arXiv subjects

Ben T. McAllister

Publications and source records attributed to Ben T. McAllister.

At least 19 recordsLinked to original sources

arXiv2026

Foil-Mediated Mutual-Impedance in Microwave Cavities with Enhanced Phase Response

We formulate and validate an equivalent circuit model describing mutual coupling between three microwave cavity resonators interconnected via thin metallic foils. Each cavity is represented as a lumped LCR circuit, while the foils act as interfaces that mediate energy exchange via mutual impedance. This coupling mechanism produces interference effects and a controllable antiresonance when the input resonators are amplitude- and phase-balanced, while enabling coupling across a continuous metallic interface without direct antenna or aperture coupling. All three resonators operated in the TM$_{010}$ mode, where two input resonators each excited the third via a thin copper foil. Analytical expressions are derived for the mutual impedance and coupling coefficient of these foils in this geometry. Under balanced conditions, a sharp antiresonance emerges with a several-fold enhanced phase sensitivity at the resonant frequency of the output cavity, consistent with model predictions. The experimentally extracted normalised mutual coupling coefficients, $Δ_{13}=(10.8\pm0.3)\times10^{-6}$ and $Δ_{23}=(8.6\pm0.2)\times10^{-6}$, fall within the calculated range $Δ_{n3}\approx(7\text{--}17)\times10^{-6}$ derived from the foil's electromagnetic properties, where the spread is dominated by the estimated foil thickness uncertainty of $(8.9\pm0.4)\,μ\mathrm{m}$. These results demonstrate a foil-mediated physical implementation of weak mutual coupling across a metallic interface spanning multiple skin depths, providing a distinct route for engineering controlled interference in three-dimensional multi-resonator systems.

physics.app-ph↗

arXiv2026

A Search for Effects of Cosmic Rays with Multi-scale Entropy Metrics

We report a comparison of frequency fluctuations in oven-controlled quartz bulk-acoustic-wave oscillators operated above ground and one kilometre underground in a low-muon-background environment. The experiment is motivated by the possibility that cosmic rays and other ionizing-radiation backgrounds produce rare, impulsive energy-deposition events that perturb high-Q mechanical resonators and appear as intermittent, non-Gaussian structure in oscillator frequency noise. Conventional power spectral density and Allan-deviation analyses show no statistically compelling separation between the two environments over the explored timescales. In contrast, multi-scale sample entropy and its modified form reveal a pronounced divergence, with the underground data exhibiting increased predictability over a broad range of effective integration times. This result identifies a change in the temporal structure of the oscillator fluctuations that is largely hidden from standard second-order frequency-stability metrics. We therefore propose multi-scale sample entropy as a new diagnostic for frequency control and timing, complementary to Allan deviation and spectral analysis, with particular sensitivity to intermittent structure, non-stationary contributions, and rare-event contamination. The observed entropy separation also provides evidence that the above-ground cosmic-ray environment influences oscillator frequency fluctuations, suggesting that radiation-linked disturbances may contribute to the stochastic behaviour of precision mechanical oscillators. These findings introduce an entropy-based methodology for oscillator metrology and provide a practical tool for future fundamental-physics experiments using cryogenic resonant sensors, where rare-event backgrounds and poorly understood low-frequency noise can limit sensitivity.

physics.ins-det↗

arXiv2026

Optimising Re-entrant Cavity Designs for Low Mass Axion Haloscopes

Axion haloscopes provide a leading experimental approach to detecting QCD axion dark matter through resonant axion-photon conversion in microwave cavities. Extending haloscope sensitivity to low axion masses remains challenging due to the large resonator volumes required at sub-GHz frequencies. Re-entrant cavities offer a compact solution, but their performance depends strongly on geometric optimisation. We present a comprehensive finite-element study of re-entrant cavity haloscope designs operating in the 100 to 500 MHz range, comparing their performance using effective scan time as a figure of merit. Among the configurations studied, we identify a double attack geometry that achieves a roughly threefold improvement in effective scan time compared to a conventional single-rod re-entrant cavity. We further investigate practical implementation strategies, including a hybrid design employing one fixed rod and one tunable rod, which preserves a scan time gain while reducing mechanical complexity. These results demonstrate a pathway to enhanced low-mass axion haloscope sensitivity.

physics.ins-det↗

arXiv2025

Follow-up Search for a Tentative Dark Photon Signal Near 19.5 $μ$eV using ORGAN-Q infrastructure

