Showing 1–34 of 34 results for author: Nam, S W

WSi weak link element with a non-sinusoidal current-phase relation

Authors: Sarah Garcia Jones, Trevyn F. Q. Larson, Sai Pavan Chitta, Heli Vora, Varun Verma, Sae Woo Nam, José Aumentado, Jens Koch, Raymond W. Simmonds, András Gyenis

Abstract: Nonlinearity is an essential ingredient for encoding quantum states with non-uniform energy spacing, implementing coherent quantum gates, reading out qubits, amplifying, and mixing electromagnetic signals. In this work, we demonstrate the nonlinear behavior of a constriction fabricated from an amorphous, high-kinetic inductance material, tungsten silicide, embedded in a three-dimensional RF-SQUID.… ▽ More Nonlinearity is an essential ingredient for encoding quantum states with non-uniform energy spacing, implementing coherent quantum gates, reading out qubits, amplifying, and mixing electromagnetic signals. In this work, we demonstrate the nonlinear behavior of a constriction fabricated from an amorphous, high-kinetic inductance material, tungsten silicide, embedded in a three-dimensional RF-SQUID. We find that the results are consistent with the weak link behaving as a Josephson junction with a sawtooth-like current-phase relation or a quantum phase slip element. Finally, we measure relaxation times of the metastable, persistent-current states trapped in the local minima of the potential. △ Less

Submitted 19 May, 2026; originally announced May 2026.

Tungsten Germanide Superconducting Nanowire Single-Photon Detectors with Saturated Internal Detection Efficiency at Wavelengths up to 29 μm

Authors: Benedikt Hampel, Daniel Kuznesof, Andrew S. Mueller, Sahil R. Patel, Robert H. Hadfield, Emma E. Wollman, Matthew D. Shaw, Dirk Schwarzer, Alec M. Wodtke, Khalid Hossain, Allison V. Mis, Alexana Roshko, Richard P. Mirin, Sae Woo Nam, Martin J. Stevens, Varun B. Verma

Abstract: Superconducting nanowire single-photon detectors (SNSPDs) are among the most sensitive single-photon detectors available and have the potential to transform fields ranging from infrared astrophysics to molecular spectroscopy. However, extending their performance into the mid-infrared spectral region - crucial for applications such as exoplanet transit spectroscopy and vibrational fingerprinting of… ▽ More Superconducting nanowire single-photon detectors (SNSPDs) are among the most sensitive single-photon detectors available and have the potential to transform fields ranging from infrared astrophysics to molecular spectroscopy. However, extending their performance into the mid-infrared spectral region - crucial for applications such as exoplanet transit spectroscopy and vibrational fingerprinting of molecules - has remained a major challenge, primarily due to material limitations and scalability constraints. Here, we report on the development of SNSPDs based on tungsten germanide, a novel material system that combines high mid-infrared sensitivity with compatibility for large-scale fabrication. Our detectors exhibit saturated internal detection efficiency at wavelengths up to 29 μm, while using 2.7x thicker films (8 nm vs 3 nm) and up to 4.5x wider nanowires (360 nm vs 80 nm) compared to mid-infrared-optimized SNSPDs fabricated from tungsten silicide. This advance will enable scalable, high-performance single-photon detection in a spectral region that was previously inaccessible, opening new frontiers in remote sensing, thermal imaging, environmental monitoring, molecular physics, and astronomy. △ Less

Submitted 16 June, 2026; v1 submitted 25 November, 2025; originally announced November 2025.

Comments: 8 pages, 6 figures, Published in APL Photonics 11(6): 066112 (2026) (doi: 10.1063/5.0331641)

Journal ref: APL Photonics 11 (6): 066112 (2026)

Localized quasiparticles in a fluxonium with quasi-two-dimensional amorphous kinetic inductors

Authors: Trevyn F. Q. Larson, Sarah Garcia Jones, Tamás Kalmár, Pablo Aramburu Sanchez, Sai Pavan Chitta, Varun Verma, Kristen Genter, Katarina Cicak, Sae Woo Nam, Gergő Fülöp, Jens Koch, Ray W. Simmonds, András Gyenis

Abstract: Disordered superconducting materials with high kinetic inductance are an important resource to generate nonlinearity in quantum circuits and create high-impedance environments. In thin films fabricated from these materials, the combination of disorder and the low effective dimensionality leads to increased order parameter fluctuations and enhanced kinetic inductance values. Among the challenges of… ▽ More Disordered superconducting materials with high kinetic inductance are an important resource to generate nonlinearity in quantum circuits and create high-impedance environments. In thin films fabricated from these materials, the combination of disorder and the low effective dimensionality leads to increased order parameter fluctuations and enhanced kinetic inductance values. Among the challenges of harnessing these compounds in coherent devices are their proximity to the superconductor-insulator phase transition, the presence of broken Cooper pairs, and the two-level systems located in the disordered structure. In this work, we fabricate tungsten silicide wires from quasi-two-dimensional films with one spatial dimension smaller than the superconducting coherence length and embed them into microwave resonators and fluxonium qubits, where the kinetic inductance provides the inductive part of the circuits. We study the dependence of loss on the frequency, disorder, and geometry of the device, and find that the loss increases with the level of disorder and is dominated by the localized quasiparticles trapped in the spatial variations of the superconducting gap. △ Less

Submitted 10 April, 2025; originally announced April 2025.

Journal ref: Nat Commun 17, 3022 (2026)

A 64-pixel mid-infrared single-photon imager based on superconducting nanowire detectors

Authors: Benedikt Hampel, Richard P. Mirin, Sae Woo Nam, Varun B. Verma

Abstract: A large-format mid-infrared single-photon imager with very low dark count rates would enable a broad range of applications in fields like astronomy and chemistry. Superconducting nanowire single-photon detectors (SNSPDs) are a mature photon-counting technology as demonstrated by their figures of merit. However, scaling SNSPDs to large array sizes for mid-infrared applications requires sophisticate… ▽ More A large-format mid-infrared single-photon imager with very low dark count rates would enable a broad range of applications in fields like astronomy and chemistry. Superconducting nanowire single-photon detectors (SNSPDs) are a mature photon-counting technology as demonstrated by their figures of merit. However, scaling SNSPDs to large array sizes for mid-infrared applications requires sophisticated readout architectures in addition to superconducting materials development. In this work, an SNSPD array design that combines a thermally coupled row-column multiplexing architecture with a thermally coupled time-of-flight transmission line was developed for mid-infrared applications. The design requires only six cables and can be scaled to larger array sizes. The demonstration of a 64-pixel array shows promising results for wavelengths between $\mathrm{3.4\,μm}$ and $\mathrm{10\,μm}$, which will enable the use of this single-photon detector technology for a broad range of new applications. △ Less

Submitted 28 September, 2023; originally announced September 2023.

