arXiv subjects

K. K. Berggren

Publications and source records attributed to K. K. Berggren.

At least 19 recordsLinked to original sources

arXiv2023

Single-photon detection using large-scale high-temperature MgB$_2$ sensors at 20 K

Ultra-fast single-photon detectors with high current density and operating temperature can benefit space and ground applications, including quantum optical communication systems, lightweight cryogenics for space crafts, and medical use. Here we demonstrate magnesium diboride (MgB$_2$) thin-film superconducting microwires capable of single-photon detection at 1.55 $μ$m optical wavelength. We used helium ions to alter the properties of MgB$_2$, resulting in microwire-based detectors exhibiting single-photon sensitivity across a broad temperature range of up to 20 K, and detection efficiency saturation for 1 $μ$m wide microwires at 3.7 K. Linearity of detection rate vs incident power was preserved up to at least ~100 Mcps. Despite the large active area of up to 400$\times$400 $μ$m$^2$, the reset time was found to be as low as $\sim1$ ns. Our research provides new possibilities for breaking the operating temperature limit and maximum single-pixel count rate, expanding the detector area, and raises inquiries about the fundamental mechanisms of single-photon detection in high-critical-temperature superconductors.

cond-mat.supr-con↗

arXiv2023

Axion Dark Matter

Axions are well-motivated dark matter candidates with simple cosmological production mechanisms. They were originally introduced to solve the strong CP problem, but also arise in a wide range of extensions to the Standard Model. This Snowmass white paper summarizes axion phenomenology and outlines next-generation laboratory experiments proposed to detect axion dark matter. There are vibrant synergies with astrophysical searches and advances in instrumentation including quantum-enabled readout, high-Q resonators and cavities and large high-field magnets. This white paper outlines a clear roadmap to discovery, and shows that the US is well-positioned to be at the forefront of the search for axion dark matter in the coming decade.

hep-ex↗

arXiv2022

Single-photon detection using high-temperature superconductors

The detection of individual quanta of light is important for quantum computation, fluorescence lifetime imaging, single-molecule detection, remote sensing, correlation spectroscopy, and more. Thanks to their broadband operation, high detection efficiency, exceptional signal-to-noise ratio, and fast recovery times, superconducting nanowire single-photon detectors (SNSPDs) have become a critical component in these applications. The operation of SNSPDs based on conventional superconductors, which have a low critical temperature ($T_c$), requires costly and bulky cryocoolers. This motivated exploration of other superconducting materials with higher $T_c$ that would enable single-photon detection at elevated temperatures, yet this task has proven exceedingly difficult. Here we show that with proper processing, high-$T_c$ cuprate superconductors can meet this challenge. We fabricated superconducting nanowires (SNWs) out of thin flakes of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ and La$_{1.55}$Sr$_{0.45}$CuO$_4$/La$_2$CuO$_4$ (LSCO-LCO) bilayer films and demonstrated their single-photon response up to $25$ and $8$ K, respectively. The single-photon operation is revealed through the linear scaling of the photon count rate (PCR) on the radiation power. Both of our cuprate-based SNSPDs exhibited single-photon sensitivity at the technologically-important $1.5$ $μ$m telecommunications wavelength. Our work expands the family of superconducting materials for SNSPD technology, opens the prospects of raising the temperature ceiling, and raises important questions about the underlying mechanisms of single-photon detection by unconventional superconductors.

cond-mat.supr-con↗

arXiv2020

Single-photon detection in the mid-infrared up to 10 micron wavelength using tungsten silicide superconducting nanowire detectors

We developed superconducting nanowire single-photon detectors (SNSPDs) based on tungsten silicide (WSi) that show saturated internal detection efficiency up to a wavelength of 10 um. These detectors are promising for applications in the mid-infrared requiring ultra-high gain stability, low dark counts, and high efficiency such as chemical sensing, LIDAR, dark matter searches and exoplanet spectroscopy.

physics.ins-det↗

arXiv2019

Demonstration of microwave multiplexed readout of DC biased superconducting nanowire detectors

Superconducting nanowires are widely used as sensitive single photon detectors with wide spectral coverage and high timing resolution. We describe a demonstration of an array of DC biased superconducting nanowire single photon detectors read out with a microwave multiplexing circuit. In this design, each individual nanowire is part of a resonant LC circuit where the inductance is dominated by the kinetic inductance of the nanowire. The circuit also contains two parallel plate capacitors, one of them is in parallel with the inductor and the other is coupled to a microwave transmission line which carries the signals to a cryogenic low noise amplifier. All of the nanowires are connected via resistors to a single DC bias line that enables the nanowires to be current biased close to their critical current. When a photon hits a nanowire it creates a normal hot spot which produces a voltage pulse across the LC circuit. This pulse rings down at the resonant frequency of the LC circuit over a time period that is fixed by the quality factor. We present measurements of an array of these devices and an evaluation of their performance in terms of frequency and time response.

