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Junction-free microwave two-mode radiation from a kinetic inductance nanowire
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In situ amplification of spin echoes within a kinetic inductance parametric amplifier
The use of superconducting microresonators together with quantum-limited Josephson parametric amplifiers has enhanced the sensitivity of pulsed electron spin resonance (ESR) measurements by more than four orders of magnitude. So far, the microwave resonators and amplifiers have been designed as separate components due to the incompatibility of Josephson junction–based devices with magnetic fields. This has produced complex spectrometers and raised technical barriers toward adoption of the technique. Here, we circumvent this issue by coupling an ensemble of spins directly to a weakly nonlinear and magnetic field–resilient superconducting microwave resonator. We perform pulsed ESR measurements with a 1-pL mode volume containing 6 × 10 7 spins and amplify the resulting signals within the device. When considering only those spins that contribute to the detected signals, we find a sensitivity of 2.8 x 10 3 spins / $\sqrt{Hz}$ for a Hahn echo sequence at a temperature of 400 mK. In situ amplification is demonstrated at fields up to 254 mT, highlighting the technique’s potential for application under conventional ESR operating conditions.
Direct Dark Matter Search with Kinetic Inductance Detectors [Poster]
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Kinetic Inductance Phonon-Mediated Detectors for Dark Matter: R&D at NEXUS
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Pyruvate, phosphate dikinase regulatory protein impacts light response of C4 photosynthesis in Setaria viridis
In C4 plants, the pyruvate (Pyr), phosphate dikinase regulatory protein (PDRP) regulates the activity of the C4 pathway enzyme Pyr, phosphate dikinase (PPDK) in a light-/dark-dependent manner. The importance of this regulatory action to C4 pathway function and overall C4 photosynthesis is unknown. To resolve this question, we assessed in vivo PPDK phospho-regulation and whole leaf photophysiology in a CRISPR–Cas9 PDRP knockout (KO) mutant of the NADP-ME C4 grass green millet (Setaria viridis). PDRP enzyme activity was undetectable in leaf extracts from PDRP KO lines. Likewise, PPDK phosphorylated at the PDRP-regulatory Thr residue was immunologically undetectable in leaf extracts. PPDK enzyme activity in rapid leaf extracts was constitutively high in the PDRP KO lines, irrespective of light or dark pretreatment of leaves. Gas exchange analysis of net CO2 assimilation revealed PDRP KO leaves had markedly slower light induction kinetics when leaves transition from dark to high-light or low-light to high-light. In the initial 30 min of the light induction phase, KO leaves had an ~15% lower net CO2 assimilation rate versus the wild-type (WT). Despite the impaired slower induction kinetics, we found growth and vigor of the KO lines to be visibly indistinguishable from the WT when grown in normal air and under standard growth chamber conditions. However, the PDRP KO plants grown under a fluctuating light regime exhibited a gradual multi-day decline in Fv/Fm, indicative of progressive photosystem II damage due to the absence of PDRP. Collectively, our results demonstrate that one of PDRP’s functions in C4 photosynthesis is to ensure optimal photosynthetic light induction kinetics during dynamic changes in incident light.
SCExAO/MEC and CHARIS Discovery of a Low-mass, 6 au Separation Companion to HIP 109427 Using Stochastic Speckle Discrimination and High-contrast Spectroscopy
We report the direct imaging discovery of a low-mass companion to the nearby accelerating A star, HIP 109427, with the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument coupled with the Microwave Kinetic Inductance Detector Exoplanet Camera (MEC) and CHARIS integral field spectrograph. CHARIS data reduced with reference star point spread function (PSF) subtraction yield 1.1–2.4 μm spectra. MEC reveals the companion in Y and J band at a comparable signal-to-noise ratio using stochastic speckle discrimination, with no PSF subtraction techniques. Combined with complementary follow-up L {sub p} photometry from Keck/NIRC2, the SCExAO data favors a spectral type, effective temperature, and luminosity of M4–M5.5, 3000–3200 K, and log{sub 10}(L/L{sub ⊙})=−2.28{sub −0.04}{sup +0.04}, respectively. Relative astrometry of HIP 109427 B from SCExAO/CHARIS and Keck/NIRC2, and complementary Gaia–Hipparcos absolute astrometry of the primary favor a semimajor axis of 6.55{sup +3.0} {sub −0.48} au, an eccentricity of 0.54{sub −0.15}{sup +0.28}, an inclination of 66.7{sub −14}{sup +8.5} degrees, and a dynamical mass of 0.280{sub −0.059}{sup +0.18} M {sub ⊙}. This work shows the potential for extreme AO systems to utilize speckle statistics in addition to widely used postprocessing methods to directly image faint companions to nearby stars near the telescope diffraction limit.
