We present measurements of the E-mode polarization angular auto-power spectrum (EE) and temperature-E-mode cross-power spectrum (TE) of the cosmic microwave background (CMB) using 150 GHz data from ...three seasons of SPTpol observations. We report the power spectra over the spherical harmonic multipole range and detect nine acoustic peaks in the EE spectrum with high signal-to-noise ratio. These measurements are the most sensitive to date of the EE and TE power spectra at and , respectively. The observations cover 500 , a fivefold increase in area compared to previous SPTpol analyses, which increases our sensitivity to the photon diffusion damping tail of the CMB power spectra enabling tighter constraints on ΛCDM model extensions. After masking all sources with unpolarized flux mJy, we place a 95% confidence upper limit on residual polarized point-source power of at , suggesting that the EE damping tail dominates foregrounds to at least with modest source masking. We find that the SPTpol data set is in mild tension with the ΛCDM model ( ), and different data splits prefer parameter values that differ at the level. When fitting SPTpol data at , we find cosmological parameter constraints consistent with those for Planck temperature. Including SPTpol data at results in a preference for a higher value of the expansion rate ( ) and a lower value for present-day density fluctuations ( ).
The complex conductivity of a superconducting thin film is related to the quasiparticle density, which depends on the physical temperature and can also be modified by external pair breaking with ...photons and phonons. This relationship forms the underlying operating principle of Kinetic Inductance Detectors (KIDs), where the detection threshold is governed by the superconducting energy gap. We investigate the electromagnetic properties of thin-film aluminum that is proximitized with either a normal metal layer of copper or a superconducting layer with a lower <inline-formula><tex-math notation="LaTeX">T_{C}</tex-math></inline-formula>, such as iridium, in order to extend the operating range of KIDs. Using the Usadel equations along with the Nam expressions for complex conductivity, we calculate the density of states and the complex conductivity of the resulting bilayers to understand the dependence of the pair breaking threshold, surface impedance, and intrinsic quality factor of superconducting bilayers on the relative film thicknesses. The calculations and analyses provide theoretical insights in designing aluminum-based bilayer kinetic inductance detectors for detection of microwave photons and athermal phonons at the frequencies well below the pair breaking threshold of a pure aluminum film.
We present a measurement of the cosmic microwave background lensing potential using 500 deg2 of 150 GHz data from the SPTpol receiver on the South Pole Telescope. The lensing potential is ...reconstructed with signal-to-noise per mode greater than unity at lensing multipoles L 250, using a quadratic estimator on a combination of cosmic microwave background temperature and polarization maps. We report measurements of the lensing potential power spectrum in the multipole range of 100 < L < 2000 from sets of temperature-only (T), polarization-only (POL), and minimum-variance (MV) estimators. We measure the lensing amplitude by taking the ratio of the measured spectrum to the expected spectrum from the best-fit Λ cold dark matter model to the Planck 2015 TT + low P + lensing data set. For the minimum-variance estimator, we find A MV = 0.944 0.058 ( Stat . ) 0.025 ( Sys . ) ; restricting to only polarization data, we find A POL = 0.906 0.090 ( Stat . ) 0.040 ( Sys . ) . Considering statistical uncertainties alone, this is the most precise polarization-only lensing amplitude constraint to date (10.1 ) and is more precise than our temperature-only constraint. We perform null tests and consistency checks and find no evidence for significant contamination.
We present cosmological constraints based on the cosmic microwave background (CMB) lensing potential power spectrum measurement from the recent 500 deg2 SPTpol survey, the most precise CMB lensing ...measurement from the ground to date. We fit a flat ΛCDM model to the reconstructed lensing power spectrum alone and in addition with other data sets: baryon acoustic oscillations (BAO), as well as primary CMB spectra from Planck and SPTpol. The cosmological constraints based on SPTpol and Planck lensing band powers are in good agreement when analyzed alone and in combination with Planck full-sky primary CMB data. With weak priors on the baryon density and other parameters, the SPTpol CMB lensing data alone provide a 4% constraint on . Jointly fitting with BAO data, we find , , and , up to away from the central values preferred by Planck lensing + BAO. However, we recover good agreement between SPTpol and Planck when restricting the analysis to similar scales. We also consider single-parameter extensions to the flat ΛCDM model. The SPTpol lensing spectrum constrains the spatial curvature to be and the sum of the neutrino masses to be eV at 95% C.L. (with Planck primary CMB and BAO data), in good agreement with the Planck lensing results. With the differences in the signal-to-noise ratio of the lensing modes and the angular scales covered in the lensing spectra, this analysis represents an important independent check on the full-sky Planck lensing measurement.
