arXiv subjects

Marco Colangelo

Publications and source records attributed to Marco Colangelo.

At least 37 records · Page 2Linked to original sources

arXiv2022

A Nanocryotron Memory and Logic Family

The development of superconducting electronics based on nanocryotrons has been limited so far to few-device circuits, in part due to the lack of standard and robust logic cells. Here, we introduce and experimentally demonstrate designs for a set of nanocryotron-based building blocks that can be configured and combined to implement memory and logic functions. The devices were fabricated by patterning a single superconducting layer of niobium nitride and measured in liquid helium on a wide range of operating points. The tests show $10^{-4}$ bit error rates with above $20\,\%$ margins up to $50\,$MHz and the possibility of operating under the effect of a perpendicular $36\,$mT magnetic field, with $30\,\%$ margins at $10\,$MHz. Additionally, we designed and measured an equivalent delay flip-flop made of two memory cells to show the possibility of combining multiple building blocks to make larger circuits. These blocks may constitute a solid foundation for the development of nanocryotron logic circuits and finite-state machines with potential applications in the integrated processing and control of superconducting nanowire single-photon detectors.

physics.app-ph↗

arXiv2022

Reversible Tuning of Superconductivity in Ion-Gated NbN Ultrathin Films by Self-Encapsulation with a High-$κ$ Dielectric Layer

Ionic gating is a powerful technique for tuning the physical properties of a material via electric field-induced charge doping, but is prone to introduce extrinsic disorder and undesired electrochemical modifications in the gated material beyond pure electrostatics. Conversely, reversible, volatile and electrostatic modulation is pivotal in the reliable design and operation of novel device concepts enabled by the ultrahigh induced charge densities attainable via ionic gating. Here we demonstrate a simple and effective method to achieve reversible and volatile gating of surface-sensitive ultrathin niobium nitride films via controlled oxidation of their surface. The resulting niobium oxide encapsulation layer exhibits a capacitance comparable to that of non-encapsulated ionic transistors, withstands gate voltages beyond the electrochemical stability window of the gate electrolyte, and enables a fully-reversible tunability of both the normal-state resistivity and the superconducting transition temperature of the encapsulated films. Our approach should be transferable to other materials and device geometries where more standard encapsulation techniques are not readily applicable.

cond-mat.supr-con↗

arXiv2022

New Constraints on Dark Photon Dark Matter with Superconducting Nanowire Detectors in an Optical Haloscope

Uncovering the nature of dark matter is one of the most important goals of particle physics. Light bosonic particles, such as the dark photon, are well-motivated candidates: they are generally long-lived, weakly-interacting, and naturally produced in the early universe. In this work, we report on LAMPOST (Light $A'$ Multilayer Periodic Optical SNSPD Target), a proof-of-concept experiment searching for dark photon dark matter in the eV mass range, via coherent absorption in a multi-layer dielectric haloscope. Using a superconducting nanowire single-photon detector (SNSPD), we achieve efficient photon detection with a dark count rate (DCR) of $\sim 6\times10^{-6}$ counts/s. We find no evidence for dark photon dark matter in the mass range of $\sim 0.7$-$0.8$ eV with kinetic mixing $ε\gtrsim 10^{-12}$, improving existing limits in $ε$ by up to a factor of two. With future improvements to SNSPDs, our architecture could probe significant new parameter space for dark photon and axion dark matter in the meV to 10 eV mass range.

hep-ex↗

arXiv2022

Electrical Control of Surface Acoustic Waves

Acoustic waves at microwave frequencies have been widely used in wireless communication and recently emerged as versatile information carriers in quantum applications. However, most acoustic devices are passive components, and dynamic control of acoustic waves in a low-loss and scalable manner remains an outstanding challenge, which hinders the development of phononic integrated circuits. Here we demonstrate electrical control of traveling acoustic waves on an integrated lithium niobate platform at both room and millikelvin temperatures. We modulate the phase and amplitude of the acoustic waves and demonstrate an acoustic frequency shifter by serrodyne phase modulation. Furthermore, we show reconfigurable nonreciprocal modulation by tailoring the phase matching between acoustic and quasi-traveling electric fields. Our scalable electro-acoustic platform comprises the fundamental elements for arbitrary acoustic signal processing and manipulation of phononic quantum information.

physics.app-ph↗

arXiv2021

50 Ohm Transmission Lines with Extreme Wavelength Compression Based on Superconducting Nanowires on High-Permittivity Substrates