Interplay between phonon downconversion efficiency, density of states at Fermi energy, and intrinsic energy resolution for microwave kinectic inductance detectors
Microwave Kinetic Inductance detectors (MKIDs) have been recognized as a powerful new tool for single photon detection. These highly multiplexed superconducting devices give timing and energy measurement for every detected photon. However, the full potential of MKID single photon spectroscopy has not been reached , the achieved energy resolution is lower than expected from first principles. Here, we study the efficiency in the phonon downconversion process following the absorption of energetic photons in MKIDs. Assuming previously published material properties, we measure an average downconversion efficiency for three TiN resonators is $\eta$=0.14. We discuss how this efficiency can impact the intrinsic energy resolution of MKID, and how any uncertainty in the unknown density of electron states at the Fermi energy directly affects the efficiency estimations.
Simulating the Phonon Collection Efficiency in KIPMDs
Kinetic inductance phonon-mediated (KIPM) detectors use microwave kinetic inductance detectors (MKIDs) to read out phonon signals in the substrate. They are a promising class of detectors to be used in light dark matter (DM) searches due to their potential eV-scale sensitivity and native frequency-domain multiplexability. In order to improve upon the design of these detectors, simulations are needed to understand the effects of detector design on measurable physical parameters including the phonon collection efficiency, $\eta_{ph}$, which is defined as the ratio of phonon energy detected by the sensitive target element to the incident energy deposited in the substrate. This work simulates the phonon collection efficiency for a KIPMD currently operated at the Northwestern EXperimental Underground Site (NEXUS).
The KIPM Detector Consortium
Kinetic Inductance Phonon-Mediated (KIPM) Detectors, microcalorimeters that leverage kinetic inductance detectors (KIDs) to read out phonon signals from the device substrate, are an attractive architecture for low-threshold rare-event searches due to their large response to small changes in quasiparticle density and native multiplexability, enabling scalability. We have established a consortium comprising university and national lab groups dedicated to advancing the state-of-the-art in these detectors, with the ultimate goal of designing a detector with a kg-scale target mass and sub-eV threshold on energy deposited in the substrate, enabling searches for both light dark matter and low-energy neutrino interactions. This consortium brings together experts in KID design, phonon and quasiparticle dynamics, and noise modeling, along with specialized fabrication facilities, test platforms, and unique calibration capabilities. Recently, our consortium has demonstrated a sensor resolution (i.e., resolution in the quasiparticle channel) of 2.1 eV, the current record for such devices. The current focus of the consortium is modeling and improving the phonon collection efficiency and implementing low-Tc superconductors, both of which serve to improve the overall energy resolution and threshold of the detectors. In this talk, I will provide an overview of the consortium and its capabilities, highlight some recent results from its member groups, and discuss near term plans toward reaching the ultimate goal.
Wafer-Scale MgB 2 Superconducting Devices
Progress in superconducting device and detector technologies over the past decade has realized practical applications in quantum computers, detectors for far-infrared telescopes, and optical communications. Superconducting thin-film materials, however, have remained largely unchanged, with aluminum still being the material of choice for superconducting qubits and niobium compounds for high-frequency/high kinetic inductance devices. Magnesium diboride (MgB 2 ), known for its highest transition temperature (T c = 39 K) among metallic superconductors, is a viable material for elevated temperature and higher frequency superconducting devices moving toward THz frequencies. However, difficulty in synthesizing wafer-scale thin films has prevented implementation of MgB 2 devices into the application base of superconducting electronics. Here, we report ultrasmooth (<0.5 nm root-mean-square roughness) and uniform MgB 2 thin (<100 nm) films over 100 mm in diameter and present prototype devices fabricated with these films demonstrating key superconducting properties including an internal quality factor over 10 4 at 4.5 K and high tunable kinetic inductance in the order of tens of pH/sq in a 40 nm thick film. This advancement will enable development of elevated temperature, high-frequency superconducting quantum circuits, and devices.
Development Status of the KIPM Detector Consortium
A kinetic inductance phonon-mediated detector is a calorimeter that uses kinetic inductance detectors (KIDs) to read out phonon signals from the device substrate. We have established a consortium comprising university and national lab groups dedicated to advancing the state of the art in these detectors, with the ultimate goal of designing a detector with sub-eV threshold on energy deposited in the substrate, enabling searches for both light dark matter and low-energy neutrino interactions. This consortium brings together experts in KID design, phonon and quasi-particle dynamics, and noise modeling, along with specialized fabrication facilities, test platforms, and unique calibration capabilities. Recently, our consortium has demonstrated a resolution on energy absorbed by the sensor of 2.1 eV, the current record for phonon-sensitive KIDs. However, due to ∼ 1% phonon collection efficiency, the overall detector resolution was limited to 320 eV. Finally, the current focus of the consortium is modeling and improving the phonon collection efficiency and implementing low-T c superconductors, both of which serve to improve the overall energy resolution and threshold of the detectors.
Novel frequency tunable systems for superconducting cavities (Abbreviated Report)
Ultra-low loss microwave resonant cavities are the backbone of quantum information science (QIS) and axion/dark matter detection (ADMX), but one of the challenges in developing 3D cavity systems has been finding a tuning mechanism that does not drastically reduce the cavity quality factor (Q) but still provides a large operating bandwidth. To alleviate this limitation, we proposed to fabricate a high-Q, 3D microwave cavity with an integrated hybrid mechanical/electrical tuning scheme to achieve both coarse and rapid fine tuning. We implemented two tuning schemes: one using a shift in kinetic inductance and one utilizing mechanical motion. We found that the kinetic inductance method did not yield any tunability in the cavity mode, but the mechanical adjustment successfully moved the cavity resonance. The quality factors obtained were lower than originally proposed, but there is potential to improve the design on further iterations.