Comments: 7 pages, 3 figures, 1 page supplementary material. The following article has been submitted to Applied Physics Letters

Journal ref: Appl. Phys. Lett. 124, 042602 (2024)

A superconducting-nanowire single-photon camera with 400,000 pixels

Authors: Bakhrom G. Oripov, Dana S. Rampini, Jason Allmaras, Matthew D. Shaw, Sae Woo Nam, Boris Korzh, Adam N. McCaughan

Abstract: For the last 50 years, superconducting detectors have offered exceptional sensitivity and speed for detecting faint electromagnetic signals in a wide range of applications. These detectors operate at very low temperatures and generate a minimum of excess noise, making them ideal for testing the non-local nature of reality, investigating dark matter, mapping the early universe, and performing quant… ▽ More For the last 50 years, superconducting detectors have offered exceptional sensitivity and speed for detecting faint electromagnetic signals in a wide range of applications. These detectors operate at very low temperatures and generate a minimum of excess noise, making them ideal for testing the non-local nature of reality, investigating dark matter, mapping the early universe, and performing quantum computation and communication. Despite their appealing properties, however, there are currently no large-scale superconducting cameras - even the largest demonstrations have never exceeded 20 thousand pixels. This is especially true for one of the most promising detector technologies, the superconducting nanowire single-photon detector (SNSPD). These detectors have been demonstrated with system detection efficiencies of 98.0%, sub-3-ps timing jitter, sensitivity from the ultraviolet (250nm) to the mid-infrared (10um), and dark count rates below 6.2e-6 counts per second (cps), but despite more than two decades of development they have never achieved an array size larger than a kilopixel. Here, we report on the implementation and characterization of a 400,000 pixel SNSPD camera, a factor of 400 improvement over the previous state-of-the-art. The array spanned an area 4x2.5 mm with a 5x5um resolution, reached unity quantum efficiency at wavelengths of 370 nm and 635 nm, counted at a rate of 1.1e5 cps, and had a dark count rate of 1e-4 cps per detector (corresponding to 0.13 cps over the whole array). The imaging area contains no ancillary circuitry and the architecture is scalable well beyond the current demonstration, paving the way for large-format superconducting cameras with 100% fill factors and near-unity detection efficiencies across a vast range of the electromagnetic spectrum. △ Less

Submitted 15 June, 2023; originally announced June 2023.

Trap-Integrated Superconducting Nanowire Single-Photon Detectors with Improved RF Tolerance for Trapped-Ion Qubit State Readout

Authors: Benedikt Hampel, Daniel H. Slichter, Dietrich Leibfried, Richard P. Mirin, Sae Woo Nam, Varun B. Verma

Abstract: State readout of trapped-ion qubits with trap-integrated detectors can address important challenges for scalable quantum computing, but the strong rf electric fields used for trapping can impact detector performance. Here, we report on NbTiN superconducting nanowire single-photon detectors (SNSPDs) employing grounded aluminum mirrors as electrical shielding that are integrated into linear surface-… ▽ More State readout of trapped-ion qubits with trap-integrated detectors can address important challenges for scalable quantum computing, but the strong rf electric fields used for trapping can impact detector performance. Here, we report on NbTiN superconducting nanowire single-photon detectors (SNSPDs) employing grounded aluminum mirrors as electrical shielding that are integrated into linear surface-electrode rf ion traps. The shielded SNSPDs can be successfully operated at applied rf trapping potentials of up to $\mathrm{54\,V_{peak}}$ at $\mathrm{70\,MHz}$ and temperatures of up to $\mathrm{6\,K}$, with a maximum system detection efficiency of $\mathrm{68\,\%}$. This performance should be sufficient to enable parallel high-fidelity state readout of a wide range of trapped ion species in typical cryogenic apparatus. △ Less

Submitted 2 February, 2023; originally announced February 2023.

Comments: 6 pages, 4 figures. The following article has been submitted to Applied Physics Letters

Journal ref: Appl. Phys. Lett. 122, 174001 (2023)

Demonstration of Superconducting Optoelectronic Single-Photon Synapses

Authors: Saeed Khan, Bryce A. Primavera, Jeff Chiles, Adam N. McCaughan, Sonia M. Buckley, Alexander N. Tait, Adriana Lita, John Biesecker, Anna Fox, David Olaya, Richard P. Mirin, Sae Woo Nam, Jeffrey M. Shainline

Abstract: Superconducting optoelectronic hardware is being explored as a path towards artificial spiking neural networks with unprecedented scales of complexity and computational ability. Such hardware combines integrated-photonic components for few-photon, light-speed communication with superconducting circuits for fast, energy-efficient computation. Monolithic integration of superconducting and photonic d… ▽ More Superconducting optoelectronic hardware is being explored as a path towards artificial spiking neural networks with unprecedented scales of complexity and computational ability. Such hardware combines integrated-photonic components for few-photon, light-speed communication with superconducting circuits for fast, energy-efficient computation. Monolithic integration of superconducting and photonic devices is necessary for the scaling of this technology. In the present work, superconducting-nanowire single-photon detectors are monolithically integrated with Josephson junctions for the first time, enabling the realization of superconducting optoelectronic synapses. We present circuits that perform analog weighting and temporal leaky integration of single-photon presynaptic signals. Synaptic weighting is implemented in the electronic domain so that binary, single-photon communication can be maintained. Records of recent synaptic activity are locally stored as current in superconducting loops. Dendritic and neuronal nonlinearities are implemented with a second stage of Josephson circuitry. The hardware presents great design flexibility, with demonstrated synaptic time constants spanning four orders of magnitude (hundreds of nanoseconds to milliseconds). The synapses are responsive to presynaptic spike rates exceeding 10 MHz and consume approximately 33 aJ of dynamic power per synapse event before accounting for cooling. In addition to neuromorphic hardware, these circuits introduce new avenues towards realizing large-scale single-photon-detector arrays for diverse imaging, sensing, and quantum communication applications. △ Less

Submitted 20 April, 2022; originally announced April 2022.

Comments: 23 pages, 20 figures

The thermally-coupled imager: A scalable readout architecture for superconducting nanowire single photon detectors

Authors: Adam N. McCaughan, Yao Zhai, Boris Korzh, Jason P. Allmaras, Bakhrom G. Oripov, Matthew D. Shaw, Sae Woo Nam

Abstract: Although superconducting nanowire single-photon detectors (SNSPDs) are a promising technology for quantum optics, metrology, and astronomy, they currently lack a readout architecture that is scalable to the megapixel regime and beyond. In this work, we have designed and demonstrated such an architecture for SNSPDs, called the thermally-coupled imager (TCI). The TCI uses a combination of time-of-fl… ▽ More Although superconducting nanowire single-photon detectors (SNSPDs) are a promising technology for quantum optics, metrology, and astronomy, they currently lack a readout architecture that is scalable to the megapixel regime and beyond. In this work, we have designed and demonstrated such an architecture for SNSPDs, called the thermally-coupled imager (TCI). The TCI uses a combination of time-of-flight delay lines and thermal coupling to create a scalable architecture that can scale to large array sizes, allows neighboring detectors to operate independently, and requires only four microwave readout lines to operate no matter the size of the array. We give an overview of how the architecture functions, and demonstrate a proof-of-concept $32\times32$ imaging array. The array was able to image a free-space focused spot at 373 nm, count at 9.6 Mcps, and resolve photon location with greater than 99.83\% distinguishability. △ Less

Submitted 9 December, 2021; originally announced December 2021.

