of the superconducting single flux quantum (SFQ) coincidence circuit, which is an essential component of the superconducting coincidence photon counter. Two superconducting nanowire single photon detectors (SSPDs), each of which is irradiated with optically time-controlled photons, are connected to the SFQ coincidence circuit, and the timing jitter of the SFQ circuit is evaluated by changing the relative time delay between two input ports for the SFQ comparator unit. We successfully observe the transition curve of the probability of obtaining the signal from the SFQ coincidence circuit by sweeping photon arrival time to each SSPD and confirm that this curve shifts temporally upon changing the bias current to the Josephson transmission line (JTL) in the SFQ circuit. A systematic investigation reveals that the relation between time delay and the bias current to JTL can be estimated. The full width half maximum timing jitter of the SFQ circuit is 1.1 ps, which is sufficiently low so that it does not influence the entire timing jitter of the coincidence photon counter.

A 16-Pixel Interleaved Superconducting Nanowire Single-Photon Detector Array With A Maximum Count Rate Exceeding 1.5 GHz

Increasing the count rate (CR) is one of the key issues in the development of superconducting nanowire single-photon detectors (SNSPDs) for different applications. This study aims to design, fabricate, and analyze a 16-pixel interleaved nanowire SNSPD array, which exhibits a system detection efficiency (SDE) of 72% and a dark CR of 100 Hz at a low-photon-flux limit and a wavelength of 1550 nm. By exploiting the increased pixel number and reduced dead time (<;5 ns) of each nanowire, the SNSPD array attained a maximum CR of 1.5 GHz with an SDE of ~12% at a photon flux of 1.26 × 10 10 photons/s. Moreover, the SNSPD achieved a photon number resolution of up to 16 photons.

Low-Power Digital Readout Circuit for Superconductor Nanowire Single-Photon Detectors

We designed and tested the digital readout circuitry for superconducting nanowire single-photon detectors (SNSPDs). The designed time-to-digital converter (TDC) comprises a decision-making block, a clock controller, and a counter with parallel-to-serial (P2S) interface. We also designed an on-chip pattern generator to imitate a digitized SNSPD response that allowed us to screen the circuitry without bonding actual SNSPDs. Both rapid single-flux quantum (RSFQ) and its energy-efficient rapid single-flux quantum (ERSFQ) versions were designed for comparison and debugging purposes. To optimize the design of the feeding Josephson transmission line (FJTL) required by the ERSFQ variant, we compared different power grid structures and types of FJTLs. Using an 8-bit counter with P2S interface as a device under test, we also investigated the effect of FJTL's size on the bias margins. FJTL with a 75% junction overhead is sufficient for the ERSFQ circuit to match the margins of its RSFQ counterpart. All chips have been fabricated at MIT-LL using the SFQ5ee process node. Experimental results and future research directions are presented.

Enhancement of Optical Response in Nanowires by Negative-Tone PMMA Lithography

The method of negative-tone polymethyl methacrylate (PMMA) electron-beam lithography is investigated to improve the performance of nanowire-based superconducting detectors. Using this approach, the superconducting nanowire single-photon detectors (SNSPDs) have been fabricated from 5-nm-thick NbN film sputtered at room temperature. To investigate the impact of this process, SNSPDs were prepared by positive-tone- and negative-tone-PMMA lithography, and their electrical and photodetection characteristics at 4.2 K were compared. The SNSPDs made by negative-tone-PMMA lithography show higher critical-current density and higher photon count rate at various wavelengths. Our results suggest a higher negative-tone-PMMA technology may be preferable to the standard positive-tone-PMMA lithography for this application.

Geometrical Jitter and Bolometric Regime in Photon Detection by Straight Superconducting Nanowire

We present a direct observation of the geometrical jitter in single photon detection by a straight superconducting nanowire. Differential measurement technique was applied to the 180-μm long nanowire similar to those commonly used in the technology of superconducting nanowire single photon detectors (SNSPD). A non-Gaussian geometrical jitter appears as a wide almost uniform probability distribution (histogram) of the delay time (latency) of the nanowire response to detected photon. White electrical noise of the readout electronics causes broadened, Gaussian-shaped edges of the histogram. Subtracting noise contribution, we found for the geometrical jitter a standard deviation of ≈8.5 ps and the full width at half maximum (FWHM) of the distribution of ≈29 ps. FWHM corresponds to the propagation speed of the electrical signal along the nanowire of ≈6.2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> m/s or 0.02 of the speed of light. Alternatively the propagation speed was estimated from the central frequency of the measured first-order self-resonance of the nanowire. Both values agree well with each other and with previously reported values. As the intensity of the incident photon flux increases, the wide probability distribution collapses into a much narrower Gaussian distribution with a standard deviation dominated by the noise of electronics. We associate the collapse of the histogram with the transition from the discrete, single photon detection to the uniform bolometric regime.