A recent independent dark photon (DP) focused reanalysis of existing data from the TASEH axion haloscope experiment reported a tentative DP dark matter signal with local significance $\sim 4.7σ$ at $f_X \simeq$ 4.71 GHz, corresponding to $m_X \simeq 19.5~μ$eV and kinetic mixing $ε\sim 6.5\times 10^{-15}$. Motivated by this report, we performed a dedicated, narrowband follow-up experiment to confirm or refute the signal with a cryogenic microwave cavity operated \emph{without} a magnetic field, leveraging the ORGAN-Q dilution refrigeration and receiver chain. Scanning a window centered on the reported frequency over a live time of $T_{int}\sim 13$ days, we find no excess consistent with a dark photon signal as reported, and set $95\%$ C.L. exclusion on $ε$ in a narrow mass range around $\sim 19.5~μ$eV, excluding a signal of the strength and frequency reported to 99.92$\%$ confidence. We discuss the experiment and present the exclusion limits.

hep-ex↗

arXiv2025

Near-quantum-limited axion dark matter search with the ORGAN experiment around 26 $μ$eV

The latest result from the ORGAN experiment, an axion haloscope is presented. This iteration of the experiment operated at millikelvin temperatures using a flux-driven Josephson parametric amplifier for reduced noise, along with various other improvements over previous iterations. Covering the $25.45 - 26.27\,μ\text{eV}$ ($6.15-6.35$ GHz) mass (frequency) range, this near-quantum limited phase of ORGAN employs a conducting rod resonator and a 7-T solenoidal magnet to place the most sensitive exclusion limits on axion-photon coupling in the range to date, with $|g_{aγγ}| \gtrsim 2.8\times10^{-13}$ at a 95\% confidence level.

hep-ex↗

arXiv2024

Conductivity Freeze-Out in Isotopically Pure Si-28 at milli-Kelvin Temperatures

Silicon is a key semiconducting material for electrical devices and hybrid quantum systems where low temperatures and zero-spin isotopic purity can enhance quantum coherence. Electrical conductivity in Si is characterised by carrier freeze out at around 40 K allowing microwave transmission which is a key component for addressing spins efficiently in silicon quantum technologies. In this work, we report an additional sharp transition of the electrical conductivity in a Si-28 cylindrical cavity at around 1 Kelvin. This is observed by measuring microwave resonator Whispering Gallery Mode frequencies and Q factors with changing temperature and comparing these results with finite element models. We attribute this change to a transition from a relaxation mechanism-dominated to a resonant phonon-less absorption-dominated hopping conduction regime. Characterising this regime change represents a deeper understanding of a physical phenomenon in a material of high interest to the quantum technology and semiconductor device community and the impact of these results is discussed.

cond-mat.mtrl-sci↗

arXiv2023

Exclusion of ALP Cogenesis Dark Matter in a Mass Window Above 100 $μ$eV

We report the results of Phase 1b of The ORGAN Experiment, a microwave cavity haloscope searching for dark matter axions in the $107.42-111.93~μ$eV mass range. The search excludes axions with two-photon coupling $g_{aγγ}\geq 4\times 10^{-12}\, \textrm{GeV}^{-1}$ with $95\%$ confidence interval, setting the best upper bound to date and with the required sensitivity to exclude the axion-like particle cogenesis model for dark matter in this range. This result was achieved using a tunable rectangular cavity, which mitigated several practical issues that become apparent when conducting high mass axion searches, and was the first such axion search to be conducted with such a cavity. It also represents the most sensitive axion haloscope experiment to date in the $\sim100~μ$eV mass region.

hep-ex↗

arXiv2023

Tunable Rectangular Resonant Cavities for Axion Haloscopes

Axions are a compelling dark matter candidate, and one of the primary techniques employed to search for them is the axion haloscope, in which a resonant cavity is deployed inside a strong magnetic field so that some of the surrounding axions may convert into photons via the inverse Primakoff effect and become trapped inside the resonator. Resonant cavity design is critical to the sensitivity of a haloscope, and several geometries have been utilised and proposed. Here we consider a relatively simple concept - a rectangular resonant cavity with a tunable wall - and compare it to the standard tuning rod-type resonators employed in the field. We find that the rectangular cavities support similar modes to cylindrical tuning rod cavities, and have some advantages in terms of axion sensitivity and practicality, particularly when moving to higher frequencies which are of great and growing interest in the international axion dark matter community.