New constraints on dark matter from superconducting nanowires

Authors: Yonit Hochberg, Benjamin V. Lehmann, Ilya Charaev, Jeff Chiles, Marco Colangelo, Sae Woo Nam, Karl K. Berggren

Abstract: Superconducting nanowires, a mature technology originally developed for quantum sensing, can be used as a target and sensor with which to search for dark matter interactions with electrons. Here we report on a 180-hour measurement of a tungsten silicide superconducting nanowire device with a mass of 4.3 nanograms. We use this to place new constraints on dark matter--electron interactions, includin… ▽ More Superconducting nanowires, a mature technology originally developed for quantum sensing, can be used as a target and sensor with which to search for dark matter interactions with electrons. Here we report on a 180-hour measurement of a tungsten silicide superconducting nanowire device with a mass of 4.3 nanograms. We use this to place new constraints on dark matter--electron interactions, including the strongest terrestrial constraints to date on sub-MeV (sub-eV) dark matter that interacts with electrons via scattering (absorption) processes. △ Less

Submitted 20 December, 2022; v1 submitted 4 October, 2021; originally announced October 2021.

Comments: 5 pages + appendices, 5 figures. Matched published version

Journal ref: Phys. Rev. D 106, 112005 (2022)

Size dependent nature of the magnetic-field driven superconductor-to-insulator quantum-phase transitions

Authors: Xiaofu Zhang, Adriana E. Lita, Huanlong Liu, Varun B. Verma, Qiang Zhou, Sae Woo Nam, Andreas Schilling

Abstract: The nature of the magnetic-field driven superconductor-to-insulator quantum-phase transition in two-dimensional systems at zero temperature has been under debate since the 1980s, and became even more controversial after the observation of a quantum-Griffiths singularity. Whether it is induced by quantum fluctuations of the superconducting phase and the localization of Cooper pairs, or is directly… ▽ More The nature of the magnetic-field driven superconductor-to-insulator quantum-phase transition in two-dimensional systems at zero temperature has been under debate since the 1980s, and became even more controversial after the observation of a quantum-Griffiths singularity. Whether it is induced by quantum fluctuations of the superconducting phase and the localization of Cooper pairs, or is directly driven by depairing of these pairs, remains an open question. We herein experimentally demonstrate that in weakly-pinning systems and in the limit of infinitely wide films, a sequential superconductor-to-Bose insulator-to-Fermi insulator quantum-phase transition takes place. By limiting their size smaller than the effective penetration depth, however, the vortex interaction alters, and the superconducting state re-enters the Bose-insulating state. As a consequence, one observes a direct superconductor-to-Fermi insulator in the zero-temperature limit. In narrow films, the associated critical-exponent products diverge along the corresponding phase boundaries with increasing magnetic field, which is a hallmark of the quantum-Griffiths singularity. △ Less

Submitted 13 May, 2021; originally announced May 2021.

Comments: 6 main figures, 11 supplementary Figures, 2 supplementary Movies. This is a preprint of an article published in Communications Physics. The final authenticated open-access version with updated figures and text is available for free from May 14, 2021 at https://doi.org/10.1038/s42005-021-00602-7

PHIDL: Python CAD layout and geometry creation for nanolithography

Authors: A. N. McCaughan, A. M. Tait, S. M. Buckley, D. M. Oh, J. T. Chiles, J. M. Shainline, S. W. Nam

Abstract: Computer-aided design (CAD) has become a critical element in the creation of nanopatterned structures and devices. In particular, with the increased adoption of easy-to-learn programming languages like Python there has been a significant rise in the amount of lithographic geometries generated through scripting and programming. However, there are currently unaddressed gaps in usability for open-sou… ▽ More Computer-aided design (CAD) has become a critical element in the creation of nanopatterned structures and devices. In particular, with the increased adoption of easy-to-learn programming languages like Python there has been a significant rise in the amount of lithographic geometries generated through scripting and programming. However, there are currently unaddressed gaps in usability for open-source CAD tools -- especially those in the GDSII design space -- that prevent wider adoption by scientists and students who might otherwise benefit from scripted design. For example, constructing relations between adjacent geometries is often much more difficult than necessary -- spacing a resonator structure a few micrometers from a readout structure often requires manually-coding the placement arithmetic. While inconveniences like this can be overcome by writing custom functions, they are often significant barriers to entry for new users or those less familiar with programming. To help streamline the design process and reduce barrier to entry for scripting designs, we have developed PHIDL, an open-source GDSII-based CAD tool for Python 2 and 3. △ Less

Submitted 1 March, 2021; originally announced March 2021.

Journal ref: J. Vac. Sci. Technol. B 39, 062601 (2021)

State Readout of a Trapped Ion Qubit Using a Trap-Integrated Superconducting Photon Detector

Authors: S. L. Todaro, V. B. Verma, K. C. McCormick, D. T. C. Allcock, R. P. Mirin, D. J. Wineland, S. W. Nam, A. C. Wilson, D. Leibfried, D. H. Slichter

Abstract: We report high-fidelity state readout of a trapped ion qubit using a trap-integrated photon detector. We determine the hyperfine qubit state of a single $^9$Be$^+$ ion held in a surface-electrode rf ion trap by counting state-dependent ion fluorescence photons with a superconducting nanowire single-photon detector (SNSPD) fabricated into the trap structure. The average readout fidelity is 0.9991(1… ▽ More We report high-fidelity state readout of a trapped ion qubit using a trap-integrated photon detector. We determine the hyperfine qubit state of a single $^9$Be$^+$ ion held in a surface-electrode rf ion trap by counting state-dependent ion fluorescence photons with a superconducting nanowire single-photon detector (SNSPD) fabricated into the trap structure. The average readout fidelity is 0.9991(1), with a mean readout duration of 46 $μ$s, and is limited by the polarization impurity of the readout laser beam and by off-resonant optical pumping. Because there are no intervening optical elements between the ion and the detector, we can use the ion fluorescence as a self-calibrated photon source to determine the detector quantum efficiency and its dependence on photon incidence angle and polarization. △ Less

Submitted 31 July, 2020; originally announced August 2020.

Comments: 15 pages, 11 figures, including supplemental material

Journal ref: Phys. Rev. Lett. 126, 010501 (2021)

Strong suppression of the resistivity near the transition to superconductivity in narrow micro-bridges in external magnetic fields

Authors: Xiaofu Zhang, Adriana E. Lita, Konstantin Smirnov, HuanLong Liu, Dong Zhu, Varun B. Verma, Sae Woo Nam, Andreas Schilling

Abstract: We have investigated a series of superconducting bridges based on homogeneous amorphous WSi and MoSi films, with bridge widths w ranging from 2 um to 1000 um and film thicknesses d ~ 4-6 nm and 100 nm. Upon decreasing the bridge widths below the respective Pearl lengths, we observe in all cases distinct changes in the characteristics of the resistive transitions to superconductivity. For each of t… ▽ More We have investigated a series of superconducting bridges based on homogeneous amorphous WSi and MoSi films, with bridge widths w ranging from 2 um to 1000 um and film thicknesses d ~ 4-6 nm and 100 nm. Upon decreasing the bridge widths below the respective Pearl lengths, we observe in all cases distinct changes in the characteristics of the resistive transitions to superconductivity. For each of the films, the resistivity curves R(B,T) separate at a well-defined and field-dependent temperature T*(B) with decreasing the temperature, resulting in a dramatic suppression of the resistivity and a sharpening of the transitions with decreasing bridge width w. The associated excess conductivity in all the bridges scales as 1/w, which may suggest the presence of a highly conducting region that is dominating the electric transport in narrow bridges. We argue that this effect can only be observed in materials with sufficiently weak vortex pinning. △ Less

Submitted 21 February, 2020; v1 submitted 6 September, 2019; originally announced September 2019.

