arXiv subjects

Arjan F. van Loo

Publications and source records attributed to Arjan F. van Loo.

At least 19 recordsLinked to original sources

arXiv2026

Extended High-Mass Axion Search with an Auxetically Tuned Higher-Order-Mode Cavity

Conventional high-mass axion haloscopes based on the TM$_{010}$ mode lose detection volume as the resonant frequency increases. We report an extended axion search using a dielectric-restored TM$_{020}$ cavity haloscope with symmetry-preserving auxetic tuning based on a single-degree-of-freedom mechanical architecture. Using a near-quantum-limited microwave receiver, we searched a frequency range of 4.98-5.07 GHz and exclude axion-photon couplings with sensitivity approaching the KSVZ benchmark. Together with two earlier searches, the present scans extend a multi-scan program based on this architecture, yielding nearly 300 MHz of contiguous high-mass axion coverage over 4.98-5.27 GHz, the first broad search reported with a single higher-order-mode haloscope. This work establishes higher-order-mode cavities as a practical, scalable route beyond the TM$_{010}$ volume penalty.

hep-ex↗

arXiv2026

Extended Haloscope Search and Exclusion of a Candidate Signal near 1.036 GHz

We report a follow-up axion haloscope search near 1.036 GHz that completes and extends our previous work [Phys. Rev. X 14, 031023 (2024)], in which a portion of the HEMT-based data could not be analyzed due to unrecorded experimental information. While recovering this dataset, we identified an excess near 1.036 GHz that satisfied our candidate-selection criteria, motivating dedicated validation studies, including independent cross-checks and re-examination with the original apparatus. The excess did not persist under these investigations and was not confirmed as an axion dark-matter signal. We subsequently extended the search over a 20-MHz band surrounding the candidate using a quantum-noise-limited amplifier, achieving sensitivity close to the Dine-Fischler-Srednicki-Zhitnitsky benchmark. In the absence of a confirmed signal, we set improved 90% confidence-level upper limits on the axion-photon coupling over the frequency range 1.026-1.045 GHz. This work highlights the importance of robust candidate-validation strategies as haloscope searches approach discovery-level sensitivity.

hep-ex↗

arXiv2026

High-gain and large-bandwidth Josephson parametric amplifier influenced by Fabry-Pérot interference

Quantum-limited parametric amplifiers are essential components for many quantum technologies operating in the microwave domain. Achieving both high gain and broad bandwidth, however, remains challenging due to trade-offs between gain and bandwidth, pump efficiency, and dynamic range. Moreover, high-gain broadband amplifiers become increasingly sensitive to their external electromagnetic environment, which can distort their gain spectra and hinder reliable operation. Here, we present an accurate theoretical model and a systematic design methodology for a flux-driven, lumped-element Josephson parametric amplifier based on a SQUID array. Our device achieves near-quantum-limited, phase-preserving amplification with a net gain of 20 (maximally 44) dB and a 3-dB bandwidth of $\sim$50 ($\lesssim$0.2) MHz. We further show that the gain spectra exhibit pronounced sensitivity to weak reflections in the input-output waveguide caused by impedance mismatches in the microwave environment. By incorporating Fabry-Pérot-type interference into a quantum input-output model, we analytically reproduce these complex spectral features and identify how they depend on the physical parameters of the environment. More generally, our results provide a practical framework for separating the intrinsic dynamics of parametric amplifiers from environmental effects. This approach enables reliable characterization and optimization of amplifier performance while providing a systematic strategy for diagnosing microwave reflections and engineering environmental interference to shape amplifier gain spectra, thereby offering a pathway toward robust, reproducible, and truly quantum-limited microwave amplification.

quant-ph↗

arXiv2025

Search for high-frequency gravitational waves via re-analysis of cavity axion data

Monochromatic high-frequency gravitational waves (HFGW) provide a distinctive probe of new physics scenarios, most notably axion clouds around rotating black holes formed via superradiance. We reanalyzed data from the CAPP-12T MC (multi-cell) axion haloscope experiment [Phys. Rev. Lett. 133,051802 (2024)]. The study covers a continuous $2\,$MHz frequency span centered at $5.311\,$GHz. No rescan candidates were found, and we set 90% confidence-level exclusion limits on the gravitational-wave strain, reaching $h_0 \approx 3.9 \times 10^{-21}$ in the most sensitive regions of the sky. Interpreted in the context of black-hole superradiance from axion clouds, the results exclude black holes with mass $M_{\mathrm{BH}} \simeq 1.22 \times 10^{-6}\,M_\odot$ within distances of $O(10^{-2})\,$AU from Earth, under benchmark assumptions. This work demonstrates the potential of electromagnetic resonant cavities as novel detectors of monochromatic HFGW and motivates future searches for both long-lived and transient signals.