physics.ins-det↗

arXiv2023

Searching for Low-Mass Axions using Resonant Upconversion

We present new results of a room temperature resonant AC haloscope, which searches for axions via photon upconversion. Traditional haloscopes require a strong applied DC magnetic background field surrounding the haloscope cavity resonator, the resonant frequency of which is limited by available bore dimensions. UPLOAD, the UPconversion Low-Noise Oscillator Axion Detection experiment, replaces this DC magnet with a second microwave background resonance within the detector cavity, which upconverts energy from the axion field into the readout mode, accessing axions around the beat frequency of the modes. Furthermore, unlike the DC case, the experiment is sensitive to a newly proposed quantum electromagnetodynamical axion coupling term $g_{aBB}$. Two experimental approaches are outlined - one using frequency metrology, and the other using power detection of a thermal readout mode. The results of the power detection experiment are presented, which allows exclusion of axions of masses between 1.12 $-$ 1.20 $μeV$ above a coupling strength of both $g_{aγγ}$ and $g_{aBB}$ at $3 \times 10^{-6}$ 1/GeV, after a measurement period of 30 days, which is a three order of magnitude improvement over our previous result.

hep-ex↗

arXiv2022

Limits on Dark Photons, Scalars, and Axion-Electromagnetodynamics with The ORGAN Experiment

Axions are a well-motivated dark matter candidate, with a host of experiments around the world searching for direct evidence of their existence. The ORGAN Experiment is a type of axion detector known as an axion haloscope, which takes the form of a cryogenic resonant cavity embedded in a strong magnetic field. ORGAN recently completed Phase 1a, a scan for axions around 65 \textmu eV, and placed the most stringent limits to date on the dark matter axion-photon coupling in this region, $|g_{aγγ}|\leq 3\times 10^{-12}$. It has been shown that axion haloscopes such as ORGAN are automatically sensitive to other kinds of dark matter candidates, such as dark photons, scalar field/dilaton dark matter, and exotic axion-electromagnetic couplings motivated by quantum electromagnetodynamics. We compute the exclusion limits placed on these various dark matter candidates by ORGAN 1a, and project sensitivity for some future ORGAN phases. In particular, the dark photon limits are the most sensitive to date in some regions of the parameter space.

hep-ph↗

arXiv2022

Direct Search for Dark Matter Axions Excluding ALP Cogenesis in the 63-67 micro-eV Range, with The ORGAN Experiment

The standard model axion seesaw Higgs portal inflation (SMASH) model is a well motivated, self-contained description of particle physics over a range of energy scales that predicts axion dark matter particles to exist within the mass range of $50-200\,μ$eV. To scan these masses an axion haloscope under a strong constant magnetic field must operate between 12 to 48 GHz. The ORGAN experiment (situated in Perth, Australia) is a microwave cavity axion haloscope that aims to search the majority of the mass range predicted by the SMASH model. Here we present results of Phase 1a, the first experiment to scan and search for axions in the microwave Ku Band. Our initial scan sets a new limit on the coupling of axions to two photons of $g_{aγγ}\geq 3\times 10^{-12}\, \textrm{GeV}^{-1}$ over the mass range $63.2$ to $67.1~μ$eV with $95\%$ confidence. This result is the most sensitive to date in this mass range, sufficient to exclude the well motivated ALP (Axion Like Particle) cogenesis model for dark matter, which adds ALPs to the standard model in the early universe to simultaneously explain the observed baryon and dark matter densities. To attain this level of sensitivity we utilised a TM$_{010}$ cylindrical cavity resonator, scanned between 15.28 to 16.23 GHz through the utilisation of a tuning rod. Measurements were performed over a duration of 3.5 weeks with a $74\%$ duty cycle, with the resonator coupled to a low noise HEMT amplifier and placed inside a superconducting solenoidal electromagnet of 11.5 Tesla in magnetic field strength.

hep-ex↗

arXiv2021

UPconversion Loop Oscillator Axion Detection experiment: A precision frequency interferometric axion dark matter search with a Cylindrical Microwave Cavity