Journal ref: Phys. Rev. B 101, 060508 (2020)

Quantum simulations with multiphoton Fock states

Authors: T. Sturges, T. McDermott, A. Buraczewski, W. R. Clements, J. J. Renema, S. W. Nam, T. Gerrits, A. Lita, W. S. Kolthammer, A. Eckstein, I. A. Walmsley, M. Stobińska

Abstract: Quantum simulations are becoming an essential tool for studying complex phenomena, e.g. quantum topology, quantum information transfer, and relativistic wave equations, beyond the limitations of analytical computations and experimental observations. To date, the primary resources used in proof-of-principle experiments are collections of qubits, coherent states or multiple single-particle Fock stat… ▽ More Quantum simulations are becoming an essential tool for studying complex phenomena, e.g. quantum topology, quantum information transfer, and relativistic wave equations, beyond the limitations of analytical computations and experimental observations. To date, the primary resources used in proof-of-principle experiments are collections of qubits, coherent states or multiple single-particle Fock states. Here we show the first quantum simulation performed using genuine higher-order Fock states, with two or more indistinguishable particles occupying the same bosonic mode. This was implemented by interfering pairs of Fock states with up to five photons on an interferometer, and measuring the output states with photon-number-resolving detectors. Already this resource-efficient demonstration reveals new topological matter, simulates non-linear systems and elucidates a perfect quantum transfer mechanism which can be used to transport Majorana fermions. △ Less

Submitted 12 September, 2020; v1 submitted 3 June, 2019; originally announced June 2019.

Comments: New text and results. 19 pages, 13 figures, supplementary material

Journal ref: npj Quantum Inf. 7, 91 (2021)

Determining the depairing current in superconducting nanowire single-photon detectors

Authors: S. Frasca, B. Korzh, M. Colangelo, D. Zhu, A. E. Lita, J. P. Allmaras, E. E. Wollman, V. B. Verma, A. E. Dane, E. Ramirez, A. D. Beyer, S. W. Nam, A. G. Kozorezov, M. D. Shaw, K. K. Berggren

Abstract: We estimate the depairing current of superconducting nanowire single photon detectors (SNSPDs) by studying the dependence of the nanowires kinetic inductance on their bias current. The kinetic inductance is determined by measuring the resonance frequency of resonator style nanowire coplanar waveguides both in transmission and reflection configurations. Bias current dependent shifts in the measured… ▽ More We estimate the depairing current of superconducting nanowire single photon detectors (SNSPDs) by studying the dependence of the nanowires kinetic inductance on their bias current. The kinetic inductance is determined by measuring the resonance frequency of resonator style nanowire coplanar waveguides both in transmission and reflection configurations. Bias current dependent shifts in the measured resonant frequency correspond to the change in the kinetic inductance, which can be compared with theoretical predictions. We demonstrate that the fast relaxation model described in the literature accurately matches our experimental data and provides a valuable tool for direct determination of the depairing current. Accurate and direct measurement of the depairing current is critical for nanowire quality analysis, as well as modeling efforts aimed at understanding the detection mechanism in SNSPDs. △ Less

Submitted 18 April, 2019; originally announced April 2019.

Journal ref: Phys. Rev. B 100, 054520 (2019)

An ultrahigh-impedance superconducting thermal switch for interfacing superconductors to semiconductors and optoelectronics

Authors: A. N. McCaughan, V. B. Verma, S. Buckley, J. P. Allmaras, A. G. Kozorezov, A. N. Tait, S. W. Nam, J. M. Shainline

Abstract: A number of current approaches to quantum and neuromorphic computing use superconductors as the basis of their platform or as a measurement component, and will need to operate at cryogenic temperatures. Semiconductor systems are typically proposed as a top-level control in these architectures, with low-temperature passive components and intermediary superconducting electronics acting as the direct… ▽ More A number of current approaches to quantum and neuromorphic computing use superconductors as the basis of their platform or as a measurement component, and will need to operate at cryogenic temperatures. Semiconductor systems are typically proposed as a top-level control in these architectures, with low-temperature passive components and intermediary superconducting electronics acting as the direct interface to the lowest-temperature stages. The architectures, therefore, require a low-power superconductor-semiconductor interface, which is not currently available. Here we report a superconducting switch that is capable of translating low-voltage superconducting inputs directly into semiconductor-compatible (above 1,000 mV) outputs at kelvin-scale temperatures (1 K or 4 K). To illustrate the capabilities in interfacing superconductors and semiconductors, we use it to drive a light-emitting diode (LED) in a photonic integrated circuit, generating photons at 1 K from a low-voltage input and detecting them with an on-chip superconducting single-photon detector. We also characterize our device's timing response (less than 300 ps turn-on, 15 ns turn-off), output impedance (greater than 1 MΩ), and energy requirements (0.18 fJ/um^2, 3.24 mV/nW). △ Less

Submitted 30 September, 2019; v1 submitted 25 March, 2019; originally announced March 2019.

Integrated transition edge sensors on lithium niobate waveguides

Authors: Jan Philipp Höpker, Thomas Gerrits, Adriana Lita, Stephan Krapick, Harald Herrmann, Raimund Ricken, Viktor Quiring, Richard Mirin, Sae Woo Nam, Christine Silberhorn, Tim J. Bartley

Abstract: We show the proof-of-principle detection of light at 1550 nm coupled evanescently from a titanium in-diffused lithium niobate waveguide to a superconducting transition edge sensor. The coupling efficiency strongly depends on the polarization, the overlap between the evanescent field, and the detector structure. We experimentally demonstrate polarization sensitivity of this coupling as well as phot… ▽ More We show the proof-of-principle detection of light at 1550 nm coupled evanescently from a titanium in-diffused lithium niobate waveguide to a superconducting transition edge sensor. The coupling efficiency strongly depends on the polarization, the overlap between the evanescent field, and the detector structure. We experimentally demonstrate polarization sensitivity of this coupling as well as photon-number resolution of the integrated detector. The combination of transition edge sensors and lithium niobate waveguides can open the field for a variety of new quantum optics experiments. △ Less

Submitted 20 December, 2018; originally announced December 2018.

