arXiv subjects

J. Clarke

Publications and source records attributed to J. Clarke.

At least 19 recordsLinked to original sources

arXiv2026

Spectral Data-cube Cleaning for CCAT Deep Spectroscopic Survey. I. Effect of correlated noise and filtering on the power spectrum

The Epoch of Reionization Spectrometer (EoR-Spec) on the Fred Young Submillimeter Telescope (FYST) will conduct the CCAT Deep Spectroscopic Survey (DSS) to perform line-intensity mapping of redshifted [C II] emission. Atmospheric $1/f$ noise and instrumental systematics affect power-spectrum recovery. We present realistic end-to-end simulations to quantify these effects and evaluate a Filter-and-Bin (F&B) pipeline. The simulated observations include instrument response, astrophysical emission, atmospheric noise, and observing strategy. The pipeline suppresses atmospheric $1/f$ noise by about four orders of magnitude at low temporal frequencies while leaving only minor residual correlated noise. For a single EoR-Spec module operating at 50% observing efficiency, the DSS is expected to detect the combined [C II] + CO power spectrum on shot-noise-dominated scales ($k > 0.1\,\mathrm{Mpc}^{-1}$). With two modules operating at full efficiency, detections are achievable over all targeted spatial scales. The transfer function exceeds 80% at $k \gtrsim 0.5\,\mathrm{Mpc}^{-1}$ but falls below 20% at $k \lesssim 0.1\,\mathrm{Mpc}^{-1}$, indicating significant suppression of large-scale modes. These results demonstrate that the F&B pipeline is effective for recovering the shot-noise regime, while improved map-making techniques will be required for accurate large-scale clustering measurements.

astro-ph.GA↗

arXiv2026

Testing masking effectiveness using multi-line image cubes based on COSMOS2020 for [CII] line intensity mapping at $z_{[CII]} > 3.5$

We created line intensity mapping intensity cubes for CO and [CII] emission lines using the COSMOS2020 galaxy catalogue, forming predictions based on empirical data, for observations from Prime-Cam mounted on the Fred Young Submm Telescope. We also included simulated noise including white and correlated components, and tested masking techniques to recover [CII] signal at $3.5<z<8.2$. We applied line luminosity models to the COSMOS2020 galaxy catalogue, spanning 1.44deg$^2$, to estimate the [CII] and CO J=1-0 emission, with other CO transitions derived using Spectral Line Energy Distribution templates. From these we made cubes for four 40 GHz bands in the EoR-Spec frequency range (205-420GHz), as well as a potential future upgrade to EoR-Spec including bands at 150 and 90GHz. Given the incompleteness of the empirical catalogue, these predictions are conservative lower limits, which we subsequently extrapolated from. We applied masks to recover the [CII] power spectra, using bright galaxies of COSMOS2020 as a foreground catalogue to target CO at low z (targeted masking), and matching bright voxels across frequency bands to eliminate those associated with CO emission (blind masking). Our CO intensity cube predictions are consistent with ALMA, VLA and NOEMA observations, indicating that this method gives realistic CO estimates for E-COSMOS. In ideal conditions, masking can recover [CII] above 300GHz, with targeted masking requiring a complete foreground catalogue of bright CO sources to prevent them from contributing to contaminant emission, and blind masking needing additional lower frequency ranges to be effective. However, noise will hinder [CII] recovery above 300 GHz until near the end of the currently planned 2000 hour observing period, as $S/N<5$ without extra observing time. Whilst CO can be recovered below 300GHz, [CII] will be unavailable without cross correlation techniques.

astro-ph.GA↗

arXiv2024

[CII] line intensity mapping the epoch of reionization with the Prime-Cam on FYST II. CO foreground masking based on an external catalog