physics.ins-det↗

arXiv2019

Determining the depairing current in superconducting nanowire single-photon detectors

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.

cond-mat.supr-con↗

arXiv2019

Jitter Characterization of a Dual-Readout SNSPD

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

physics.ins-det↗

arXiv2018

Antiresonance-Like Behavior in Carrier-Envelope-Phase-Sensitive Optical-Field Photoemission from Plasmonic Nanoantennas

Given the quasi-static nature of optical-field emission and the nontrivial dependence of the emission rate on the instantaneous electric field strength, the CEP-sensitive component of the emitted photocurrent is highly sensitive to the energy of the optical pulse, and should carry information about the underlying sub-cycle dynamics of electron emission. Here we examine CEP-sensitive photoemission from plasmonic gold nanoantennas excited with few-cycle optical pulses of increasing energy. We observe antiresonance-like features in the CEP-sensitive photocurrent; specifically, at a critical pulse energy, we observe a sharp dip in the magnitude of the CEP-sensitive photocurrent accompanied by a sudden shift of π-radians in the phase of the photocurrent. Using a quasi-static tunneling emission model, we find that these antiresonance-like features arise due to competition between electron emission from neighboring optical half-cycles, and that they are highly sensitive to the precise shape of the driving optical waveform at the surface of the emitter. As the underlying mechanisms that produce the antiresonance-like features are a general consequence of nonlinear, field-driven photoemission, the antiresonance-like features could be used to probe sub-optical-cycle, sub-femtosecond emission processes, not only from solid-state emitters, but also from gas-phase atoms and molecules. Beyond applications in the study of ultrafast, field-driven electron physics, an understanding of these antiresonance-like features will be critical to the development of novel photocathodes for future time-domain metrology and microscopy applications that demand both attosecond temporal and nanometer spatial resolution.

physics.optics↗

arXiv2018

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

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.

physics.ins-det↗

arXiv2012

Improvement of infrared single-photon detectors absorptance by integrated plasmonic structures

The absorptance of p-polarized light in superconducting-nanowire single-photon detectors (SNSPDs) was improved by integrating (1) ~quarter-wavelength nano-optical cavity closed by a gold reflector (OC-SNSPD), (2) nano-cavity-array closed by vertical and horizontal gold segments (NCAI-SNSPD), and (3) nano-cavity-deflector-array consisting of longer vertical gold segments (NCDAI-SNSPD) into short- (p-) and long- (3p-) periodic niobium-nitride (NbN) stripe-patterns. In OC-SNSPDs the highest absorptance is observable at perpendicular incidence onto NbN stripes in P-orientation due to E-field concentration at the bottom of nano- cavities. In short-periodic NCAI-SNSPDs off-axis illumination results in almost polar-angle-independent perfect absorptance due to collective resonances on plasmonic MIM nano-cavity-arrays in S-orientation. In long-periodic NCAI-SNSPDs the surface wave-excitation phenomena promote EM-field transportation to the NbN stripes in S-orientation and results in local absorptance maxima. In NCDAI-SNSPDs with proper periodicity large absorptance maxima appear due to synchronous E-field enhancement via deflected SPPs below NbN stripes in S-orientation, which make possible fill-factor-related loss compensation.

physics.optics↗

arXiv2012

Bubble Nucleation on Nano- to Micro-size Cavities and Posts: An Experimental Validation of Classical Theory

Recently-reported data suggest that bubble nucleation on surfaces with nano-sized features (cavities and posts) may occur close to the thermodynamic saturation temperature. However, according to the traditional theory of heterogeneous bubble nucleation, such low nucleation temperatures are possible only for surfaces with micro-scale cavities. Motivated by this apparent contradiction, we have used infrared thermometry to measure the nucleation temperature of water on custom-fabricated nano- to micro-scale cavities (from 90 nm to 4.5 um in diameter) and posts (from 60 nm to 5 um in diameter), machined on ultra-smooth and clean silicon wafers using electron beam lithography. Our cavity data are in agreement with the predictions of the Young-Laplace equation, thus re-affirming the correctness of the classic view of heterogeneous bubble nucleation, at least for the water-silicon system investigated here. The data also suggest that individual posts of any size have an insignificant effect on bubble nucleation, as expected from theory. Keywords: Bubble nucleation, superheat, artificial cavities and posts, nanosize, Young-Laplace

physics.flu-dyn↗

arXiv2012

Critical-Current Reduction in Thin Superconducting Wires Due to Current Crowding

We demonstrate experimentally that the critical current in superconducting NbTiN wires is dependent on their geometrical shape, due to current-crowding effects. Geometric patterns such as 90 degree corners and sudden expansions of wire width are shown to result in the reduction of critical currents. The results are relevant for single-photon detectors as well as parametric amplifiers.