Comments: 4 pages, 5 figures

Journal ref: APL Photonics 4, 056103 (2019)

Demonstrating sub-3 ps temporal resolution in a superconducting nanowire single-photon detector

Authors: B. A. Korzh, Q-Y. Zhao, S. Frasca, J. P. Allmaras, T. M. Autry, E. A. Bersin, M. Colangelo, G. M. Crouch, A. E. Dane, T. Gerrits, F. Marsili, G. Moody, E. Ramirez, J. D. Rezac, M. J. Stevens, E. E. Wollman, D. Zhu, P. D. Hale, K. L. Silverman, R. P. Mirin, S. W. Nam, M. D. Shaw, K. K. Berggren

Abstract: Improving the temporal resolution of single photon detectors has an impact on many applications, such as increased data rates and transmission distances for both classical and quantum optical communication systems, higher spatial resolution in laser ranging and observation of shorter-lived fluorophores in biomedical imaging. In recent years, superconducting nanowire single-photon detectors (SNSPDs… ▽ More Improving the temporal resolution of single photon detectors has an impact on many applications, such as increased data rates and transmission distances for both classical and quantum optical communication systems, higher spatial resolution in laser ranging and observation of shorter-lived fluorophores in biomedical imaging. In recent years, superconducting nanowire single-photon detectors (SNSPDs) have emerged as the highest efficiency time-resolving single-photon counting detectors available in the near infrared. As the detection mechanism in SNSPDs occurs on picosecond time scales, SNSPDs have been demonstrated with exquisite temporal resolution below 15 ps. We reduce this value to 2.7$\pm$0.2 ps at 400 nm and 4.6$\pm$0.2 ps at 1550 nm, using a specialized niobium nitride (NbN) SNSPD. The observed photon-energy dependence of the temporal resolution and detection latency suggests that intrinsic effects make a significant contribution. △ Less

Submitted 18 April, 2018; originally announced April 2018.

Comments: 25 pages, 9 figures

Superconducting fluctuations and characteristic time scales in amorphous WSi

Authors: Xiaofu Zhang, Adriana E. Lita, Mariia Sidorova, Varun B. Verma, Qiang Wang, Sae Woo Nam, Alexej Semenov, Andreas Schilling

Abstract: We study magnitudes and temperature dependences of the electron-electron and electron-phonon interaction times which play the dominant role in the formation and relaxation of photon induced hotspot in two dimensional amorphous WSi films. The time constants are obtained through magnetoconductance measurements in perpendicular magnetic field in the superconducting fluctuation regime and through time… ▽ More We study magnitudes and temperature dependences of the electron-electron and electron-phonon interaction times which play the dominant role in the formation and relaxation of photon induced hotspot in two dimensional amorphous WSi films. The time constants are obtained through magnetoconductance measurements in perpendicular magnetic field in the superconducting fluctuation regime and through time-resolved photoresponse to optical pulses. The excess magnetoconductivity is interpreted in terms of the weak-localization effect and superconducting fluctuations. Aslamazov-Larkin, and Maki-Thompson superconducting fluctuation alone fail to reproduce the magnetic field dependence in the relatively high magnetic field range when the temperature is rather close to Tc because the suppression of the electronic density of states due to the formation of short lifetime Cooper pairs needs to be considered. The time scale τ_i of inelastic scattering is ascribed to a combination of electron-electron (τ_(e-e)) and electron-phonon (τ_(e-ph)) interaction times, and a characteristic electron-fluctuation time (τ_(e-fl)), which makes it possible to extract their magnitudes and temperature dependences from the measured τ_i. The ratio of phonon-electron (τ_(ph-e)) and electron-phonon interaction times is obtained via measurements of the optical photoresponse of WSi microbridges. Relatively large τ_(e-ph)/τ_(ph-e) and τ_(e-ph)/τ_(e-e) ratios ensure that in WSi the photon energy is more efficiently confined in the electron subsystem than in other materials commonly used in the technology of superconducting nanowire single-photon detectors (SNSPDs). We discuss the impact of interaction times on the hotspot dynamics and compare relevant metrics of SNSPDs from different materials. △ Less

Submitted 13 December, 2017; originally announced December 2017.

Journal ref: Phys. Rev. B 97, 174502 (2018)

Direct observation of nanofabrication influence on the optical properties of single self-assembled InAs/GaAs quantum dots

Authors: Jin Liu, Kumarasiri Konthasinghe, Marcelo Davanco, John Lawall, Vikas Anant, Varun Verma, Richard Mirin, Sae Woo Nam, Jin Dong Song, Ben Ma, Ze Sheng Chen, Hai Qiao Ni, Zhi Chuan Niu, Kartik Srinivasan

Abstract: Single self-assembled InAs/GaAs quantum dots are a promising solid-state quantum technology, with which vacuum Rabi splitting, single-photon-level nonlinearities, and bright, pure, and indistinguishable single-photon generation having been demonstrated. For such achievements, nanofabrication is used to create structures in which the quantum dot preferentially interacts with strongly-confined optic… ▽ More Single self-assembled InAs/GaAs quantum dots are a promising solid-state quantum technology, with which vacuum Rabi splitting, single-photon-level nonlinearities, and bright, pure, and indistinguishable single-photon generation having been demonstrated. For such achievements, nanofabrication is used to create structures in which the quantum dot preferentially interacts with strongly-confined optical modes. An open question is the extent to which such nanofabrication may also have an adverse influence, through the creation of traps and surface states that could induce blinking, spectral diffusion, and dephasing. Here, we use photoluminescence imaging to locate the positions of single InAs/GaAs quantum dots with respect to alignment marks with < 5 nm uncertainty, allowing us to measure their behavior before and after fabrication. We track the quantum dot emission linewidth and photon statistics as a function of distance from an etched surface, and find that the linewidth is significantly broadened (up to several GHz) for etched surfaces within a couple hundred nanometers of the quantum dot. However, we do not observe appreciable reduction of the quantum dot radiative efficiency due to blinking. We also show that atomic layer deposition can stabilize spectral diffusion of the quantum dot emission, and partially recover its linewidth. △ Less

Submitted 26 October, 2017; originally announced October 2017.

Comments: 11 pages, 8 figures

Journal ref: Phys. Rev. Applied 9, 064019 (2018)

Towards integrated superconducting detectors on lithium niobate waveguides

Authors: Jan Philipp Höpker, Moritz Bartnick, Evan Meyer-Scott, Frederik Thiele, Stephan Krapick, Nicola Montaut, Matteo Santandrea, Harald Herrmann, Sebastian Lengeling, Raimund Ricken, Viktor Quiring, Torsten Meier, Adriana Lita, Varun Verma, Thomas Gerrits, Sae Woo Nam, Christine Silberhorn, Tim J. Bartley

Abstract: Superconducting detectors are now well-established tools for low-light optics, and in particular quantum optics, boasting high-efficiency, fast response and low noise. Similarly, lithium niobate is an important platform for integrated optics given its high second-order nonlinearity, used for high-speed electro-optic modulation and polarization conversion, as well as frequency conversion and source… ▽ More Superconducting detectors are now well-established tools for low-light optics, and in particular quantum optics, boasting high-efficiency, fast response and low noise. Similarly, lithium niobate is an important platform for integrated optics given its high second-order nonlinearity, used for high-speed electro-optic modulation and polarization conversion, as well as frequency conversion and sources of quantum light. Combining these technologies addresses the requirements for a single platform capable of generating, manipulating and measuring quantum light in many degrees of freedom, in a compact and potentially scalable manner. We will report on progress integrating tungsten transition-edge sensors (TESs) and amorphous tungsten silicide superconducting nanowire single-photon detectors (SNSPDs) on titanium in-diffused lithium niobate waveguides. The travelling-wave design couples the evanescent field from the waveguides into the superconducting absorber. We will report on simulations and measurements of the absorption, which we can characterize at room temperature prior to cooling down the devices. Independently, we show how the detectors respond to flood illumination, normally incident on the devices, demonstrating their functionality. △ Less

Submitted 18 August, 2017; originally announced August 2017.