We demonstrate impedance-matched low-loss transmission lines with a signal wavelength more than 150 times smaller than the free space wavelength using superconducting nanowires on high permittivity substrates. A niobium nitride thin film is patterned in a coplanar waveguide (CPW) transmission line geometry on a bilayer substrate consisting of 100 nm of epitaxial strontium titanate on high-resitivity silicon. The use of strontium titanate on silicon enables wafer-scale fabrication and maximizes process compatibility. It also makes it possible to realize a $50$ $Ω$ characteristic impedance across a wide range of CPW widths, from the nanoscale to the macroscale. We fabricated and characterized an approximately $50$ $Ω$ CPW device with two half-wave stub resonators. Comparing the measured transmission coefficient to numerical simulations, we determine that the strontium titanate film has a dielectric constant of $1.1 \times 10^3$ and a loss tangent of not more than 0.009. To facilitate the design of distributed microwave devices based on this type of material system, we describe an analytical model of the CPW properties that gives good agreement with both measurements and simulations.

cond-mat.supr-con↗

arXiv2021

Impedance-matched differential superconducting nanowire detectors

Superconducting nanowire single-photon detectors (SNSPDs) are the highest performing photon-counting technology in the near-infrared (NIR). Due to delay-line effects, large area SNSPDs typically trade-off timing resolution and detection efficiency. Here, we introduce a detector design based on transmission line engineering and differential readout for device-level signal conditioning, enabling a high system detection efficiency and a low detector jitter, simultaneously. To make our differential detectors compatible with single-ended time taggers, we also engineer analog differential-to-single-ended readout electronics, with minimal impact on the system timing resolution. Our niobium nitride differential SNSPDs achieve $47.3\,\% \pm 2.4\,\%$ system detection efficiency and sub-$10\,\mathrm{ps}$ system jitter at $775\,\mathrm{nm}$, while at $1550\,\mathrm{nm}$ they achieve $71.1\,\% \pm 3.7\,\%$ system detection efficiency and $13.1\,\mathrm{ps} \pm 0.4\,\mathrm{ps}$ system jitter. These detectors also achieve sub-100 ps timing response at one one-hundredth maximum level, $30.7\,\mathrm{ps} \pm 0.4\,\mathrm{ps}$ at $775\,\mathrm{nm}$ and $47.6\,\mathrm{ps} \pm 0.4\,\mathrm{ps}$ at $1550\,\mathrm{nm}$, enabling time-correlated single-photon counting with high dynamic range response functions. Furthermore, thanks to the differential impedance-matched design, our detectors exhibit delay-line imaging capabilities and photon-number resolution. The properties and high-performance metrics achieved by our system make it a versatile photon-detection solution for many scientific applications.

physics.app-ph↗

arXiv2021

Self-Heating Hotspots in Superconducting Nanowires Cooled by Phonon Black-Body Radiation

Controlling thermal transport is important for a range of devices and technologies, from phase change memories to next-generation electronics. This is especially true in nano-scale devices where thermal transport is altered by the influence of surfaces and changes in dimensionality. In superconducting nanowire single-photon detectors, the thermal boundary conductance (TBC) between the nanowire and the substrate it is fabricated on influences most of the performance metrics that make these detectors attractive for applications. This includes the maximum count rate, latency, jitter, and quantum efficiency. Despite its importance, the study of TBC in superconducting nanowire devices has not been done systematically, primarily due to the lack of a straightforward characterization method. Here, we show that simple electrical measurements can be used to estimate the TBC between nanowires and substrates and that these measurements match acoustic mismatch theory across a variety of substrates. Numerical simulations allow us to refine our understanding, however, open questions remain. This work should enable thermal engineering in superconducting nanowire electronics and cryogenic detectors for improved device performance.

cond-mat.supr-con↗

arXiv2021

Initial Design of a W-band Superconducting Kinetic Inductance Qubit (Kineticon)

Superconducting qubits are widely used in quantum computing research and industry. We describe a superconducting kinetic inductance qubit (and introduce the term Kineticon to describe it) operating at W-band frequencies with a nonlinear nanowire section that provides the anharmonicity required for two distinct quantum energy states. Operating the qubits at higher frequencies may relax the dilution refrigerator temperature requirements for these devices and paves the path for multiplexing a large number of qubits. Millimeter-wave operation requires superconductors with relatively high $T_c$, which implies high gap frequency, 2$Δ/h$, beyond which photons break Cooper pairs. For example, NbTiN with $T_c =15\,\text{K}$ has a gap frequency near 1.4 THz, which is much higher than that of aluminum (90 GHz), allowing for operation throughout the millimeter-wave band. Here we describe a design and simulation of a W-band Kineticon qubit embedded in a 3-D cavity. We perform classical electromagnetic calculations of the resulting field distributions.

