In this talk, I will present the latest results in superconducting single-photon detectors. Superconducting wires have remarkable sensitivity to single-photons and are a reliable and high-performance technology with significant impact on the quantum information research community. However, increasingly applications as diverse as detection of high-energy particles and searches for dark matter are being pursued. Finally, research on these nanowires has permitted their use for basic electronics circuits such as comparators, shift registers, and counters. We will review these and other topics surrounding the development of nanowire single-photon detectors.
Superconducting single-photon detectors are a key technology for quantum information science, being of particular use for quantum key distribution and photonics-based quantum computing. However, the biasing, readout, and signal processing associated with the detector is typically handled by off-chip conventional semiconductor electronics. Increasingly, this solution is proving problematic: such electronics consume large amounts of power and are cumbersome to integrate on the same chip as the detectors. Superconducting classical electronics relying on Josephson junctions are an alternative, but require an integrated fabrication process, which adds complexity to the device. An alternative is to use the superconducting nanowires themselves, in the form of “cryotrons”, an alternative to Josephson junction superconducting switches first proposed in the 1950s, but recently experiencing renewed interest with scaling to the nanometer length scale. These technologies and applications of them to SNSPD readout and signal processing will be discussed.
We describe the requirements and associated technology development plan for the communications data link from low mass interstellar probes. This work is motivated by several proposed deep space and interstellar missions with an emphasis on the Breakthrough Starshot project. The Starshot project is an effort to send the first low mass interstellar probes to nearby star systems and transmit back scientific data acquired during system transit within the time scale of a human lifetime. The about 104-fold increase in distance to nearby stars compared to the outer planets of our solar system requires a new form of propulsion to reach speeds of approximately 20% of the speed of light. The proposed use of a low mass sailcraft places strong constraints on the mass and power for the Starshot communications system. We compare the communications systems in current and upcoming solar system probes, New Horizons and Psyche, against the requirements for Starshot and define Figures of Merit for the communications capability in terms of data downlink rate multiplied by distance squared per unit mass. We describe current and future technology developments required for the on-board transmitter (signal generation, signal distribution, and beamforming) and for the near-Earth communications receiver (low-cost large aperture telescopes, high resolution spectrometers, and single photon counting detectors). We also describe a roadmap for technology development to meet the goals for future interstellar communications.
Superconducting nanowires operating at temperatures of a few degrees Kelvin can be biased so that a single photon--even one in the infrared--will initiate a sudden transition into a resistive state that is easily sensed by conventional amplifiers. The resulting signal preserves photon-arrival timing at the few-picosecond level and adds virtually no readout noise. Imagers are now being developed in this technology for a range of future applications. In this talk, I will present the current state-of-the-art of this technology.
Superconducting nanowire single-photon detectors (SNSPDs) have distinguished themselves as a near-optimal choice for a range of quantum information applications, including integrated photonics and quantum key distribution. But the most recent demands from the quantum domain are stretching their capabilities. In particular, photon number resolution has not been readily available in high-performance variants of the devices, and superconducting nanowires were generally thought not to be capable of intrinsic photon number resolution. Recently, significant results in this area have shown that photon number resolution is quite practical with SNSPDs. In addition, wider nanowires have shown good performance, suggesting that the devices can be fabricated using standard photolithography equipment. In this talk, I will review the SNSPD technology, as well as discuss our latest results.
Superconducting nanowires and nanostrips have been used extensively in single-photon detection and have recently demonstrated the capability for photon-number resolution. These devices can also find use for microwave analog and digital superconducting electronics for purposes such as signal processing and multiplexing, and potentially for applications to readout of superconductive quantum computing. This talk will discuss novel electronics and photodetection devices based on superconducting nanowires.
Superconducting nanowires are currently a key technology for photon sensing, with key performance metrics exceeding those of most competing technologies. For example, recently detector timing resolution of just 3 ps for single visible photons was demonstrated. In addition, infrared sensitivity has long been a key advantage of these techniques. But the field continues to change rapidly, with interesting architectures emerging that promise increased functionality in the same form factor. For example, imaging, photon-number-resolution, and spectroscopy are all promising directions the field is now pursuing. In this review, I will explain the technology, applications, and background device physics, but also touch on some of the latest new developments.
We describe the performance of detector modules containing silicon single photon avalanche photodiodes (SPADs) and superconducting nanowire single photon detectors (SNSPDs) to be used for intensity interferometry. The SPADs are mounted in fiber-coupled and free-space coupled packages. The SNSPDs are mounted in a small liquid helium cryostat coupled to single mode fiber optic cables which pass through a hermetic feed-through. The detectors are read out with microwave amplifiers and FPGA-based coincidence electronics. We present progress on measurements of intensity correlations from incoherent sources including gas-discharge lamps and stars with these detectors. From the measured laboratory performance of the correlation system, we estimate the sensitivity to intensity correlations from stars using commercial telescopes and larger existing research telescopes.