Noise Optimization for MKIDs with Different Design Geometries and Material Selections
The separation and optimization of noise components is critical to microwave-kinetic inductance detector (MKID) development. We analyze the effect of several changes to the lumped-element inductor and interdigitated capacitor geometry on the noise performance of a series of MKIDs intended for millimeter-wavelength experiments. We extract the contributions from two-level system noise in the dielectric layer, the generation-recombination noise intrinsic to the superconducting thin-film, and system white noise from each detector noise power spectrum and characterize how these noise components depend on detector geometry, material, and measurement conditions such as driving power and temperature. We observe a reduction in the amplitude of two-level system noise with both an elevated sample temperature and an increased gap between the fingers within the interdigitated capacitors for both aluminum and niobium detectors. We also verify the expected reduction of the generation-recombination noise and associated quasiparticle lifetime with reduced inductor volume. This study also iterates over different materials, including aluminum, niobium, and aluminum manganese, and compares the results with an underlying physical model.
Sketched Nanoscale KTaO 3 -Based Superconducting Quantum Interference Device
The discovery of two-dimensional superconductivity in LaAlO 3 /KTaO 3 (111) and (110) interfaces has raised significant interest in this system. In this paper, we report the first successful fabrication of a direct current superconducting quantum interference device (dc-SQUID) in the KTO system. The key device elements, superconducting weak links, are created by conductive atomic force microscope lithography, which can reversibly control the conductivity at the LAO/KTO (110) interface with nanoscale resolution. The periodic modulation of the SQUID critical current 𝐼 c (𝐵) with magnetic field corresponds well with our theoretical modeling, which reveals a large kinetic inductance of the superconducting two-dimensional electron gas in KTO. The kinetic inductance of the SQUID is tunable by electrical gating from the back, due to the large dielectric constant of KTO. The demonstration of weak links and SQUIDs in KTO broadens the scope for exploring the underlying physics of KTO superconductivity, including the role of spin-orbit coupling, pairing symmetry, and inhomogeneity. It also promotes KTO as a versatile platform for a growing family of quantum devices, which could be applicable in the realm of quantum computing and information.
Simulating the Phonon Collection Efficiency in KIPMDs
Kinetic inductance phonon-mediated (KIPM) detectors are superconducting microcalorimeters that use microwave kinetic inductance detectors (MKIDs) to read out phonon signals in the device substrate. In order to improve the design of these detectors, we need to understand the effect of various detector design elements on the physical processes that take place within the detector through simulation efforts. One figure of merit for KIPM detectors is the phonon collection efficiency, $\eta_{ph]$, defined as the ratio of phonon energy detected by the sensitive element in the detector and the energy deposited by incident phonons in the substrate. Comparing the phonon collection efficiency obtained in simulation and in experiment for the same detector geometry provides insight to physical processes in the detector, such as phonon absorption at substrate-sensor interfaces and phonon loss to non-sensitive detector elements. This work models the phonon collection efficiency in two KIPM detectors with different geometries, one located at the Fermi National Accelerator Laboraory, the other located at the SLAC National Accelerator Laboratory.
Large microwave inductance of granular boron-doped diamond superconducting films
Boron-doped diamond granular thin films are known to exhibit superconductivity with an optimal critical temperature of T c =7.2 K. Here, we report the measured in-plane complex surface impedance of boron-doped diamond films in the microwave frequency range using a resonant technique. Experimentally measured inductance values are in good agreement with estimates obtained from the normal state sheet resistance of the material. Additionally, the magnetic penetration depth temperature dependence is consistent with that of a fully gapped s-wave superconductor. Boron-doped diamond films should find application where high kinetic inductance is needed, such as microwave kinetic inductance detectors and quantum impedance devices.
Characterization of MKIDs for CMB Observation at 220 GHz With the South Pole Telescope
We present an updated design of the 220 GHz microwave kinetic inductance detector (MKID) pixel for SPT-3G+, the next-generation camera for the South Pole Telescope. We show results of the dark testing of a 63-pixel array with mean inductor quality factor $Q_{i} = 4.8 \times 10^{5}$, aluminum inductor transition temperature $T_{c} = 1.19$K, and kinetic inductance fraction $\alpha _{k} = 0.32$. We optically characterize both the microstrip-coupled and CPW-coupled resonators, and find both have a spectral response close to prediction with an optical efficiency of $\eta \sim 70\%$. However, we find slightly lower optical response on the lower edge of the band than predicted, with neighboring dark detectors showing more response in this region, though at level consistent with less than 5% frequency shift relative to the optical detectors. The detectors show polarized response consistent with expectations, with a cross-polar response of $\sim 10\%$for both detector orientations.