cond-mat.supr-con↗

arXiv2012

Timing performance of 30-nm-wide superconducting nanowire avalanche photodetectors

We investigated the timing jitter of superconducting nanowire avalanche photodetectors (SNAPs, also referred to as cascade switching superconducting single photon detectors) based on 30-nm-wide nanowires. At bias currents (IB) near the switching current, SNAPs showed sub 35 ps FWHM Gaussian jitter similar to standard 100 nm wide superconducting nanowire single-photon detectors. At lower values of IB, the instrument response function (IRF) of the detectors became wider, more asymmetric, and shifted to longer time delays. We could reproduce the experimentally observed IRF time-shift in simulations based on an electrothermal model, and explain the effect with a simple physical picture.

physics.ins-det↗

arXiv2012

Afterpulsing and Instability in Superconducting Nanowire Avalanche Photodetectors

We investigated the reset time of superconducting nanowire avalanche photodetectors (SNAPs) based on 30 nm wide nanowires. We studied the dependence of the reset time of SNAPs on the device inductance and discovered that SNAPs can provide a speed-up relative to SNSPDs with the same area, but with some limitations: (1) reducing the series inductance of SNAPs (necessary for the avalanche formation) could result in the detectors operating in an unstable regime; (2) a trade-off exists between maximizing the bias current margin and minimizing the reset time of SNAPs; and (3) reducing the reset time of SNAPs below ~ 1 ns resulted in afterpulsing.

physics.ins-det↗

arXiv2011

Single-photon detectors based on ultra-narrow superconducting nanowires

Superconducting nanowire single-photon detectors (SNSPDs) perform single-photon counting with exceptional sensitivity and time resolution at near-infrared wavelengths. State-of-the-art SNSPDs, based on 100 nm-wide, 4 to 5 nm thick NbN nanowires, are vulnerable to constrictions, which significantly limit their yield. Also, their sensitivity becomes negligible beyond 2 μm wavelength, which makes them unsuitable for mid-infrared applications. SNSPDs based on few-tens-of-nanometer-wide nanowires are expected to efficiently detect mid-infrared photons and to operate at low bias currents, so constrictions may have less impact on their performance. Prior to this work, SNSPDs based on nanowires narrower than 50-nm had not been demonstrated because: (1) the SNSPD signal is roughly proportional to the nanowire width, so narrow nanowires have poor signal-to-noise ratio; and (2) fabrication at these length scales is extremely challenging. In this letter we report how we addressed these issues and demonstrated single-photon detection (20% detection efficiency at 1550 nm wavelength) with 30- and 20-nm-wide-nanowire detectors.

quant-ph↗

arXiv2007

Microwave-Induced Cooling of a Superconducting Qubit

We demonstrated microwave-induced cooling in a superconducting flux qubit. The thermal population in the first-excited state of the qubit is driven to a higher-excited state by way of a sideband transition. Subsequent relaxation into the ground state results in cooling. Effective temperatures as low as Teff~ 3 millikelvin are achieved for bath temperatures Tbath = 30 - 400 millikelvin, a cooling factor between 10 and 100. This demonstration provides an analog to optical cooling of trapped ions and atoms and is generalizable to other solid-state quantum systems. Active cooling of qubits, applied to quantum information science, provides a means for qubit-state preparation with improved fidelity and for suppressing decoherence in multi-qubit systems.

cond-mat.supr-con↗

arXiv2006

Coherent Quasiclassical Dynamics of a Persistent Current Qubit

A new regime of coherent quantum dynamics of a qubit is realized at low driving frequencies in the strong driving limit. Coherent transitions between qubit states occur via the Landau-Zener process when the system is swept through an energy-level avoided crossing. The quantum interference mediated by repeated transitions gives rise to an oscillatory dependence of the qubit population on the driving field amplitude and flux detuning. These interference fringes, which at high frequencies consist of individual multiphoton resonances, persist even for driving frequencies smaller than the decoherence rate, where individual resonances are no longer distinguishable. A theoretical model that incorporates dephasing agrees well with the observations.

cond-mat.supr-con↗

arXiv2005

Multi-Photon, Multi-Level Dynamics in a Superconducting Persistent-Current Qubit

Single-, two-, and three-photon transitions were driven amongst five quantum states of a niobium persistent-current qubit. A multi-level energy-band diagram was extracted using microwave spectroscopy, and avoided crossings were directly measured between the third and fourth excited states. The energy relaxation times between states connected by single-photon and multi-photon transitions were approximately 30 - 100 microseconds. Three-photon coherent oscillations were observed between the qubit ground and fourth excited states with a decoherence time of approximately 50 nanoseconds.

cond-mat.supr-con↗