quant-ph↗

arXiv2021

Development of an Array of Kinetic Inductance Magnetometers (KIMs)

We describe optimization of a cryogenic magnetometer that uses nonlinear kinetic inductance in superconducting nanowires as the sensitive element instead of a superconducting quantum interference device (SQUID). The circuit design consists of a loop geometry with two nanowires in parallel, serving as the inductive section of a lumped LC resonator similar to a kinetic inductance detector (KID). This device takes advantage of the multiplexing capability of the KID, allowing for a natural frequency multiplexed readout. The Kinetic Inductance Magnetometer (KIM) is biased with a DC magnetic flux through the inductive loop. A perturbing signal will cause a flux change through the loop, and thus a change in the induced current, which alters the kinetic inductance of the nanowires, causing the resonant frequency of the KIM to shift. This technology has applications in astrophysics, material science, and the medical field for readout of Metallic Magnetic Calorimeters (MMCs), axion detection, and magnetoencephalography (MEG).

physics.ins-det↗

arXiv2020

A compact and tunable forward coupler based on high-impedance superconducting nanowires

Developing compact, low-dissipation, cryogenic-compatible microwave electronics is essential for scaling up low-temperature quantum computing systems. In this paper, we demonstrate an ultra-compact microwave directional forward coupler based on high-impedance slow-wave superconducting-nanowire transmission lines. The coupling section of the fabricated device has a footprint of $416\,\mathrm{μm^2}$. At 4.753 GHz, the input signal couples equally to the through port and forward-coupling port (50:50) at $-6.7\,\mathrm{dB}$ with $-13.5\,\mathrm{dB}$ isolation. The coupling ratio can be controlled with DC bias current or temperature by exploiting the dependence of the kinetic inductance on these quantities. The material and fabrication-process are suitable for direct integration with superconducting circuits, providing a practical solution to the signal distribution bottlenecks in developing large-scale quantum computers.

physics.app-ph↗

arXiv2020

Superconducting MoN thin films prepared by DC reactive magnetron sputtering for nanowire single-photon detectors

We present a comprehensive study of molybdenum nitride (MoN) thin film deposition using direct current (DC) reactive magnetron sputtering. We have investigated the effect of various deposition conditions on the superconducting and electrical properties of the films. Furthermore, we have shown that meander-shaped single-photon detectors made from 5 nm MoN films have saturated quantum detection efficiency at the telecom wavelength of 1550 nm. Our results indicate that MoN may be a material of interest for practical applications of low-temperature superconductors, including single-photon detectors and transition-edge sensors.

cond-mat.supr-con↗

arXiv2020

Enhancing the Performance of Superconducting Nanowire-Based Detectors with High-Filling Factor by Using Variable Thickness

Current crowding at bends of superconducting nanowire single-photon detectors is one of the main factors limiting the performance of meander-style detectors with large filling factors. In this paper, we propose a new concept to reduce influence of the current crowding effect, a so-called variable thickness SNSPD, which is composed of two regions with different thicknesses. A larger thickness of bends in comparison to the thickness of straight nanowire sections locally reduces the current density and reduces the suppression of the critical current caused by the current crowding. This allows variable thickness SNSPD to have a higher critical current, an improved detection efficiency, and decreased dark count rate in comparison with a standard uniform thickness SNSPD with an identical geometry and film quality.

cond-mat.supr-con↗

arXiv2020

A superconducting nanowire spiking element for neural networks

As the limits of traditional von Neumann computing come into view, the brain's ability to communicate vast quantities of information using low-power spikes has become an increasing source of inspiration for alternative architectures. Key to the success of these largescale neural networks is a power-efficient spiking element that is scalable and easily interfaced with traditional control electronics. In this work, we present a spiking element fabricated from superconducting nanowires that has pulse energies on the order of ~10 aJ. We demonstrate that the device reproduces essential characteristics of biological neurons, such as a refractory period and a firing threshold. Through simulations using experimentally measured device parameters, we show how nanowire-based networks may be used for inference in image recognition, and that the probabilistic nature of nanowire switching may be exploited for modeling biological processes and for applications that rely on stochasticity.