First experimental results from a room-temperature table-top phase-sensitive axion haloscope experiment are presented. The technique exploits the axion-photon coupling between two photonic resonator-oscillators excited in a single cavity, allowing low-mass axions to be upconverted to microwave frequencies, acting as a source of frequency modulation on the microwave carriers. This new pathway to axion detection has certain advantages over the traditional haloscope method, particularly in targeting axions below 1 $μ$eV (240 MHz) in energy where high volume magnets are necessary. At the heart of the dual-mode oscillator, a tunable cylindrical microwave cavity supports a pair of orthogonally polarized modes ($\text{TM}_{\text{0,2,0}}$ and $\text{TE}_{\text{0,1,1}}$), which, in general, enables simultaneous sensitivity to axions with masses corresponding to the sum and difference of the microwave frequencies. The results place axion exclusion limits between 7.44 - 19.38 neV, excluding a minimal coupling strength above $3\times 10^{-3}$ 1/GeV, and between 74.4 - 74.5 $μ$eV, excluding a minimal coupling strength above $10^{-2}$ 1/GeV, after a measurement period of two and a half hours. We show that a state-of-the-art frequency-stabilized cryogenic implementation of this technique may achieve competitive limits in a large range of axion-space.

hep-ex↗

arXiv2021

Searching for Scalar Dark Matter via Coupling to Fundamental Constants with Photonic, Atomic and Mechanical Oscillators

We present a way to search for light scalar dark matter (DM), seeking to exploit putative coupling between dark matter scalar fields and fundamental constants, by searching for frequency modulations in direct comparisons between frequency stable oscillators. Specifically we compare a Cryogenic Sapphire Oscillator (CSO), Hydrogen Maser (HM) atomic oscillator and a bulk acoustic wave quartz oscillator (OCXO). This work includes the first calculation of the dependence of acoustic oscillators on variations of the fundamental constants, and demonstration that they can be a sensitive tool for scalar DM experiments. Results are presented based on 16 days of data in comparisons between the HM and OCXO, and 2 days of comparison between the OCXO and CSO. No evidence of oscillating fundamental constants consistent with a coupling to scalar dark matter is found, and instead limits on the strength of these couplings as a function of the dark matter mass are determined. We constrain the dimensionless coupling constant $d_e$ and combination $|d_{m_e}-d_g|$ across the mass band $4.4\times10^{-19}\lesssim m_φ\lesssim 6.8\times10^{-14}\:\text{eV} c^{-2}$, with most sensitive limits $d_e\gtrsim1.59\times10^{-1}$, $|d_{m_e}-dg|\gtrsim6.97\times10^{-1}$. Notably, these limits do not rely on Maximum Reach Analysis (MRA), instead employing the more general coefficient separation technique. This experiment paves the way for future, highly sensitive experiments based on state-of-the-art acoustic oscillators, and we show that these limits can be competitive with the best current MRA-based exclusion limits.

hep-ex↗

arXiv2021

Searching for dark matter with an unequal delay interferometer

We propose a new type of experiment that compares the frequency of a clock (an ultra-stable optical cavity in this case) at time $t$ to its own frequency some time $t-T$ earlier, by "storing" the output signal (photons) in a fibre delay line. In ultra-light oscillating dark matter (DM) models, such an experiment is sensitive to coupling of DM to the standard model fields, through oscillations of the cavity and fibre lengths and of the fibre refractive index. Additionally, the sensitivity is significantly enhanced around the mechanical resonances of the cavity. We present experimental result of such an experiment and report no evidence of DM for masses in the [$4.1\times 10^{-11}$, $8.3\times 10^{-10}$]~eV region. In addition, we improve constraints on the involved coupling constants by one order of magnitude in a standard galactic DM model, at the mass corresponding to the resonant frequency of our cavity. Furthermore, in the model of relaxion DM, we improve on existing constraints over the whole DM mass range by about one order of magnitude, and up to six orders of magnitude at resonance.

gr-qc↗

arXiv2021

The Electrodynamics of Free and Bound Charge Electricity Generators using Impressed Sources and the Modification to Maxwell's Equations

The conversion of external energy into electricity is the foundation of power station and energy harvesting operation. The external source supplies an impressed force per unit charge to free or bound charge to produces AC electricity. We analyze the electrodynamics of ideal electricity generators through a time dependent permanent polarization without any applied electric field, which modifies the constitutive relations and is essential to oscillate charge in a lossless way. For both cases, we show that Maxwell's equations, and in particular Faraday's law are modified, along with the required boundary conditions through the addition of an effective impressed magnetic current boundary source. For the free charge case, we highlight the example of an electromagnetic generator based on Lorentz force, where the impressed force per unit charge that polarizes the conductor comes from mechanical motion of free charge with an impressed velocity of a conductor relative to a stationary DC magnetic field. The bound charge generator is an idealized permanently polarized bar electret with a time dependent permanent polarization, the underlying principle behind piezoelectric nano-generators. In the open circuit state, both electricity generators are equivalent to idealized Hertzian dipoles, with the open circuit voltage equal to the induced emf. Analyzing the short circuit responses, we show that the bound charge electricity generator has a capacitive source impedance. In contrast, we show for the ideal free charge AC electricity generator, the back emf from the inductance of the loop that defines the short circuit, directly cancels the source emf, so the voltage across the inductor is solely determined by the magnetic current boundary source. Thus, we determine the magnetic current boundary source is the topological invariant that best describes the output voltage of an AC generator.