Context. The Fred Young Submillimeter Telescope (FYST) line intensity mapping (LIM) survey will measure the power spectrum (PS) of the singly ionized carbon 158 $\rm \mu$m fine-structure line, [CII], to trace the appearance of the first galaxies that emerged during and right after the epoch of reionization (EoR, $6<z<9$). Aims. We aim to quantify the contamination of the (post-)EoR [CII] LIM signal by foreground carbon monoxide (CO) line emission ($3 < J_{ \rm up} < 12$) and assess the efficiency to retrieve this [CII] LIM signal by the targeted masking of bright CO emitters. Methods. Using the IllustrisTNG300 simulation, we produced mock CO intensity tomographies based on empirical star formation rate-to-CO luminosity relations. Combining these predictions with the [CII] PS predictions of the first paper of this series, we evaluated a masking technique where the interlopers are identified and masked using an external catalog whose properties are equivalent to those of a deep Euclid survey. Results. Prior to masking, our [CII] PS forecast is an order of magnitude lower than the predicted CO contamination in the 225 GHz ([CII] emitted at $z=6.8-8.3$) band of the FYST LIM survey, at the same level in its 280 GHz ([CII] emitted at $z=5.3-6.3$) and 350 GHz ([CII] emitted at $z=4.1-4.8$) bands, and an order of magnitude higher in its 410 GHz ([CII] emitted at $z=3.4-3.9$) band. For our fiducial model, the optimal masking depth is reached when less than 10\% of the survey volume is masked at 350 and 410 GHz but around 40\% at 280 GHz and 60 \% at 225 GHz. At these masking depths we anticipate a detection of the [CII] PS at 350 and 410 GHz, a tentative detection at 280 GHz, whereas at 225 GHz the CO signal still dominates our model. In the last case, alternative decontamination techniques will be needed.

astro-ph.GA↗

arXiv2024

The ionization yield in a methane-filled spherical proportional counter

Spherical proportional counters (SPCs) are gaseous particle detectors sensitive to single ionization electrons in their target media, with large detector volumes and low background rates. The $\mbox{NEWS-G}$ collaboration employs this technology to search for low-mass dark matter, having previously performed searches with detectors at the Laboratoire Souterrain de Modane (LSM), including a recent campaign with a 135 cm diameter SPC filled with methane. While in situ calibrations of the detector response were carried out at the LSM, measurements of the mean ionization yield and fluctuations of methane gas in SPCs were performed using a 30 cm diameter detector. The results of multiple measurements taken at different operating voltages are presented. A UV laser system was used to measure the mean gas gain of the SPC, along with $\mathrm{^{37}Ar}$ and aluminum-fluorescence calibration sources. These measurements will inform the energy response model of future operating detectors.

physics.ins-det↗

arXiv2024

Search for Light Dark Matter with NEWS-G at the Laboratoire Souterrain de Modane Using a Methane Target

The NEWS-G direct detection experiment uses spherical proportional counters to search for light dark matter candidates. New results from a 10 day physics run with a $135\,\mathrm{cm}$ in diameter spherical proportional counter at the Laboratoire Souterrain de Modane are reported. The target consists of $114\,\mathrm{g}$ of methane, providing sensitivity to dark matter spin-dependent coupling to protons. New constraints are presented in the mass range $0.17$ to $1.2\,\mathrm{GeV/c^2}$, with a 90% confidence level cross-section upper limit of $30.9\,\mathrm{pb}$ for a mass of $0.76\,\mathrm{GeV/c^2}$.

hep-ex↗

arXiv2024

[CII] luminosity models and large-scale image cubes based on COSMOS 2020 and ALPINE-ALMA [CII] data back to the epoch of reionisation

We have implemented a novel method to create simulated [CII] emission line intensity mapping (LIM) data cubes using COSMOS 2020 galaxy catalogue data. It allows us to provide solid lower limits for previous simulation-based model predictions and the expected signal strength of upcoming surveys. We applied [CII]158$\mu$m luminosity models to COSMOS 2020 to create LIM cubes covering a 1.2$\times$1.2 deg$^2$ sky area. These models were derived using galaxy bulk property data from the ALPINE-ALMA survey over the redshift range $4.4 1 when using FYST parameters. However, our high-redshift results remain inconclusive because of the poor completeness of COSMOS 2020 at $z$>6.3. These predictions will be improved on the basis of future JWST data.

