Superconducting Single-photon Detectors Research Articles

Superconducting single photon detectors integrated with single flux quantum readout circuits in a cryocooler

We report the operation of superconducting single photon detectors (SSPDs) with integrated readout electronics based on a single-flux-quantum (SFQ) circuit. The SSPDs were connected to a SFQ readout circuit without bias tee in a cryocooler system, and detection efficiencies (DEs) were measured to verify their correct operation. The DE curves matched well with those measured by conventional readout electronics, and the maximum bias current for normal operation was increased. In addition, we confirmed that the SFQ circuit correctly merged the input signals from two SSPDs. SSPDs with a SFQ readout circuit demonstrated a favorable timing jitter of 50 ps.

New Generation of Nanowire NbN Superconducting Single-Photon Detector for Mid-Infrared

We present a break-through approach to mid-infrared single-photon detection based on nanowire NbN superconducting single-photon detectors (SSPD). Although SSPD became a mature technology for telecom wavelengths (1.3-1.55 μm) its further expansion to mid-infrared wavelength was hampered by low sensitivity above 2 μm. We managed to overcome this limit by reducing the nanowire width to 50 nm, while retaining high superconducting properties and connecting the wires in parallel to produce a voltage response of sufficient magnitude. The new device exhibits 10 times better quantum efficiency at 3.5 μm wavelength than the “standard” SSPD.

Spatial dependence of output pulse delay in a niobium nitride nanowire superconducting single-photon detector

We report on the position-dependent variation in output pulse timing across a superconducting single-photon detector. Our device consists of a single niobium nitride nanowire meander (100 nm width, 4 nm film thickness, 2 mm length). We use a confocal microscope configuration (full width at half maximum-spot size 1.3 μm at 1550 nm wavelength) and a femtosecond laser to study local variations in detection efficiency and output pulse timing. Pulse delays of up to 50 ps across the device correlate to local detection efficiency and resistance variations. This study indicates an underlying mechanism for timing jitter in superconducting nanowire devices.

Single-Photon Counting Detectors

Various new developments for array detectors based on Silicon Single-Photon Avalanche Diodes (SPADs) were reported. Improved Si-SPAD technologies brought higher detection efficiency in the red wavelength range. Higher performance was attained with InGaAs/lnP SPADs by employing fast circuit techniques and by monolithic resistor-detector integration. New lnGaAs(P)/lnP SPAD array detectors provide remarkable performance in the near-infrared range (NIR). Photon detection at longer wavelengths (up to 3.5 μm) was pursued with antimonide SPADs and Superconducting Single-Photon Detectors (SSPD).

Nanowire superconducting single-photon detectors on GaAs for integrated quantum photonic applications

We demonstrate efficient nanowire superconducting single photon detectors (SSPDs) based on NbN thin films grown on GaAs. NbN films ranging from 3 to 5 nm in thickness have been deposited by dc magnetron sputtering on GaAs substrates at 350 °C. These films show superconducting properties comparable to similar films grown on sapphire and MgO. In order to demonstrate the potential for monolithic integration, SSPDs were fabricated and measured on GaAs/AlAs Bragg mirrors, showing a clear cavity enhancement, with a peak quantum efficiency of 18.3% at λ=1300 nm and T=4.2 K.

Demonstration of single-flux-quantum readout operation for superconducting single-photon detectors

A readout circuit using superconducting single-flux-quantum (SFQ) circuits has been developed to realize an independently addressable array of superconducting single-photon detectors (SSPDs). We tested the SFQ readout circuits by connecting with SSPDs. The error rates of readout circuits were below 10−5 for input signal amplitude of greater than 18.2 μA. Detection efficiencies (DEs) for single-photon incidents were measured both with and without the connection of a readout circuit. The observed DEs traced almost the same curves regardless of the connection of the readout circuit, except that the SSPD is likely to latch by connecting the readout circuit.

Spectral dependency of superconducting single photon detectors

We investigate the effect of varying both incoming optical wavelength and width of NbN nanowires on the superconducting single photon detectors (SSPD) detection efficiency. The SSPD are current biased close to critical value and temperature fixed at 4.2 K, far from transition. The experimental results are found to verify with a good accuracy predictions based on the “hot spot model,” whose size scales with the absorbed photon energy. With larger optical power inducing multiphoton detection regime, the same scaling law remains valid, up to the three-photon regime. We demonstrate the validity of applying a limited number of measurements and using such a simple model to reasonably predict any SSPD behavior among a collection of nanowire device widths at different photon wavelengths. These results set the basis for designing efficient single photon detectors operating in the infrared (2–5 μm range).