hep-ex↗

arXiv2025

Probing KSVZ Axion Dark Matter near 5.9 GHz Using a 8-Cell Cavity Haloscope

We report on a search for axion dark matter in the frequency range near 5.9 GHz, conducted using the haloscope technique. The experiment employed an 8-cell microwave resonator designed to extend the accessible frequency range by a multi-fold factor relative to conventional single-cell configurations, while maintaining a large detection volume. To enhance sensitivity, a flux-driven Josephson parametric amplifier (JPA) operating near the quantum noise limit was utilized, together with a sideband-summing method that coherently combines mirrored spectral components generated by the JPA. Data were acquired over the frequency range 5.83-5.94 GHz. With no statistically significant excess observed, we exclude axion-photon couplings $g_{aγγ}$ down to $1.2 \times 10^{-14}$ GeV$^{-1}$ at a 90% confidence level. The achieved sensitivity approaches the KSVZ benchmark prediction, setting the most stringent limits to date in this range.

hep-ex↗

arXiv2025

Axion Dark Matter Search with Near-KSVZ Sensitivity Using the TM$_{020}$ Mode

Dark matter remains one of the most profound mysteries in modern physics, with axions, a hypothetical particle proposed to resolve the strong CP problem, standing as a compelling candidate. Among various experimental strategies, cavity haloscopes currently offer the most sensitive method to detect axions, though their searches have largely been confined to axion masses below 10 $μ$eV. However, recent theoretical developments suggest that the axion mass lies beyond this range. Higher-order cavity modes have been explored as a methodological approach to expand the search range, albeit with limited success in achieving both high sensitivity and broad tunability. In this work, we present a sensitive search for axions with masses around 21 $μ$eV, utilizing the TM$_{020}$ mode of a cylindrical cavity, which incorporated an innovative tuning mechanism. Our results reached 1.7 times the KSVZ sensitivity over 100 MHz, representing a significant improvement in this mass range and contributing to the experimental search for axion dark matter at higher masses.

hep-ex↗

arXiv2024

Fast multiplexed superconducting qubit readout with intrinsic Purcell filtering

Fast and accurate qubit measurement remains a critical challenge on the path to fault-tolerant quantum computing. In superconducting quantum circuits, fast qubit measurement has been achieved using a dispersively coupled resonator with a large external linewidth. This necessitates the use of a Purcell filter that protects the qubit from relaxation through the readout channel. Here we show that a readout resonator and filter resonator, coupled to each other both capacitively and inductively, can produce a compact notch-filter circuit that effectively eliminates the Purcell decay channel through destructive interference. By utilizing linewidths as large as 42 MHz, we perform 56-ns simultaneous readout of four qubits and benchmark an average assignment fidelity of 99.77%, with the highest qubit assignment fidelity exceeding 99.9%. These results demonstrate a significant advancement in speed and fidelity for multiplexed superconducting qubit readout.

quant-ph↗

arXiv2024

Experimental search for invisible dark matter axions around 22 μeV

The axion has emerged as the most attractive solution to two fundamental questions in modern physics related to the charge-parity invariance in strong interactions and the invisible matter component of our universe. Over the past decade, there have been many theoretical efforts to constrain the axion mass based on various cosmological assumptions. Interestingly, different approaches from independent groups produce good overlap between 20 and 30 μeV. We performed an experimental search to probe the presence of dark matter axions within this particular mass region. The experiment utilized a multi-cell cavity haloscope embedded in a 12 T magnetic field to seek for microwave signals induced by the axion-photon coupling. The results ruled out the KSVZ axions as dark matter over a mass range between 21.86 and 22.00 μeV at a 90% confidence level. This represents a sensitive experimental search guided by specific theoretical predictions

hep-ex↗

arXiv2024

Josephson Parametric Amplifier based Quantum Noise Limited Amplifier Development for Axion Search Experiments in CAPP

This paper provides a comprehensive overview of the development of flux-driven Josephson Parametric Amplifiers (JPAs) as Quantum Noise Limited Amplifier for axion search experiments conducted at the Center for Axion and Precision Physics Research (CAPP) of the Institute for Basic Science. It focuses on the characterization, and optimization of JPAs, which are crucial for achieving the highest sensitivity in axion particle detection. We discuss various characterization techniques, methods for improving bandwidth, and the attainment of ultra-low noise temperatures. JPAs have emerged as indispensable tools in CAPPs axion search endeavors, playing a significant role in advancing our understanding of fundamental physics and unraveling the mysteries of the universe.