astro-ph.GA↗

arXiv2023

Axion Dark Matter eXperiment: Run 1A Analysis Details

The ADMX collaboration gathered data for its Run 1A axion dark matter search from January to June 2017, scanning with an axion haloscope over the frequency range 645-680 MHz (2.66-2.81 ueV in axion mass) at DFSZ sensitivity. The resulting axion search found no axion-like signals comprising all the dark matter in the form of a virialized galactic halo over the entire frequency range, implying lower bound exclusion limits at or below DFSZ coupling at the 90% confidence level. This paper presents expanded details of the axion search analysis of Run 1A, including review of relevant experimental systems, data-taking operations, preparation and interpretation of raw data, axion search methodology, candidate handling, and final axion limits.

hep-ex↗

arXiv2023

Extraordinary physical properties of superconducting YBa$_{1.4}$Sr$_{0.6}$Cu$_3$O$_6$Se$_{0.51}$ in a multiphase ceramic material

We report on a novel material obtained by modifying pristine YBCO superconductor in solid phase synthesis via simultaneous partial substitution of Ba by Sr and O by Se. Simultaneous application of EDX and EBSD confirmed that Se atoms indeed enter the crystalline lattice cell. The detailed XRD analysis further confirmed this conclusion and revealed that the obtained polycrystalline material contains 5 phases, with the major phase ($>$30\%) being a cuprate YBa$_{1.4}$Sr$_{0.6}$Cu$_{3}$O$_{6}$Se$% _{0.51}$. The obtained superconductor demonstrates unique properties, including i) two superconducting transitions with $T_{c1}\approx$ 35 K (granular surface phase) and $T_{c2}\approx$ 13 K (bulk granular phase) - this granular phase arrangement naturally yields the Wohlleben effect; ii) reentrant diamagnetism and resistive state; iii) strong paramagnetism with Curie-Weiss behavior (% $\theta_{CW} \approx$ 4 K) and the ferromagnetic phase overruled by superconductivity; iv) Schottky anomaly visible in the heat capacity data and most likely delivered by small clusters of magnetic moments. Thorough analysis of the heat capacity data reveals a strong-coupling $d-$wave pairing in its bulk phase (with $2\Delta /T_{c}\approx 5$), and, most importantly, a very unusual anomaly in this cuprate. There are reasons to associate this anomaly with the quantum criticality observed in traditional cuprate superconductors at much higher fields (achievable only in certain laboratories). In our case, the fields leading to quantum criticality are much weaker ($\sim $7-9 T) thus opening avenues for exploration of the interplay between superconductivity and pair density waves by the wider research community.

cond-mat.supr-con↗

arXiv2023

A study of convective core overshooting as a function of stellar mass based on two-dimensional hydrodynamical simulations

We perform two-dimensional numerical simulations of core convection for zero-age-main-sequence stars covering a mass range from 3 $M_\odot$ to 20 $M_\odot$. The simulations are performed with the fully compressible time-implicit code MUSIC. We study the efficiency of overshooting, which describes the ballistic process of convective flows crossing a convective boundary, as a function of stellar mass and luminosity. We also study the impact of artificially increasing the stellar luminosity for 3 $M_\odot$ models. The simulations cover hundreds to thousands of convective turnover timescales. Applying the framework of extreme plume events previously developed for convective envelopes, we derive overshooting lengths as a function of stellar masses. We find that the overshooting distance ($d_{\rm ov}$) scales with the stellar luminosity ($L$) and the convective core radius ($r_{\rm conv}$). We derive a scaling law $d_{\rm ov} \propto L^{1/3} r_{\rm conv}^{1/2}$ which is implemented in a 1D stellar evolution code and the resulting stellar models are compared to observations. The scaling predicts values for the overshooting distance that significantly increase with stellar mass, in qualitative agreement with observations. Quantitatively, however, the predicted values are underestimated for masses $\gtrsim 10 M_\odot$. Our 2D simulations show the formation of a nearly-adiabatic layer just above the Schwarzschild boundary of the convective core, as exhibited in recent 3D simulations of convection. The most luminous models show a growth in size with time of the nearly-adiabatic layer. This growth seems to slow down as the upper edge of the nearly-adiabatic layer gets closer to the maximum overshooting length and as the simulation time exceeds the typical thermal diffusive timescale in the overshooting layer.

astro-ph.SR↗

arXiv2022

Effective circuit modelling and experimental realization of an ultra-compact self-rectifier flux pump