q-bio.NC↗

arXiv2020

Large-area microwire MoSi single-photon detectors at 1550 nm wavelength

We demonstrate saturated internal detection efficiency at 1550 nm wavelengths for meander-shaped superconducting nanowire single-photon detectors made of 3 nm thick MoSi films with widths of 1 and 3 $μm$, and active areas up to 400 by 400 $μm^2$. Despite hairpin turns and a large number of squares (up to $10^4$) in the device, the dark count rate was measured to be ~10$^3$ cps at 99% of the switching current. This value is about two orders of magnitude lower than results reported recently for short MoSi devices with shunt resistors. We also found that 5 nm thick MoSi detectors with the same geometry were insensitive to single near-infrared photons, which may be associated with different levels of suppression of the superconducting order parameter. However, our results obtained on 3 nm thick MoSi devices are in a good agreement with predictions in the frame of a kinetic-equation approach.

physics.app-ph↗

arXiv2020

Cavity electro-optics in thin-film lithium niobate for efficient microwave-to-optical transduction

Linking superconducting quantum devices to optical fibers via microwave-optical quantum transducers may enable large scale quantum networks. For this application, transducers based on the Pockels electro-optic (EO) effect are promising for their direct conversion mechanism, high bandwidth, and potential for low-noise operation. However, previously demonstrated EO transducers require large optical pump power to overcome weak EO coupling and reach high efficiency. Here, we create an EO transducer in thin-film lithium niobate, leveraging the low optical loss and strong EO coupling in this platform. We demonstrate a transduction efficiency of up to $2.7\times10^{-5}$, and a pump-power normalized efficiency of $1.9\times10^{-6}/\mathrm{μW}$. The transduction efficiency can be improved by further reducing the microwave resonator's piezoelectric coupling to acoustic modes, increasing the optical resonator quality factor to previously demonstrated levels, and changing the electrode geometry for enhanced EO coupling. We expect that with further development, EO transducers in thin-film lithium niobate can achieve near-unity efficiency with low optical pump power.

quant-ph↗

arXiv2019

Resolving photon numbers using a superconducting tapered nanowire detector

Time- and number-resolved photon detection is crucial for photonic quantum information processing. Existing photon-number-resolving (PNR) detectors usually have limited timing and dark-count performance or require complex fabrication and operation. Here we demonstrate a PNR detector at telecommunication wavelengths based on a single superconducting nanowire with an integrated impedance-matching taper. The prototyping device was able to resolve up to five absorbed photons and had 16.1 ps timing jitter, <2 c.p.s. device dark count rate, $\sim$86 ns reset time, and 5.6% system detection efficiency (without cavity) at 1550 nm. Its exceptional distinction between single- and two-photon responses is ideal for coincidence counting and allowed us to directly observe bunching of photon pairs from a single output port of a Hong-Ou-Mandel interferometer. This detector architecture may provide a practical solution to applications that require high timing resolution and few-photon discrimination.

physics.ins-det↗

arXiv2019

Cryogenic Memory Architecture Integrating Spin Hall Effect based Magnetic Memory and Superconductive Cryotron Devices

One of the most challenging obstacles to realizing exascale computing is minimizing the energy consumption of L2 cache, main memory, and interconnects to that memory. For promising cryogenic computing schemes utilizing Josephson junction superconducting logic, this obstacle is exacerbated by the cryogenic system requirements that expose the technology's lack of high-density, high-speed and power-efficient memory. Here we demonstrate an array of cryogenic memory cells consisting of a non-volatile three-terminal magnetic tunnel junction element driven by the spin Hall effect, combined with a superconducting heater-cryotron bit-select element. The write energy of these memory elements is roughly 8 pJ with a bit-select element, designed to achieve a minimum overhead power consumption of about 30%. Individual magnetic memory cells measured at 4 K show reliable switching with write error rates below $10^{-6}$, and a 4x4 array can be fully addressed with bit select error rates of $10^{-6}$. This demonstration is a first step towards a full cryogenic memory architecture targeting energy and performance specifications appropriate for applications in superconducting high performance and quantum computing control systems, which require significant memory resources operating at 4 K.

physics.app-ph↗

arXiv2019

Measuring thickness in thin NbN films for superconducting devices

We present the use of a commercially available fixed-angle multi-wavelength ellipsometer for quickly measuring the thickness of NbN thin films for the fabrication and performance improvement of superconducting nanowire single photon detectors. The process can determine the optical constants of absorbing thin films, removing the need for inaccurate approximations. The tool can be used to observe oxidation growth and allows thickness measurements to be integrated into the characterization of various fabrication processes.

physics.app-ph↗