Comments: 7 pages, 4 figures

UV superconducting nanowire single-photon detectors with high efficiency, low noise, and 4 K operating temperature

Authors: Emma E. Wollman, Varun B. Verma, Andrew D. Beyer, Ryan M. Briggs, Francesco Marsili, Jason P. Allmaras, Adriana E. Lita, Richard P. Mirin, Sae Woo Nam, Matthew D. Shaw

Abstract: For photon-counting applications at ultraviolet wavelengths, there are currently no detectors that combine high efficiency (> 50%), sub-nanosecond timing resolution, and sub-Hz dark count rates. Superconducting nanowire single-photon detectors (SNSPDs) have seen success over the past decade for photon-counting applications in the near-infrared, but little work has been done to optimize SNSPDs for… ▽ More For photon-counting applications at ultraviolet wavelengths, there are currently no detectors that combine high efficiency (> 50%), sub-nanosecond timing resolution, and sub-Hz dark count rates. Superconducting nanowire single-photon detectors (SNSPDs) have seen success over the past decade for photon-counting applications in the near-infrared, but little work has been done to optimize SNSPDs for wavelengths below 400 nm. Here, we describe the design, fabrication, and characterization of UV SNSPDs operating at wavelengths between 250 and 370 nm. The detectors have active areas up to 56 $μ$m in diameter, 70 - 80% efficiency, timing resolution down to 60 ps FWHM, blindness to visible and infrared photons, and dark count rates of ~ 0.25 counts/hr for a 56 $μ$m diameter pixel. By using the amorphous superconductor MoSi, these UV SNSPDs are also able to operate at temperatures up to 4.2 K. These performance metrics make UV SNSPDs ideal for applications in trapped-ion quantum information processing, lidar studies of the upper atmosphere, UV fluorescent-lifetime imaging microscopy, and photon-starved UV astronomy. △ Less

Submitted 11 August, 2017; originally announced August 2017.

Comments: 9 pages, 6 figures

Modeling Bloch Oscillations in Nanoscale Josephson Junctions

Authors: Heli Vora, R. L. Kautz, S. W. Nam, J. Aumentado

Abstract: Bloch oscillations in nanoscale Josephson junctions with a Coulomb charging energy comparable to the Josephson coupling energy are explored within the context of a model previously considered by Geigenmüller and Schön that includes Zener tunneling and treats quasiparticle tunneling as an explicit shot-noise process. The dynamics of the junction quasicharge are investigated numerically using both M… ▽ More Bloch oscillations in nanoscale Josephson junctions with a Coulomb charging energy comparable to the Josephson coupling energy are explored within the context of a model previously considered by Geigenmüller and Schön that includes Zener tunneling and treats quasiparticle tunneling as an explicit shot-noise process. The dynamics of the junction quasicharge are investigated numerically using both Monte Carlo and ensemble approaches to calculate voltage--current characteristics in the presence of microwaves. We examine in detail the origin of harmonic and subharmonic Bloch steps at dc biases $I=(n/m)2ef$ induced by microwaves of frequency $f$ and consider the optimum parameters for the observation of harmonic ($m=1$) steps. We also demonstrate that the GS model allows a detailed semi-quantitative fit to experimental voltage--current characteristics previously obtained at the Chalmers University of Technology, confirming and strengthening the interpretation of the observed microwave-induced steps in terms of Bloch oscillations. △ Less

Submitted 20 March, 2017; originally announced March 2017.

Journal ref: Phys. Rev. B 96, 054505 (2017)

Fano fluctuations in superconducting nanowire single-photon detectors

Authors: A. G. Kozorezov, C. Lambert, F. Marsili, M. J. Stevens, V. B. Verma, J. P. Allmaras, M. D. Shaw, R. P. Mirin, Sae Woo Nam

Abstract: Because of their universal nature, Fano fluctuations are expected to influence the response of superconducting nanowire single-photon detectors (SNSPDs). We predict that photon counting rate ($PCR$) as a function of bias current ($I_B$) in SNSPDs is described by an integral over a transverse coordinate-dependent complementary error function. The latter describes smearing of local responses due to… ▽ More Because of their universal nature, Fano fluctuations are expected to influence the response of superconducting nanowire single-photon detectors (SNSPDs). We predict that photon counting rate ($PCR$) as a function of bias current ($I_B$) in SNSPDs is described by an integral over a transverse coordinate-dependent complementary error function. The latter describes smearing of local responses due to Fano fluctuations of the amount of energy deposited into electronic system. The finite width, $σ$, of the $PCR$ vs $I_B$ arises from fluctuations in the energy partition between quasiparticles and phonons during the energy down-conversion cascade. In narrow-nanowire SNSPDs the local responses are uniform, and the effect of Fano-fluctuations on $σ$ is dominant. In wide-nanowire SNSPDs with strong coordinate dependence of local responses due to vortex-antivortex unbinding and vortex entry from edges, Fano-fluctuations smear singularities imprinted by vorticity on the transition part of $PCR$ curve. We demonstrate good agreement between theory and experiments for a series of bath temperatures and photon energies in narrow-wire WSi SNSPDs. The time-resolved hotspot relaxation curves predicted by Fano fluctuations match the Lorentzian shapes observed in experiments over the whole range of bias currents investigated except for their tails. △ Less

Submitted 9 February, 2017; originally announced February 2017.

Comments: 12 pages, 8 figures

Journal ref: Phys. Rev. B 96, 054507 (2017)

UV-sensitive superconducting nanowire single photon detectors for integration in an ion trap

Authors: D. H. Slichter, V. B. Verma, D. Leibfried, R. P. Mirin, S. W. Nam, D. J. Wineland

Abstract: We demonstrate superconducting nanowire single photon detectors with 76 +/- 4 % system detection efficiency at a wavelength of 315 nm and an operating temperature of 3.2 K, with a background count rate below 1 count per second at saturated detection efficiency. We propose integrating these detectors into planar surface electrode radio-frequency Paul traps for use in trapped ion quantum information… ▽ More We demonstrate superconducting nanowire single photon detectors with 76 +/- 4 % system detection efficiency at a wavelength of 315 nm and an operating temperature of 3.2 K, with a background count rate below 1 count per second at saturated detection efficiency. We propose integrating these detectors into planar surface electrode radio-frequency Paul traps for use in trapped ion quantum information processing. We operate detectors integrated into test ion trap structures at 3.8 K both with and without typical radio-frequency trapping electric fields. The trapping fields reduce system detection efficiency by 9 %, but do not increase background count rates. △ Less

Submitted 10 April, 2017; v1 submitted 29 November, 2016; originally announced November 2016.