This paper presents experimental and modelling results of an ultra-compact self-rectifier flux pump energizing a superconducting coil. The device fits inside a volume of 65x65x50~mm and generates up to 320~A dc through the coil and a peak output voltage up to 60~mV. We also develop and present a full electromagnetic effective circuit model of the flux pump and compare its predictions to the experimental results. We show that our model can reproduce accurately the charging of the load coil and that it reproduces the systematic dependence of the maximum load coil current on the input current waveform. The experiments and modelling together show also the importance of dc-flux offsets in the transformer core on the final achievable current through the coil. The miniaturization possible for this class of flux pump and their minimal heat-leak into the cryogenic environment from thermal conduction make them attractive for applications with demanding size, weight and power limitations. Our effective circuit model is a useful tool in the understanding, design and optimization of such flux pumps which will accelerate their progression from research devices to their application.

cond-mat.supr-con↗

arXiv2021

Valley splitting in silicon from the interference pattern of quantum oscillations

We determine the energy splitting of the conduction-band valleys in two-dimensional (2D) electrons confined in silicon metal oxide semiconductor (Si-MOS) Hall-bar transistors. These Si-MOS Hall bars are made by advanced semiconductor manufacturing on 300 mm Si wafers and support a 2D electron gas of high quality with a maximum mobility of 17.6$\times$10$^3$cm$^2$/Vs and minimum percolation density of 3.45$\times$10$^{10}$cm$^{-2}$. Because of the low disorder, we observe beatings in the Shubnikov-de Haas oscillations that arise from the energy-split two low-lying conduction band valleys. From the analysis of the oscillations beating patterns up to T = 1.7 K, we estimate a maximum valley splitting of 8.2 meV at a density of 6.8$\times$10$^{12}$cm$^{-2}$. Furthermore, the valley splitting increases with density at a rate consistent with theoretical predictions for a near-ideal semiconductor/oxide interface.

cond-mat.mes-hall↗

arXiv2020

Generating mechanical and optomechanical entanglement via pulsed interaction and measurement

Entanglement generation at a macroscopic scale offers an exciting avenue to develop new quantum technologies and study fundamental physics on a tabletop. Cavity quantum optomechanics provides an ideal platform to generate and exploit such phenomena owing to the precision of quantum optics combined with recent experimental advances in optomechanical devices. In this work, we propose schemes operating outside the resolved-sideband regime, to prepare and verify both optical-mechanical and mechanical-mechanical entanglement. Our schemes employ pulsed interactions with a duration much less than the mechanical period and, together with homodyne measurements, can both generate and characterize these types of entanglement. To improve the performance of our schemes, a precooling stage comprising prior pulses can be utilized to increase the amount of entanglement prepared, and local optical squeezers may be used to provide resilience against open-system dynamics. The entanglement generated by our schemes is quantified using the logarithmic negativity and is analysed with respect to the strength of the pulsed optomechanical interactions for realistic experimental scenarios including mechanical decoherence and optical loss. Two separate schemes for mechanical entanglement generation are introduced and compared: one scheme based on an optical interferometric design, and the other comprising sequential optomechanical interactions. The pulsed nature of our protocols provides more direct access to these quantum correlations in the time domain, with applications including quantum metrology and tests of quantum decoherence. By considering a parameter set based on recent experiments, the feasibility to generate significant entanglement with our schemes, even with large optical losses, is demonstrated.

quant-ph↗

arXiv2019

Extended Search for the Invisible Axion with the Axion Dark Matter Experiment

This paper reports on a cavity haloscope search for dark matter axions in the galactic halo in the mass range $2.81$-$3.31$ $μeV$. This search excludes the full range of axion-photon coupling values predicted in benchmark models of the invisible axion that solve the strong CP problem of quantum chromodynamics, and marks the first time a haloscope search has been able to search for axions at mode crossings using an alternate cavity configuration. Unprecedented sensitivity in this higher mass range is achieved by deploying an ultra low-noise Josephson parametric amplifier as the first stage signal amplifier.