hep-ex↗

arXiv2024

Parameter optimization of Josephson parametric amplifiers using a heuristic search algorithm for axion haloscope search

The cavity haloscope is among the most widely adopted experimental platforms designed to detect dark matter axions with its principle relying on the conversion of axions into microwave photons in the presence of a strong magnetic field. The Josephson parametric amplifier (JPA), known for its quantum-limited noise characteristics, has been incorporated in the detection system to capture the weakly interacting axion signals. However, the performance of the JPA can be influenced by its environment, leading to potential unreliability of a predefined parameter set obtained in a specific laboratory setting. Furthermore, conducting a broadband search requires consecutive characterization of the amplifier across different tuning frequencies. To ensure more reliable measurements, we utilize the Nelder-Mead technique as a numerical search method to dynamically determine the optimal operating conditions. This heuristic search algorithm explores the multidimensional parameter space of the JPA, optimizing critical characteristics such as gain and noise temperature to maximize signal-to-noise ratios for a given experimental setup. Our study presents a comprehensive analysis of the properties of a flux-driven JPA to demonstrate the effectiveness of the algorithm. This approach contributes to ongoing efforts in axion dark matter research by offering an efficient method to enhance axion detection sensitivity through the optimized utilization of JPAs.

physics.ins-det↗

arXiv2024

Extensive search for axion dark matter over 1\,GHz with CAPP's Main Axion eXperiment

We report an extensive high-sensitivity search for axion dark matter above 1\,GHz at the Center for Axion and Precision Physics Research (CAPP). The cavity resonant search, exploiting the coupling between axions and photons, explored the frequency (mass) range of 1.025\,GHz (4.24\,$μ$eV) to 1.185\,GHz (4.91\,$μ$eV). We have introduced a number of innovations in this field, demonstrating the practical approach of optimizing all the relevant parameters of axion haloscopes, extending presently available technology. The CAPP 12\,T magnet with an aperture of 320\,mm made of Nb$_3$Sn and NbTi superconductors surrounding a 37-liter ultralight-weight copper cavity is expected to convert DFSZ axions into approximately $10^2$ microwave photons per second. A powerful dilution refrigerator, capable of keeping the core system below 40\,mK, combined with quantum-noise limited readout electronics, achieved a total system noise of about 200\,mK or below, which corresponds to a background of roughly $4\times 10^3$ photons per second within the axion bandwidth. The combination of all those improvements provides unprecedented search performance, imposing the most stringent exclusion limits on axion--photon coupling in this frequency range to date. These results also suggest an experimental capability suitable for highly-sensitive searches for axion dark matter above 1\,GHz.

hep-ex↗

arXiv2023

Search for the Sagittarius Tidal Stream of Axion Dark Matter around 4.55 $μ$eV

We report the first search for the Sagittarius tidal stream of axion dark matter around 4.55 $μ$eV using CAPP-12TB haloscope data acquired in March of 2022. Our result excluded the Sagittarius tidal stream of Dine-Fischler-Srednicki-Zhitnitskii and Kim-Shifman-Vainshtein-Zakharov axion dark matter densities of $ρ_a\gtrsim0.184$ and $\gtrsim0.025$ GeV/cm$^{3}$, respectively, over a mass range from 4.51 to 4.59 $μ$eV at a 90% confidence level.

hep-ex↗

arXiv2023

Four-channel System for Characterization of Josephson Parametric Amplifiers

The axion search experiments based on haloscopes at the Center for Axion and Precision Physics Research (CAPP) of the Institute for Basic Science (IBS) in South Korea are performed in the frequency range from 1 GHz to 6 GHz. In order to perform the experiments in a strong magnetic field of 12 T and a large-volume cavity of close to 40 liters, we use He wet dilution refrigerators with immersed superconducting magnets. The measurements require continuous operation for months without interruptions for microwave component replacements. This is achieved by using different cryogenic engineering approaches including microwave RF-switching. The critical components, defining the scanning rate and the sensitivity of the setup, are the Josephson parametric amplifiers (JPA) and cryogenic low noise amplifiers (cLNA) based on high-electron-mobility-transistor (HEMT) technology. It is desirable for both devices to have a wide frequency range and low noise close to the quantum limit for the JPA. In this paper, we show a recent design of a 4-channel measurement setup for JPA and HEMT measurements. The setup is based on a 4-channel wideband noise source (NS) and is used for both JPA and HEMT gain and noise measurements. The setup is placed at 20 mK inside the dry dilution refrigerator. The NS is thermally decoupled from the environment using plastic spacers, superconducting wires and superconducting coaxial cables. We show the gain and noise temperature curves measured for 4 HEMT amplifiers and 2 JPAs in one cool-down

cond-mat.supr-con↗

arXiv2023

Systematic Approach for Tuning Flux-driven Josephson Parametric Amplifiers for Stochastic Small Signals