Comments: 16 pages, 7 figures

Journal ref: Opt. Express 25, 8705-8720 (2017)

Efficient fiber-coupled single-photon source based on quantum dots in a photonic-crystal waveguide

Authors: Raphaël S. Daveau, Krishna C. Balram, Tommaso Pregnolato, Jin Liu, Eun H. Lee, Jin D. Song, Varun Verma, Richard Mirin, Sae Woo Nam, Leonardo Midolo, Søren Stobbe, Kartik Srinivasan, Peter Lodahl

Abstract: Many photonic quantum information processing applications would benefit from a high brightness, fiber-coupled source of triggered single photons. Here, we present a fiber-coupled photonic-crystal waveguide single-photon source relying on evanescent coupling of the light field from a tapered out-coupler to an optical fiber. A two-step approach is taken where the performance of the tapered out-coupl… ▽ More Many photonic quantum information processing applications would benefit from a high brightness, fiber-coupled source of triggered single photons. Here, we present a fiber-coupled photonic-crystal waveguide single-photon source relying on evanescent coupling of the light field from a tapered out-coupler to an optical fiber. A two-step approach is taken where the performance of the tapered out-coupler is recorded first on an independent device containing an on-chip reflector. Reflection measurements establish that the chip-to-fiber coupling efficiency exceeds 80 %. The detailed characterization of a high-efficiency photonic-crystal waveguide extended with a tapered out-coupling section is then performed. The corresponding overall single-photon source efficiency is 10.9 % $\pm$ 2.3 %, which quantifies the success probability to prepare an exciton in the quantum dot, couple it out as a photon in the waveguide, and subsequently transfer it to the fiber. The applied out-coupling method is robust, stable over time, and broadband over several tens of nanometers, which makes it a highly promising pathway to increase the efficiency and reliability of planar chip-based single-photon sources. △ Less

Submitted 27 October, 2016; originally announced October 2016.

Comments: 9 pages, 3 figures

Superconducting optoelectronic circuits for neuromorphic computing

Authors: Jeffrey M. Shainline, Sonia M. Buckley, Richard P. Mirin, Sae Woo Nam

Abstract: Neural networks have proven effective for solving many difficult computational problems. Implementing complex neural networks in software is very computationally expensive. To explore the limits of information processing, it will be necessary to implement new hardware platforms with large numbers of neurons, each with a large number of connections to other neurons. Here we propose a hybrid semicon… ▽ More Neural networks have proven effective for solving many difficult computational problems. Implementing complex neural networks in software is very computationally expensive. To explore the limits of information processing, it will be necessary to implement new hardware platforms with large numbers of neurons, each with a large number of connections to other neurons. Here we propose a hybrid semiconductor-superconductor hardware platform for the implementation of neural networks and large-scale neuromorphic computing. The platform combines semiconducting few-photon light-emitting diodes with superconducting-nanowire single-photon detectors to behave as spiking neurons. These processing units are connected via a network of optical waveguides, and variable weights of connection can be implemented using several approaches. The use of light as a signaling mechanism overcomes fanout and parasitic constraints on electrical signals while simultaneously introducing physical degrees of freedom which can be employed for computation. The use of supercurrents achieves the low power density necessary to scale to systems with enormous entropy. The proposed processing units can operate at speeds of at least $20$ MHz with fully asynchronous activity, light-speed-limited latency, and power densities on the order of 1 mW/cm$^2$ for neurons with 700 connections operating at full speed at 2 K. The processing units achieve an energy efficiency of $\approx 20$ aJ per synapse event. By leveraging multilayer photonics with deposited waveguides and superconductors with feature sizes $>$ 100 nm, this approach could scale to systems with massive interconnectivity and complexity for advanced computing as well as explorations of information processing capacity in systems with an enormous number of information-bearing microstates. △ Less

Submitted 10 November, 2016; v1 submitted 30 September, 2016; originally announced October 2016.

Comments: 34 pages, 22 figures

Experimental investigation of the detection mechanism in WSi nanowire superconducting single photon detectors

Authors: Rosalinda Gaudio, Jelmer J. Renema, Zili Zhou, Varun B. Verma, Adriana E. Lita, Jeffrey Shainline, Martin J. Stevens, Richard P. Mirin, Sae Woo Nam, Martin P. van Exter, Michiel J. A. de Dood, Andrea Fiore

Abstract: We use quantum detector tomography to investigate the detection mechanism in WSi nanowire superconducting single photon detectors (SSPDs). To this purpose, we fabricated a 250nm wide and 250nm long WSi nanowire and measured its response to impinging photons with wavelengths ranging from $λ$ = 900 nm to $λ$ = 1650 nm. Tomographic measurements show that the detector response depends on the total exc… ▽ More We use quantum detector tomography to investigate the detection mechanism in WSi nanowire superconducting single photon detectors (SSPDs). To this purpose, we fabricated a 250nm wide and 250nm long WSi nanowire and measured its response to impinging photons with wavelengths ranging from $λ$ = 900 nm to $λ$ = 1650 nm. Tomographic measurements show that the detector response depends on the total excitation energy only. Moreover, for energies Et > 0.8eV the current energy relation is linear, similar to what was observed in NbN nanowires, whereas the current-energy relation deviates from linear behaviour for total energies below 0.8eV. △ Less

Submitted 7 June, 2016; v1 submitted 24 February, 2016; originally announced February 2016.

Hotspot Relaxation Dynamics in a Current Carrying Superconductor

Authors: F. Marsili, M. J. Stevens, A. Kozorezov, V. B. Verma, Colin Lambert, J. A. Stern, R. Horansky, S. Dyer, S. Duff, D. P. Pappas, A. Lita, M. D. Shaw, R. P. Mirin, S. W. Nam

Abstract: We experimentally studied the dynamics of optically excited hotspots in current carrying WSi superconducting nanowires as a function of bias current, bath temperature and excitation wavelength. We discovered that: (1) the hotspot relaxation is a factor of ~ 4 slower in WSi than in NbN; (2) the hotspot relaxation time depends on bias current, and (3) the current dependence of the hotspot relaxation… ▽ More We experimentally studied the dynamics of optically excited hotspots in current carrying WSi superconducting nanowires as a function of bias current, bath temperature and excitation wavelength. We discovered that: (1) the hotspot relaxation is a factor of ~ 4 slower in WSi than in NbN; (2) the hotspot relaxation time depends on bias current, and (3) the current dependence of the hotspot relaxation time changes with temperature and wavelength. We explained all of these effects with a model based on quasi particle recombination. △ Less

Submitted 9 June, 2015; originally announced June 2015.