KEYWORDS: Sensors, Single photon detectors, Superconductors, Photons, Temperature metrology, Optical testing, Very large scale integration, Signal detection, Integrated circuits, Nanowires
Today Superconducting Nanowire Single-Photon Detectors (SNSPDs) are commonly used in different photon-starved applications, including testing and diagnostics of VLSI circuits. Detecting very faint signals in the near-infrared wavelength range requires not only good detection efficiency, but also very low Dark Count Rate (DCR) and jitter. For example, low noise is crucial to enable ultra-low voltage optical testing of integrated circuits. The effect of detector temperature and background thermal radiation on the noise of superconducting single-photon detectors made of NbN meanders is studied in this paper. It is shown that two different regimes can be identified in the DCR vs. bias current characteristics. At high bias, the dark count rate is dominated by the intrinsic noise of the detector, while at low bias current it is dominated by the detection of stray photons that get onto the SNSPD. Changing the detector temperature changes its switching current and only affects the high bias branch of the characteristics: a reduction of the DCR can be achieved by lowering the SNSPD base temperature. On the other hand, changing the temperature of the single-photon light source (e.g. the VLSI circuit under test) only affects the low bias regime: a lower target temperature leads to a smaller DCR.
Superconducting circuits comprising SNSPDs placed in parallel—superconducting nanowire avalanche photodetectors, or SNAPs—have previously been demonstrated to improve the output signal-to-noise ratio (SNR) by increasing the critical current. In this work, we employ a 2-SNAP superconducting circuit with narrow (40 nm) niobium nitride (NbN) nanowires to improve the system detection efficiency to near-IR photons while maintaining high SNR. Additionally, while previous 2-SNAP demonstrations have added external choke inductance to stabilize the avalanching photocurrent, we show that the external inductance can be entirely folded into the active area by cascading 2-SNAP devices in series to produce a greatly increased active area. We fabricated series-2-SNAP (s2-SNAP) circuits with a nanowire length of 20 μm with cascades of 2-SNAPs providing the choke inductance necessary for SNAP operation. We observed that (1) the detection efficiency saturated at high bias currents, and (2) the 40 nm 2-SNAP circuit critical current was approximately twice that for a 40 nm non-SNAP configuration.
KEYWORDS: Finite element methods, Gold, Near field, Near field optics, Reflectors, Superconductors, Single photon detectors, Reflectivity, Transmittance, Nanowires
The optimum orientations were determined for polarized light illumination of three superconducting nanowire single-photon detector (SNSPD) designs consisting of niobium-nitride (NbN) stripes with dimensions according to conventional devices in 200 nm periodic pattern: (1) standing in air (bare-SNSPD), (2) below ∼quarter-wavelength hydrogen-silsesquioxane (HSQ) filled nano-cavity (DC-SNSPD), and (3) below HSQ-filled nano-cavity closed by a thin gold reflector (OC-SNSPD). Computations showed that the optical response and near-field distribution vary significantly with polar angle φ, and these variations are analogous across all azimuthal angles γ, but are fundamentally different in different device designs. Larger absorptance is attainable due to p-polarized illumination of NbN patterns in P-orientation, while s-polarized illumination results in higher absorptance in S-orientation. As a result of p-polarized illumination, a global NbN absorptance maximum appears in bare-SNSPD at polar angle corresponding to attenuated total internal reflection (ATIR); in DC-SNSPD exactly at total internal reflection (TIR); and at perpendicular incidence in OC-SNSPD. S-polarized illumination results in a global NbN absorptance maximum in bare-SNSPD at TIR; in DC-SNSPD at polar angle corresponding to ATIR phenomenon; while large and almost polar angle independent absorptance is attainable in OC-SNSPD at small tilting.
KEYWORDS: Near field optics, Gold, Reflectors, Finite element methods, Near field, Interfaces, Infrared radiation, Single photon detectors, Transmittance, Infrared detectors
The illumination-angle-dependent absorptance was determined for three types of superconducting-nanowire singlephoton
detector (SNSPD) designs: 1. periodic bare niobium-nitride (NbN) stripes with dimensions of conventional
SNSPDs, 2. the same NbN patterns integrated with ~quarter-wavelength hydrogensilsesquioxane-filled nano- cavity, 3.
similar cavity-integrated structures covered by a thin gold reflector. A three-dimensional finite-element method was
applied to determine the optical response and near-field distribution as a function of p-polarized light illumination
orientations specified by polar-angle, φ, and azimuthal-angle, γ. The numerical results proved that the NbN absorptance
might be maximized via simultaneous optimization of the polar and azimuthal illumination angles. Complementary
transfer-matrix-method calculations were performed on analogous film-stacks to uncover the phenomena contributing to
the appearance of extrema on the optical response of NbN-patterns in P-structure-configuration. This comparative study
showed that the absorptance of bare NbN patterns is zero at the angle corresponding to total internal reflection (TIR). In
cavity-integrated structures the NbN absorptance curve indicates a maximum at the same orientation due to the phase
shift introduced by the quarter-wavelength HSQ layer. The reflector promotes the NbN absorptance at small polar
angles, but the available absorptance is limited by attenuated TIR in polar angle-intervals, where surface modes are
excited on the gold film.