Operating quantum waveguide circuits with superconducting single-photon detectors

Advanced quantum information science and technology (QIST) applications place exacting demands on optical components. Quantum waveguide circuits offer a route to scalable QIST on a chip. Superconducting single-photon detectors (SSPDs) provide infrared single-photon sensitivity combined with low dark counts and picosecond timing resolution. In this study, we bring these two technologies together. Using SSPDs we observe a two-photon interference visibility of 92.3±1.0% in a silica-on-silicon waveguide directional coupler at λ=804 nm—higher than that measured with silicon detectors (89.9±0.3%). We further operated controlled-NOT gate and quantum metrology circuits with SSPDs. These demonstrations present a clear path to telecom-wavelength quantum waveguide circuits.

Comparison of timing jitter between NbN superconducting single-photon detector and avalanche photodiode

We report the pulse-to-pulse timing jitter measurement of a niobium nitride (NbN) superconducting single-photon detector (SSPD) and a commercially available InGaAs avalanche photodiode (APD) at 1550nm wavelength. A direct comparison of their timing jitter was performed using the same experimental configuration. The measured jitter of the SSPD and the APD are 75 and 84ps at full-width at half-maximum (FWHM), and 138 and 384ps at full-width at tenth-maximum (FWTM), respectively. Although the difference for the FWHM is small, the very small value of the FWTM of the SSPD indicates that the SSPD is more advantageous than the APD for various applications, such as fiber-based quantum key distribution (QKD).

Decoy-state quantum key distribution with polarized photons over 200 km

We report an implementation of decoy-state quantum key distribution (QKD) over 200 km optical fiber cable through photon polarization encoding. This is achieved by constructing the whole QKD system operating at 320 MHz repetition rate, and developing high-speed transmitter and receiver modules. A novel and economic way of synchronization method is designed and incorporated into the system, which allows to work at a low frequency of 40kHz and removes the use of highly precise clock. A final key rate of 15 Hz is distributed within the experimental time of 3089 seconds, by using super-conducting single photon detectors. This is longest decoy-state QKD yet demonstrated up to date. It helps to make a significant step towards practical secure communication in long-distance scope.

Biexciton cascade in telecommunication wavelength quantum dots

We report on polarisation correlation from the cascaded recombination of biexcitons in a quantum dot emitting at a telecommunication wavelength. The fine structure splitting of the exciton state in this InAs/GaAs quantum dot is of the order of 100 μeV and polarisation correlation is expected. Strong polarisation correlation between the biexciton and exciton emission lines is observed under both continuous wave (CW) and pulsed laser excitation so telecom wavelength quantum dots with lower energy splittings could be suitable for entangled photon pair generation. Measurements were performed using nanowire superconducting single photon detectors (SSPDs). SSPDs offer low time-jitter and improve the resolution of features in the correlation spectra, including the asymmetric dip and peak resulting from the cascaded emission with the peak extending more than an order of magnitude above the Poissonian level.

Nanophotonic technologies for single-photon devices

AbstractThe progress in nanofabrication has made possible the realization of optic nanodevices able to handle single photons and to exploit the quantum nature of single-photon states. In particular, quantum cryptography (or more precisely quantum key distribution, QKD) allows unconditionally secure exchange of cryptographic keys by the transmission of optical pulses each containing no more than one photon. Additionally, the coherent control of excitonic and photonic qubits is a major step forward in the field of solid-state cavity quantum electrodynamics, with potential applications in quantum computing. Here, we describe devices for realization of single photon generation and detection based on high resolution technologies and their physical properties. Particular attention will be devoted to the description of single-quantum dot sources based on photonic crystal microcavites optically and electrically driven: the electrically driven devices is an important result towards the realization of single photon source “on demand”. A new class of single photon detectors, based on superconducting nanowires, the superconducting single-photon detectors (SSPDs) are also introduced: the fabrication techniques and the design proposed to obtain large area coverage and photon number-resolving capability are described.

Local anodic oxidation of superconducting NbN thin films by an atomic forcemicroscope

A local anodic oxidation technique has been applied to create oxidized nanowires onsuperconducting NbN thin films using an atomic force microscope (AFM) with aconductive probe. The AFM surface topography shows that both the width and height ofthe oxidized nanowires increase with increasing applied probe voltage under a certainrelative humidity and a probe scan rate. The resistances of the NbN microbridges with andwithout an oxidized nanowire crossing were measured, and the results indicate thatthe oxidized nanowires with height of more than 8 nm are fully oxidized. TheR–T andI–V characteristics of the NbN microbridges with the oxide wire of less than 8 nm were alsoobtained and analyzed. Methods for fabricating devices such as superconducting singlephoton detectors and superconducting hot electron bolometer mixers using this technologyare discussed.

A superconducting NbN detector for neutral nanoparticles

We present a proof-of-principle study of superconducting single photon detectors (SSPD) forthe detection of individual neutral molecules/nanoparticles at low energies. The newdetector is applied to characterize a laser desorption source for biomolecules and allowsretrieval of the arrival time distribution of a pulsed molecular beam containing the aminoacid tryptophan, the polypeptide gramicidin as well as insulin, myoglobin and hemoglobin.We discuss the experimental evidence that the detector is actually sensitive to isolatedneutral particles.