hep-ex↗

arXiv2019

Piezoelectrically Tuned Multimode Cavity Search for Axion Dark Matter

The $μ$eV axion is a well-motivated extension to the standard model. The Axion Dark Matter eXperiment (ADMX) collaboration seeks to discover this particle by looking for the resonant conversion of dark-matter axions to microwave photons in a strong magnetic field. In this Letter, we report results from a pathfinder experiment, the ADMX "Sidecar," which is designed to pave the way for future, higher mass, searches. This testbed experiment lives inside of and operates in tandem with the main ADMX experiment. The Sidecar experiment excludes masses in three widely spaced frequency ranges (4202-4249, 5086-5799, and 7173-7203 MHz). In addition, Sidecar demonstrates the successful use of a piezoelectric actuator for cavity tuning. Finally, this publication is the first to report data measured using both the TM$_{010}$ and TM$_{020}$ modes.

hep-ex↗

arXiv2018

Modulation Sensitive Search for Non-Virialized Dark-Matter Axions

Non-virialized dark-matter axions may be present in the Milky Way halo in the form of low-velocity-dispersion flows. The Axion Dark Matter eXperiment performed a search for the conversion of these axions into microwave photons using a resonant cavity immersed in a strong, static magnetic field. The spread of photon energy in these measurements was measured at spectral resolutions of the order of 1 Hz and below. If the energy variation were this small, the frequency modulation of any real axion signal due to the orbital and rotational motion of the Earth would become non-negligible. Conservative estimates of the expected signal modulation were made and used as a guide for the search procedure. The photon frequencies covered by this search are 812$-$852 and 858$-$892 MHz, which correspond to an axion mass of 3.36$-$3.52 and 3.55$-$3.69 μeV. No axion signal was found, and limits were placed on the maximum local density of non-virialized axions of these masses.

astro-ph.CO↗

arXiv2018

A Search for Invisible Axion Dark Matter with the Axion Dark Matter Experiment

This Letter reports results from a haloscope search for dark matter axions with masses between 2.66 and 2.81 $μ$eV. The search excludes the range of axion-photon couplings predicted by plausible models of the invisible axion. This unprecedented sensitivity is achieved by operating a large-volume haloscope at sub-kelvin temperatures, thereby reducing thermal noise as well as the excess noise from the ultra-low-noise SQUID amplifier used for the signal power readout. Ongoing searches will provide nearly definitive tests of the invisible axion model over a wide range of axion masses.

hep-ex↗

arXiv2017

Medical therapy and imaging fixed-field alternating-gradient accelerator with realistic magnets

NORMA is a design for a normal-conducting race track fixed-field alternating-gradient accelerator (FFAG) for protons from 50 to 350 MeV. In this article we show the development from an idealised lattice to a design implemented with field maps from rigorous two-dimensional (2D) and three-dimensional (3D) FEM magnet modelling. We show that whilst the fields from a 2D model may reproduce the idealised field to a close approximation, adjustments must be made to the lattice to account for differences brought about by the 3D model and fringe fields and full 3D models. Implementing these lattice corrections we recover the required properties of small tune shift with energy and a sufficiently-large dynamic aperture. The main result is an iterative design method to produce the first realistic design for a proton therapy accelerator that can rapidly deliver protons for both treatment and for imaging at up to 350 MeV. The first iteration is performed explicitly and described in detail in the text.

physics.acc-ph↗

arXiv2016

The Flux Qubit Revisited to Enhance Coherence and Reproducibility

The scalable application of quantum information science will stand on reproducible and controllable high-coherence quantum bits (qubits). Here, we revisit the design and fabrication of the superconducting flux qubit, achieving a planar device with broad frequency tunability, strong anharmonicity, high reproducibility, and relaxation times in excess of $40\,μ$s at its flux-insensitive point. Qubit relaxation times $T_1$ across 22 qubits are consistently matched with a single model involving resonator loss, ohmic charge noise, and 1/f flux noise, a noise source previously considered primarily in the context of dephasing. We furthermore demonstrate that qubit dephasing at the flux-insensitive point is dominated by residual thermal photons in the readout resonator. The resulting photon shot noise is mitigated using a dynamical decoupling protocol, resulting in $T_2\approx 85\,μ$s, approximately the $2T_1$ limit. In addition to realizing an improved flux qubit, our results uniquely identify photon shot noise as limiting $T_2$ in contemporary qubits based on transverse qubit-resonator interaction.

quant-ph↗