Block copolymers have been proposed for self-assembled nanolithography because they can spontaneously form
well-ordered nanoscale periodic patterns of lines or dots in a rapid, low-cost process. By templating the selfassembly,
patterns of increasing complexity can be generated, for example arrays of lines with bends or
junctions. This offers the possibility of using a sparse template, written by electron-beam lithography or other
means, to organize a dense array of nanoscale features. Pattern transfer is simplified if one block is etch resistant
and one easily removable, and in this work we use a diblock copolymer or a triblock terpolymer with one Sicontaining
block such as polydimethylsiloxane or polyferrocenylsilane, and one or two organic blocks such as
polystyrene or polyisoprene. Removal of the organic block(s) with an oxygen plasma leaves a pattern of Sicontaining
material which can be used as an etch mask for subsequent pattern transfer to make metallization lines
or magnetic nanostructures with feature sizes below 10 nm and periodicity below 20 nm.
Superconducting nanowire single photon detectors have recently been demonstrated as viable candidates for photon-counting
optical receivers operating at data rates in excess of 100 Mbit/s. In this paper, we discuss techniques for
extending these data rates to rates > 1 Gbit/s. We report on a recent demonstration of a 2-element nanowire detector
array operating at a source data rate of 1.25 Gbit/s. We also describe techniques for emulating larger arrays of detectors
using a single detector. We use these techniques to demonstrate photon-counting receiver operation at data rates from
780-Mbit/s to 2.5 Gbit/s with sensitivities ranging from 1.1 to 7.1 incident photons per bit.
The sensitivity of a high-rate photon-counting optical communications link depends on the performance of the photon counter used to detect the optical signal. In this paper, we focus on ways to reduce the effect of blocking, which is loss due to time periods in which the photon counter is inactive following a preceding detection event. This blocking loss can be reduced by using an array of photon counting detectors or by using photon counters with a shorter inactive period. Both of these techniques for reducing the blocking loss can be employed by using a multi-element superconducting nanowire single-photon detector. Two-element superconducting nanowire single-photon detectors are used to demonstrate error-free photon counting optical communication at data rates of 781 Mbit/s and 1.25 Gbit/s.
This paper describes the formation of nanometer-scale features in gold and silicon substrates. The features in gold were made by using a self-assembled monolayer (SAM) of nonanethiolate on gold as a resist damaged by neutral cesium atoms. A SAM resist of octyltrichlorosilane on silicon dioxide was used as a resist sensitive to cesium atoms in order to fabricate features in silicon. A silicon nitride membrane perforated with nm- and micrometers -scale holes was used to pattern the atomic beam. Etching transferred the pattern formed in the SAM layer into the underlying substrate. Features of < 100-nm size were etched into the gold and silicon substrates. Investigations of the reflectivity of samples of nonanethiolate on gold, exposed to the atomic beam without a mask and subsequently etched, revealed that the resist-etch system exhibited a minimum threshold dose of cesium for damage; at doses lower than approximately 3 monolayers, the damage was insufficient to allow penetration of the SAM by the etching solution. The threshold dose for damage of the octyltrichlorosilane SAM on silicon dioxide is under investigation.
Kent Johnson, Karl Berggren, Andrew Black, Charles Black, Arthur Chu, Nynke Dekker, D. Ralph, Joseph Thywissen, Rebecca Younkin, Mara Goff Prentiss, Michael Tinkham, George Whitesides
We describe the fabrication of approximately 70-nm structures in silicon, silicon dioxide, and gold substrates by the exposure of the substrates to a beam of metastable argon atoms in the presence of dilute vapors of trimethylpentaphenyltrisiloxane, the dominant constituent of the diffusion pump oil used in these experiments. The atoms release their internal energy upon contacting the siloxanes physisorbed on the surface of the substrate, and this release causes the formation of a predominantly carbon-based resist. To demonstrate the resolution of the resist formation process, the atomic beam was patterned by a silicon nitride membrane, and the pattern formed in the resist material was transferred to the substrates by chemical etching. Simultaneous exposure of large areas (44 cm2) was also demonstrated. The sensitivity of the resist formation to the internal energy stored in the atom allows a new pattern formation technique based on spatially dependent optical de-excitation of the metastable atoms.
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