Ultrafast superconducting single-photon detector

The state-of-the-art of the NbN nanowire superconducting single-photon detector technology (SSPD) is presented. The SSPDs exhibit excellent performance at 2 K temperature: 30% quantum efficiency from visible to infrared, negligible dark count rate, single-photon sensitivity up to 5.6 µm. The recent achievements in the development of GHz counting rate devices with photon-number resolving capability is presented.

Continuous high speed coherent one-way quantum key distribution

Quantum key distribution (QKD) is the first commercial quantum technology operating at the level of single quanta and is a leading light for quantum-enabled photonic technologies. However, controlling these quantum optical systems in real world environments presents significant challenges. For the first time, we have brought together three key concepts for future QKD systems: a simple high-speed protocol; high performance detection; and integration both, at the component level and for standard fibre network connectivity. The QKD system is capable of continuous and autonomous operation, generating secret keys in real time. Laboratory and field tests were performed and comparisons made with robust InGaAs avalanche photodiodes and superconducting detectors. We report the first real world implementation of a fully functional QKD system over a 43 dB-loss (150 km) transmission line in the Swisscom fibre optic network where we obtained average real-time distribution rates over 3 hours of 2.5 bps.

Ultrabroadband coherence-domain imaging using parametric downconversion and superconducting single-photon detectors at 1064 nm

Coherence-domain imaging systems can be operated in a single-photon-counting mode, offering low detector noise; this in turn leads to increased sensitivity for weak light sources and weakly reflecting samples. We have demonstrated that excellent axial resolution can be obtained in a photon-counting coherence-domain imaging (CDI) system that uses light generated via spontaneous parametric downconversion (SPDC) in a chirped periodically poled stoichiometric lithium tantalate (chirped-PPSLT) structure, in conjunction with a niobium nitride superconducting single-photon detector (SSPD). The bandwidth of the light generated via SPDC, as well as the bandwidth over which the SSPD is sensitive, can extend over a wavelength region that stretches from 700 to 1500 nm. This ultrabroad wavelength band offers a near-ideal combination of deep penetration and ultrahigh axial resolution for the imaging of biological tissue. The generation of SPDC light of adjustable bandwidth in the vicinity of 1064 nm, via the use of chirped-PPSLT structures, had not been previously achieved. To demonstrate the usefulness of this technique, we construct images for a hierarchy of samples of increasing complexity: a mirror, a nitrocellulose membrane, and a biological sample comprising onion-skin cells.

High-brightness, low-noise, all-fiber photon pair source

We demonstrate an all-fiber photon pair source for the critical telecom C-band. We achieve high pair generation rates in excess of 10 MHz while maintaining coincidence-to-accidental ratios (CARs) greater than 100. This is one of the brightest and lowest-noise photon pair sources ever demonstrated. We achieve the high pair rate through CW-pumped spontaneous four-wave mixing in dispersion-shifted fiber. We achieve the high CAR by cooling the fiber to 4 K to suppress the Raman generation and detecting the photons with low jitter and low dark count superconducting single-photon detectors.

Readout Electronics Using Single-Flux-Quantum Circuit Technology for Superconducting Single-Photon Detector Array

Superconducting single-photon detectors (SSPDs) based on NbN nanowires possess properties such as high counting rate, low dark count rate and small timing jitter, which are promising characteristics for a quantum key distribution system. An SSPD array has recently attracted attention, because it can provide a higher counting rate, and spatial and photon-number resolutions. We propose readout electronics using single-flux-quantum (SFQ) circuits to process a large number of output signals from an SSPD array. We designed and tested an interface circuit between an SSPD and SFQ circuit, and successfully observed SFQ pulse generation for an input pulse with a current amplitude of 17.4 ~ 36.4 muA , which is comparable with an output current amplitude of the SSPD. The interface circuit was also operational for an input pulse duration of 1.6 ns, which is shorter than the typical recovery time of the SSPD.

Development of Superconducting Strip Line Detectors (SSLDs) for Time-of-Flight Mass Spectrometers (TOF-MS)

We have succeeded in obtaining mass spectra of peptides or proteins with superconducting stripline detectors (SSLDs) which have a meander structure similar to so called superconducting single photon detectors (SSPDs). Encouraged by the previous results on the NbN-SSLD for time-of-flight mass spectrometry (TOF-MS), we fabricated other SSLDs from Nb or YBCO thin films. Because of a small London penetration depth, the Nb-based SSLD is expected to have a fast response time. Another promising superconducting material is YBCO which has a critical temperature around 90 K. Operation at higher temperatures will make a noticeable impact on the practical application to MS. The optimum SSLD design for MS should be totally different from that of SSPD in order to realize both of a meaningful sensitive area for high detection efficiency and a reasonably-fast response time for high mass resolution. We made SSLDs with a variety of stripline structures from different materials. One of the key factors for the SSLD design is kinetic inductance. In this study, TOF-MS spectra of biomolecules are presented, and the relationship between SSLD geometry and their performance is discussed.