Journal ref: Phys. Rev. B 93, 094518 (2016)

Quantum storage of entangled telecom-wavelength photons in an erbium-doped optical fibre

Authors: Erhan Saglamyurek, Jeongwan Jin, Varun B. Verma, Matthew D. Shaw, Francesco Marsili, Sae Woo Nam, Daniel Oblak, Wolfgang Tittel

Abstract: The realization of a future quantum Internet requires processing and storing quantum information at local nodes, and interconnecting distant nodes using free-space and fibre-optic links. Quantum memories for light are key elements of such quantum networks. However, to date, neither an atomic quantum memory for non-classical states of light operating at a wavelength compatible with standard telecom… ▽ More The realization of a future quantum Internet requires processing and storing quantum information at local nodes, and interconnecting distant nodes using free-space and fibre-optic links. Quantum memories for light are key elements of such quantum networks. However, to date, neither an atomic quantum memory for non-classical states of light operating at a wavelength compatible with standard telecom fibre infrastructure, nor a fibre-based implementation of a quantum memory has been reported. Here we demonstrate the storage and faithful recall of the state of a 1532 nm wavelength photon, entangled with a 795 nm photon, in an ensemble of cryogenically cooled erbium ions doped into a 20 meter-long silicate fibre using a photon-echo quantum memory protocol. Despite its currently limited efficiency and storage time, our broadband light-matter interface brings fibre-based quantum networks one step closer to reality. Furthermore, it facilitates novel tests of light-matter interaction and collective atomic effects in unconventional materials. △ Less

Submitted 13 January, 2015; v1 submitted 2 September, 2014; originally announced September 2014.

Comments: 6 pages, 3 Figures + Supplementary Information. The problem with the order of the references is fixed. appears in Nature Photonics (2015)

Journal ref: Nature Photonics 9, 83-87, 2015

High-efficiency WSi superconducting nanowire single-photon detectors operating at 2.5 K

Authors: V. B. Verma, B. Korzh, F. Bussières, R. D. Horansky, A. E. Lita, F. Marsili, M. D. Shaw, H. Zbinden, R. P. Mirin, S. W. Nam

Abstract: We investigate the operation of WSi superconducting nanowire single-photon detectors (SNSPDs) at 2.5 K, a temperature which is ~ 70 % of the superconducting transition temperature (TC) of 3.4 K. We demonstrate saturation of the system detection efficiency at 78 +- 2 % with a jitter of 191 ps. We find that the jitter at 2.5 K is limited by the noise of the readout, and can be improved through the u… ▽ More We investigate the operation of WSi superconducting nanowire single-photon detectors (SNSPDs) at 2.5 K, a temperature which is ~ 70 % of the superconducting transition temperature (TC) of 3.4 K. We demonstrate saturation of the system detection efficiency at 78 +- 2 % with a jitter of 191 ps. We find that the jitter at 2.5 K is limited by the noise of the readout, and can be improved through the use of cryogenic amplifiers. Operation of SNSPDs with high efficiency at temperatures very close to TC appears to be a unique property of amorphous WSi. △ Less

Submitted 6 June, 2014; originally announced June 2014.

Superconducting nanowire single photon detectors fabricated from an amorphous Mo0.75Ge0.25 thin film

Authors: V. B. Verma, A. E. Lita, M. R. Vissers, F. Marsili, D. P. Pappas, R. P. Mirin, S. W. Nam

Abstract: We present the characteristics of superconducting nanowire single photon detectors (SNSPDs) fabricated from amorphous Mo0.75Ge0.25 thin-films. Fabricated devices show a saturation of the internal detection efficiency at temperatures below 1 K, with system dark count rates below 500 counts per second. Operation in a Gifford-McMahon (GM) cryocooler at 2.5 K is possible with system detection efficien… ▽ More We present the characteristics of superconducting nanowire single photon detectors (SNSPDs) fabricated from amorphous Mo0.75Ge0.25 thin-films. Fabricated devices show a saturation of the internal detection efficiency at temperatures below 1 K, with system dark count rates below 500 counts per second. Operation in a Gifford-McMahon (GM) cryocooler at 2.5 K is possible with system detection efficiencies (SDE) exceeding 20% for SNSPDs which have not been optimized for high detection efficiency. △ Less

Submitted 18 February, 2014; originally announced February 2014.

Detecting Single Infrared Photons with 93% System Efficiency

Authors: F. Marsili, V. B. Verma, J. A. Stern, S. Harrington, A. E. Lita, T. Gerrits, I. Vayshenker, B. Baek, M. D. Shaw, R. P. Mirin, S. W. Nam

Abstract: Single-photon detectors (SPDs) at near infrared wavelengths with high system detection efficiency (> 90%), low dark count rate (< 1 counts per second, cps), low timing jitter (< 100 ps), and short reset time (< 100 ns) would enable landmark experiments in a variety of fields. Although some of the existing approaches to single-photon detection fulfill one or two of the above specifications, to date… ▽ More Single-photon detectors (SPDs) at near infrared wavelengths with high system detection efficiency (> 90%), low dark count rate (< 1 counts per second, cps), low timing jitter (< 100 ps), and short reset time (< 100 ns) would enable landmark experiments in a variety of fields. Although some of the existing approaches to single-photon detection fulfill one or two of the above specifications, to date no detector has met all of the specifications simultaneously. Here we report on a fiber-coupled single-photon-detection system employing superconducting nanowire single photon detectors (SNSPDs) that closely approaches the ideal performance of SPDs. Our detector system has a system detection efficiency (SDE), including optical coupling losses, greater than 90% in the wavelength range λ= 1520-1610 nm; device dark count rate (measured with the device shielded from room-temperature blackbody radiation) of ~ 0.01 cps; timing jitter of ~ 150 ps FWHM; and reset time of 40 ns. △ Less

Submitted 25 September, 2012; originally announced September 2012.

A titanium-nitride near-infrared kinetic inductance photon-counting detector and its anomalous electrodynamics

Authors: J. Gao, M. R. Visser, M. O. Sandberg, F. C. S. da Silva, S. W. Nam, D. P. Pappas, K. D. Irwin, D. S. Wisbey, E. Langman, S. R. Meeker, B. A. Mazin, H. G. Leduc, J. Zmuidzinas

Abstract: We demonstrate single-photon counting at 1550 nm with titanium-nitride (TiN) microwave kinetic inductance detectors. Energy resolution of 0.4 eV and arrival-time resolution of 1.2 microseconds are achieved. 0-, 1-, 2-photon events are resolved and shown to follow Poisson statistics. We find that the temperature-dependent frequency shift deviates from the Mattis-Bardeen theory, and the dissipation… ▽ More We demonstrate single-photon counting at 1550 nm with titanium-nitride (TiN) microwave kinetic inductance detectors. Energy resolution of 0.4 eV and arrival-time resolution of 1.2 microseconds are achieved. 0-, 1-, 2-photon events are resolved and shown to follow Poisson statistics. We find that the temperature-dependent frequency shift deviates from the Mattis-Bardeen theory, and the dissipation response shows a shorter decay time than the frequency response at low temperatures. We suggest that the observed anomalous electrodynamics may be related to quasiparticle traps or subgap states in the disordered TiN films. Finally, the electron density-of-states is derived from the pulse response. △ Less

Submitted 3 August, 2012; originally announced August 2012.

Comments: 4 pages, 3 figures