Many experiments operating at millikelvin temperatures with signal frequencies in the microwave regime are beginning to incorporate Josephson Parametric Amplifiers (JPA) as their first amplification stage. While there are implementations for a wideband frequency response with a minimal need for tuning, designs using resonant structures with small numbers of Josephson elements still achieve the best noise performance. In a typical measurement scheme involving a JPA, one needs to control the resonance frequency, pump frequency and pump power to achieve the desired amplification and noise properties. In this work, we propose a straightforward approach for operating JPAs with the help of a look-up table (LUT) and online fine-tuning. Using the proposed approach, we demonstrate the operation of a flux-driven JPA with 20 dB gain around 5.9 GHz, covering approximately 100 MHz with 20 kHz tuning steps. The proposed methodology was successfully used in the context of a haloscope axion experiment.

physics.ins-det↗

arXiv2023

Axion Dark Matter Search around 4.55 $μ$eV with Dine-Fischler-Srednicki-Zhitnitskii Sensitivity

We report an axion dark matter search at Dine-Fischler-Srednicki-Zhitnitskii sensitivity with the CAPP-12TB haloscope, assuming axions contribute 100\% of the local dark matter density. The search excluded the axion--photon coupling $g_{aγγ}$ down to about $6.2\times10^{-16}$ GeV$^{-1}$ over the axion mass range between 4.51 and 4.59 $μ$eV at a 90\% confidence level. The achieved experimental sensitivity can also exclude Kim-Shifman-Vainshtein-Zakharov axion dark matter that makes up just 13\% of the local dark matter density. The CAPP-12TB haloscope will continue the search over a wide range of axion masses.

hep-ex↗

arXiv2021

Characterization of a flux-driven Josephson parametric amplifier with near quantum-limited added noise for axion search experiments

The axion, a hypothetical elementary pseudoscalar, is expected to solve the strong CP problem of QCD and is also a promising candidate for dark matter. The most sensitive axion search experiments operate at millikelvin temperatures and hence rely on instrumentation that carries signals from a system at cryogenic temperatures to room temperature instrumentation. One of the biggest limiting factors affecting the parameter scanning speed of these detectors is the noise added by the components in the signal detection chain. Since the first amplifier in the chain limits the minimum noise, low-noise amplification is of paramount importance. This paper reports on the operation of a flux-driven Josephson parametric amplifier (JPA) operating at around 2.3 GHz with added noise approaching the quantum limit. The JPA was employed as a first stage amplifier in an experimental setting similar to the ones used in haloscope axion detectors. By operating the JPA at a gain of 19 dB and cascading it with two cryogenic amplifiers operating at 4 K, noise temperatures as low as 120 mK were achieved for the whole signal detection chain.

cond-mat.supr-con↗

arXiv2019

Microwave magnon damping in YIG films at millikelvin temperatures

Magnon systems used in quantum devices require low damping if coherence is to be maintained. The ferrimagnetic electrical insulator yttrium iron garnet (YIG) has low magnon damping at room temperature and is a strong candidate to host microwave magnon excitations in future quantum devices. Monocrystalline YIG films are typically grown on gadolinium gallium garnet (GGG) substrates. In this work, comparative experiments made on YIG waveguides with and without GGG substrates indicate that the material plays a significant role in increasing the damping at low temperatures. Measurements reveal that damping due to temperature-peak processes is dominant above 1 K. Damping behaviour that we show can be attributed to coupling to two-level fluctuators (TLFs) is observed below 1 K. Upon saturating the TLFs in the substrate-free YIG at 20 mK, linewidths of 1.4 MHz are achievable: lower than those measured at room temperature.

cond-mat.mes-hall↗

arXiv2014

Photon-mediated interactions between distant artificial atoms

Photon-mediated interactions between atoms are of fundamental importance in quantum optics, quantum simulations and quantum information processing. The exchange of real and virtual photons between atoms gives rise to non-trivial interactions the strength of which decreases rapidly with distance in three dimensions. Here we study much stronger photon mediated interactions using two superconducting qubits in an open onedimensional transmission line. Making use of the unique possibility to tune these qubits by more than a quarter of their transition frequency we observe both coherent exchange interactions at an effective separation of $3λ/4$ and the creation of super- and sub-radiant states at a separation of one photon wavelength $λ$. This system is highly suitable for exploring collective atom/photon interactions and applications in quantum communication technology.

quant-ph↗