physics.class-ph↗

arXiv2020

Dielectric-Boosted Sensitivity to Cylindrical Azimuthally Varying Transverse-Magnetic Resonant Modes in an Axion Haloscope

Axions are a popular dark matter candidate which are often searched for in experiments known as ``haloscopes" which exploit a putative axion-photon coupling. These experiments typically rely on Transverse Magnetic (TM) modes in resonant cavities to capture and detect photons generated via axion conversion. We present a study of a resonant cavity design for application in haloscope searches, of particular use in the push to higher mass axion searches (above $\sim$60$\,μ$eV). In particular, we take advantage of azimuthally varying TM$_{m10}$ modes which, whilst typically insensitive to axions due to field non-uniformity, can be made axion-sensitive (and frequency tunable) through strategic placement of dielectric wedges, becoming a type of resonator known as a Dielectric Boosted Axion Sensitivity (DBAS) resonator. Results from finite-element modelling are presented, and compared with a simple proof-of-concept experiment. The results show a significant increase in axion sensitivity for these DBAS resonators over their empty cavity counterparts, and high potential for application in high mass axion searches when benchmarked against simpler, more traditional designs relying on fundamental TM modes.

physics.ins-det↗

arXiv2020

Broadband Electrical Action Sensing Techniques with conducting wires for low-mass dark matter axion detection

Due to the inverse Primakoff effect it has been shown that when axions interact with a DC magnetic B-field the resulting electrical action will produce an AC electromotive force which oscillates at the Compton frequency of the axion, and may be modeled as an oscillating effective impressed magnetic current boundary source. We use this result to calculate the sensitivity of new experiments to low-mass axions using the quasi-static technique. First, we calculate the current induced in an electric dipole antenna (straight conducting wire) when the DC B-field is spatially constant and show that it has a sensitivity proportional to the axion mass. Following this we extend the topology by making use of the full extent of the spatially varying DC B-field. This extension is achieved by transforming the 1D conducting wire to a 2D winding, to fully link the effective magnetic current boundary source and thus couple to the full axion induced electrical action. In this case the conductor becomes a coil winding where the voltage induced across the winding increases proportionally to the number of windings. We investigate two different topologies: The 1st uses a single winding, and couples to the effective short circuit current generated in the winding, which is read out using a sensitive low impedance SQUID amplifier: The 2nd uses multiple windings, with every turn effectively increasing the the voltage output proportional to the winding number. The read out of this configuration is optimised by implementing a cryogenic low-noise high input impedance voltage amplifier. The end result is a new Broadband Electrical Action Sensing Techniques with orders of magnitude improved sensitivity, which is linearly proportional to the axion photon coupling and capable of detecting QCD dark matter axions.

physics.ins-det↗

arXiv2020

Characterisation of Cryogenic Material Properties of 3D-Printed Superconducting Niobium using a 3D Lumped Element Microwave Cavity

We present an experimental characterisation of the electrical properties of 3D-printed Niobium. The study was performed by inserting a 3D-printed Nb post inside an Aluminium cylindrical cavity, forming a 3D lumped element re-entrant microwave cavity resonator. The resonator was cooled to temperatures below the critical temperature of Niobium (9.25K) and then Aluminium (1.2K), while measuring the quality factors of the electromagnetic resonances. This was then compared with finite element analysis of the cavity and a measurement of the same cavity with an Aluminium post of similar dimensions and frequency, to extract the surface resistance of the Niobium post. The 3D-printed Niobium exhibited a transition to the superconducting state at a similar temperature to the regular Niobium, as well as a surface resistance of $3.1\times10^{-4}$ $Ω$. This value was comparable to many samples of traditionally machined Niobium previously studied without specialised surface treatment. Furthermore, this study demonstrates a simple new method for characterizing the material properties of a relatively small and geometrically simple sample of superconductor, which could be easily applied to other materials, particularly 3D-printed materials. Further research and development in additive manufacturing may see the application of 3D-printed Niobium in not only superconducting cavity designs, but in the innovative technology of the future.

physics.app-ph↗