Development of 2-K Space Cryocoolers for Cooling the Superconducting Nanowire Single Photon Detector

The superconducting nanowire single photon detector (SNSPD) plays an important role in quantum key distribution, satellite laser ranging, and space quantum communication, etc. The required temperature of around 2K poses a significant challenge for the suitable cryogenic system. Especially, when used in space, the emphasized high reliability, long operation life time, limited room, and power supply make the challenge more formidable. The pulse tube cryocooler (PTC) without any moving component at the cold end has the intrinsic merits of high reliability and long life time at the cold head, and the Stirling-type PTC (SPTC) driven by the linear compressor also achieves the long life time and reliability in the compressor, and thus the SPTC becomes an attractive candidate for cooling the SNSPD. To achieve the aimed 2K, two proposals based on the SPTC are investigated. One is the four-stage SPTC and the other the three-stage SPTC plus a J-T cooler. This paper presents the structural design and performance improvement of both proposals. The measured no-load temperatures of the four-stage SPTC and the three-stage SPTC/J-T are 4.38 and 5.68K, respectively. The final steps to obtain the simulated 2.1- and 1.6K, respectively, are underway.

Characterization of a Photon-Number Resolving SNSPD Using Poissonian and Sub-Poissonian Light

Photon-number resolving (PNR) single-photon detectors are of interest for a wide range of applications in the emerging field of photon-based quantum technologies. Especially photonic integrated circuits will pave the way for a high complexity and ease of use of quantum photonics. Superconducting nanowire singlephoton detectors (SNSPDs) are of special interest since they combine a high detection efficiency and a high timing accuracy with a high count rate and they can be configured as PNR-SNSPDs. Here, we present a PNR-SNSPD with a four photon resolution suitable for waveguide integration operating at a temperature of 4 K. A high statistical accuracy for the photon number is achieved for a Poissonian light source at a photon flux below 5 photons/pulse with a detection efficiency of 22.7 ± 3 % at 900 nm and a pulse rate frequency of 76 MHz. We demonstrate the ability of such a detector to discriminate a sub-Poissonian from a Poissonian light source.

Single-Flux-Quantum Based Event-Driven Encoder for Large-Pixel Superconducting Nanowire Single-Photon Detector Array

We propose a single-flux-quantum (SFQ) based event-driven encoder for a large-pixel superconducting nanowire single-photon detector (SSPD) array with a row-column readout architecture. The designed SFQ encoder can acquire time-tagged address data with a high time resolution. To apply 32 × 32 pixel SSPD system with a row-column architecture, the SFQ encoder is equipped with two 32-channel input ports among which one is for positive pulses, whereas the other is for negative pulses. The number of Josephson junctions (JJs) in the designed circuit is 2780. The power dissipation and required total bias current are 0.21 mW and 170 mA, respectively, owing to the reductions in critical currents of the JJs and bias resistors. The circuit generates time-tagged address data by applying electrical pulses at room temperature not only in liquid helium but also in a 0.1-W Gifford-McMahon (GM) cryocooler.

Jitter Characterization of a Dual-Readout SNSPD

To better understand the origins of the timing resolution, also known as jitter, of superconducting nanowire single-photon detectors (SNSPDs), we have performed timing characterizations of a niobium nitride SNSPD with a dual-ended readout. By simultaneously measuring both readout pulses along with an optical timing reference signal, we are able to quantify each independent contribution to the total measured jitter. In particular, we are able to determine values for the jitter due to the stochastic nature of hotspot formation and the jitter due to the variation of the photon detection location along the length of the nanowire. We compare the results of this analysis for measurements at temperatures of 1.5 K and 4.5 K.

Comparison of SNSPDs Biased With Microwave and Direct Currents

This paper presents a detailed investigation of superconducting nanowire single-photon detectors (SNSPDs) biased with microwave and direct currents. We developed a hybrid detector, which allows the operation in the rf and dc operation mode. With this hybrid detector, we are able to compare the count rates of the same nanowire biased with dc and rf currents. Furthermore, we demonstrate the use of the oscillating current in the rf operation mode as a reference signal in a synchronous single-photon detection mode.