A superconducting film with a tunable low transition temperature (Tc) is required in high-resolution Transition-Edge Sensor (TES) detectors, which have applications including dark matter detection, ...low threshold coherent elastic neutrino nucleus scattering measurement, and X-ray spectroscopy. We have been investigating a new approach to tune the Tc of superconducting thin films fabricated by co-sputtering Iridium and Platinum. The effects of Pt concentration and deposition parameters on the films' structural, electrical, and superconducting properties have been studied. AFM and XRD techniques and low temperature resistance measurements have been utilized for film characterization. By varying the Pt concentration and deposition parameters when co-sputtering, we have successfully achieved controllable tuning of Tc in the range of 30–200 mK. The experimental results demonstrate co-sputtering as a viable method for controlling the Tc of Ir-based thin films that can be applied to fabricating high-resolution TESs.
Direct detection of nuclear scatterings of sub-GeV dark matter (DM) particles favors low-Z nuclei. Hydrogen nucleus, which has a single proton, provides the best kinematic match. The characteristic ...nuclear recoil energy is boosted by a factor of a few tens from those for larger nuclei used in traditional Weakly Interacting Massive Particles searches. Furthermore, hydrogen is optimal for detecting spin-dependent nuclear scatterings of sub-GeV DM, where large parameter space still remains unconstrained yet. In this paper, we first introduce several hydrogen-rich targets, which emit two classes of signals under kinetic excitations. One class of the signals is infrared photons, which are from fundamental vibrational and rotational modes of molecules and at several characteristic wavelengths. Another is acoustic phonons and optical phonons that decay into acoustic phonons. We then discuss the technical status and future researches of low-
T
c
transition-edge sensor (TES) detectors, which measure the infrared photons and acoustic phonons with desirable sensitivities. Utilization of hydrogen-rich targets and ultra-sensitive low-
T
c
TES detectors for light DM detection requires both theoretical modeling and experimental prototyping.
A microwave kinetic inductance detector (MKID) is a superconducting pair breaking detector that offers a number of unique advantages for realizing large-format arrays of ultra-sensitive detectors, ...such as inherent multiplexibility and relative ease of fabrication. With the detection threshold being set by the Cooper pair binding energy, and correspondingly, the superconducting critical temperature (
T
c
), typically well-understood MKID materials such as aluminum (Al) present a lower limit on the operating frequency. Aluminum manganese (Al-Mn) is a promising candidate material for MKIDs because it can be fabricated with nearly identical processing as pure Al, but allows for control of the
T
c
with varying levels of Mn doping or post-deposition heat treatment. We present initial results from an early characterization of AlMn using a series of lumped-element superconducting microwave resonators, including measurements of
T
c
, internal quality factor, and noise performance over a range of Mn doping.
We have measured the quasiparticle generation-recombination (GR) noise in aluminium lumped element kinetic inductors with a wide range of detector volumes at various temperatures. The basic detector ...consists of meandering inductor and interdigitated capacitor fingers. The inductor volume is varied from 2 to 153 <inline-formula><tex-math notation="LaTeX">\mu \mathrm{m}^{3}</tex-math></inline-formula> by changing the inductor width and length to maintain a constant inductance. We started with measuring the power spectrum density (PSD) of the detectors frequency noise which is a function of GR noise and we clearly observed the spectrum roll off at 10 kHz which corresponds to the quasiparticle lifetime. Using data from a temperature sweep of the resonator frequency we convert the frequency fluctuation to quasiparticle fluctuation and observe its strong dependence on detector volume: detectors with smaller volume display less quasiparticle noise amplitude. Meanwhile we observe a saturated quasiparticle density at low temperature from all detectors as the quasiparticle life time <inline-formula><tex-math notation="LaTeX">\boldsymbol{\tau _{qp}}</tex-math></inline-formula> approaches a constant value at low temperature.
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