Superconducting properties of tungsten nanowires fabricated using focussed ion beam technique

We report superconducting properties of tungsten meander structures fabricated using the focussed ion beam (FIB) induced technique. Three meander structures with individual line widths of ∼70, ∼300 and ∼450 nm were fabricated for evaluation and comparison of the superconducting properties. The resistance-temperature characteristics of the meanders were measured and analysed down to a temperature of 100 mK. The superconducting properties such as critical temperature (TC) and upper-critical field (HC2) of these wires are in comparison to the reported values of FIB deposited tungsten available in literature. While the normal state resistance increases sharply as the width of the wire decreases, the superconducting transition temperature registered a slight decrease. Significant amount of residual resistance (3.8% of normal state value at 100 mK) was observed for the sample with the lowest width (70 nm). The residual resistance trails as function of temperature was analysed invoking theoretical models governing the phase slip induced dissipations in superconducting nanowires. The results indicated signature of phase slips as the width of the wire decreases: thermally activated phase slips dominant near to the TC and quantum phase slip (QPS) near to TC as well as much below to the TC. The magneto-resistance isotherms indicated quantum phase transitions (QPT); typical of a superconductor-to-insulator transition (SIT) driven by magnetic field. The SIT transition which originates from the intrinsic disorder present in the sample can be tuned by an external parameter such as magnetic field, and can be modelled by standard theories of QPT for quasi 2D or (2 + 1) D XY models. The successful fabrication of meander structures of W using FIB and the demonstration of superconductivity suggest that FIB deposited W can be exploited for many of the technological applications of superconducting nanowires such as superconducting nanowire single photon detectors, bolometers, transition edge sensors and even for quantum current standard employing the QPS phenomenon.

Experimental characterization of SNSPD receiver technology for deep space FSO under laboratory testbed conditions

Deep space Free Space Optical (FSO) systems are an emerging technology, characterized with very high performance in terms of information capacity and communication distances. However, this novel technology demands preliminary experiments, which are unmanageable in real conditions. Regarding this issue, an innovative approach for testing deep space optical communication links in controlled laboratory environment is developed. The proposed testbed is based on fibre optics technology and combines a couple of units, which represent a real deep space FSO link. The parameters of several different photon-counting receivers are discussed. Similar to already demonstrated deep space missions, the implemented optical receiver is Superconducting Nanowire Single Photon Detector (SNSPD) characterized with high single photon sensitivity and detection efficiency. Consequently, in this paper an authentic deep space Poisson channel is theoretically defined, emulated and examined. The description of the Poisson point process is supported by real SNSPD measurements in terms of high efficiency single-photon detection. Moreover, a self-developed unit including Variable Optical Attenuator (VOA) and software controlling the attenuation in the communication loop of the breadboard is applied. Apart from possibility for representing atmospheric-induced fading due to turbulence and Mie scattering effects, the module is utilized as a precise attenuator changing dynamically the optical power based on lookup tables. Addressing the capabilities of VOA unit, detection intensity, detector noise and efficiency versus SNSPD’s bias current is measured. In addition, VOA is used as a very slow optical modulator for testing the restrictions regarding On-Off extinction ratio of the implemented SNSPD detector.

A large active area no longer equals low performance for superconducting nanowire single-photon detectors

New design for a superconducting nanowire single-photon detector yields a large active area 300 micrometers in diameter while meeting the high count rate and detection efficiency values required for LIDAR applications.

Design of a low-filling-factor and polarization-sensitive superconducting nanowire single photon detector with high detection efficiency

We designed a low-filling-factor and polarization-sensitive superconducting nanowire single photon detector (SNSPD), which can achieve a high absorption efficiency and counting rate simultaneously. Numerical simulations show that high absorption efficiency can be achieved by low-filling-factor SNSPDs with a silicon slot and silver reflector. The absorptance of the NbN nanowire for a transverse magnetic (TM) wave at the wavelength of 1550 nm can be 84.4% when the filling factor is only 16.5%, and the corresponding polarization extinction ratio (PER) is 562.9; the absorptance of the NbN nanowire for a transverse electric (TE) wave can be 67.0% when the filling factor is only 11.7%, and the PER is 7.4.