261 research outputs found
Current distribution and transition width in superconducting transition-edge sensors
Present models of the superconducting-to-normal transition in transition-edge
sensors (TESs) do not describe the current distribution within a biased TES.
This distribution is complicated by normal-metal features that are integral to
TES design. We present a model with one free parameter that describes the
evolution of the current distribution with bias. To probe the current
distribution experimentally, we fabricated TES devices with different current
return geometries. Devices where the current return geometry mirrors current
flow within the device have sharper transitions, thus allowing for a direct
test of the current-flow model. Measurements from these devices show that
current meanders through a TES low in the resistive transition but flows across
the normal-metal features by 40% of the normal-state resistance. Comparison of
transition sharpness between device designs reveals that self-induced magnetic
fields play an important role in determining the width of the superconducting
transition. [http://dx.doi.org/10.1063/1.4771984]Comment: 5 pages, 4 figure
The Practice of Pulse Processing
The analysis of data from x-ray microcalorimeters requires great care; their
excellent intrinsic energy resolution cannot usually be achieved in practice
without a statistically near-optimal pulse analysis and corrections for
important systematic errors. We describe the essential parts of a
pulse-analysis pipeline for data from x-ray microcalorimeters, including steps
taken to reduce systematic gain variation and the unwelcome dependence of
filtered pulse heights on the exact pulse-arrival time. We find these steps
collectively to be essential tools for getting the best results from a
microcalorimeter-based x-ray spectrometer.Comment: Accepted for publication in J. Low Temperature Physics, special issue
for the proceedings of the Low Temperature Detectors 16 conferenc
Approaches to the Optimal Nonlinear Analysis of Microcalorimeter Pulses
We consider how to analyze microcalorimeter pulses for quantities that are
nonlinear in the data, while preserving the signal-to-noise advantages of lin-
ear optimal filtering. We successfully apply our chosen approach to compute the
electrothermal feedback energy deficit (the "Joule energy") of a pulse, which
has been proposed as a linear estimator of the deposited photon energy.Comment: Accepted by Journal of Low Temperature Physics. Contribution to the
proceedings of Low Temperature Detectors 17, (Kurume Japan, 2017
Filters for High Rate Pulse Processing
We introduce a filter-construction method for pulse processing that differs
in two respects from that in standard optimal filtering, in which the average
pulse shape and noise-power spectral density are combined to create a
convolution filter for estimating pulse heights. First, the proposed filters
are computed in the time domain, to avoid periodicity artifacts of the discrete
Fourier transform, and second, orthogonality constraints are imposed on the
filters, to reduce the filtering procedure's sensitivity to unknown baseline
height and pulse tails. We analyze the proposed filters, predicting energy
resolution under several scenarios, and apply the filters to high-rate pulse
data from gamma-rays measured by a transition-edge-sensor microcalorimeter.Comment: 5 pages, 6 figures, 1 tabl
Insensitivity of sub-Kelvin electron-phonon coupling to substrate properties
We have examined the role of the substrate on electron-phonon coupling in
normal metal films of Mn-doped Al at temperatures below 1 K. Normal
metal-insulator-superconductor junctions were used to measure the electron
temperature in the films as a function of Joule heating power and phonon
temperature. Theory suggests that the distribution of phonons available for
interaction with electrons in metal films may depend on the acoustic properties
of the substrate, namely, that the electron-phonon coupling constant Sigma
would be larger on the substrate with smaller sound speed. In contrast, our
results indicate that within experimental error (typically +/- 10%), Sigma is
unchanged among the two acoustically distinct substrates used in our
investigation.Comment: 4 pages, 2 figures. Version 2 contains changes reflected in the final
published articl
Energy calibration of nonlinear microcalorimeters with uncertainty estimates from Gaussian process regression
The nonlinear energy response of cryogenic microcalorimeters is usually
corrected through an empirical calibration. X-ray or gamma-ray emission lines
of known shape and energy anchor a smooth function that generalizes the
calibration data and converts detector measurements to energies. We argue that
this function should be an approximating spline. The theory of Gaussian process
regression makes a case for this functional form. It also provides an important
benefit previously absent from our calibration method: a quantitative
uncertainty estimate for the calibrated energies, with lower uncertainty near
the best-constrained calibration points.Comment: Submitted to J. Low Temperature Physics for the Proceedings of the
19th International Workshop on Low-Temperature Detectors (2021
A three-wave mixing kinetic inductance traveling-wave amplifier with near-quantum-limited noise performance
We present a theoretical model and experimental characterization of a
microwave kinetic inductance traveling-wave amplifier (KIT), whose noise
performance, measured by a shot-noise tunnel junction (SNTJ), approaches the
quantum limit. Biased with a dc current, the KIT operates in a three-wave
mixing fashion, thereby reducing by several orders of magnitude the power of
the microwave pump tone and associated parasitic heating compared to
conventional four-wave mixing KIT devices. It consists of a 50 Ohms artificial
transmission line whose dispersion allows for a controlled amplification
bandwidth. We measure dB of gain across a 2 GHz bandwidth
with an input 1 dB compression power of -63 dBm, in qualitative agreement with
theory. Using a theoretical framework that accounts for the SNTJ-generated
noise entering both the signal and idler ports of the KIT, we measure the
system-added noise of an amplification chain that integrates the KIT as the
first amplifier. This system-added noise, quanta (equivalent to
K) between 3.5 and 5.5 GHz, is the one that a device replacing
the SNTJ in that chain would see. This KIT is therefore suitable to read large
arrays of microwave kinetic inductance detectors and promising for multiplexed
superconducting qubit readout
Optimization and analysis of code-division multiplexed TES microcalorimeters
We are developing code-division multiplexing (CDM) systems for
transition-edge sensor arrays with the goal of reaching multiplexing factors in
the hundreds. We report on x-ray measurements made with a four-channel
prototype CDM system that employs a flux-summing architecture, emphasizing
data-analysis issues. We describe an empirical method to determine the
demodulation matrix that minimizes cross-talk. This CDM system achieves energy
resolutions of between 2.3 eV and 3.0 eV FWHM at 5.9 keV.Comment: 7 pages, 5 figures. Presented at the 14th International Workshop on
Low Temperature Detectors, Heidelberg University, August 1-5, 2011,
proceedings to be published in the Journal of Low Temperature Physic
Superconducting micro-resonator arrays with ideal frequency spacing and extremely low frequency collision rate
We present a wafer trimming technique for producing superconducting
micro-resonator arrays with highly uniform frequency spacing. With the
light-emitting diode (LED) mapper technique demonstrated previously, we first
map the measured resonance frequencies to the physical resonators. Then, we
fine-tune each resonator's frequency by lithographically trimming a small
length, calculated from the deviation of the measured frequency from its design
value, from the interdigitated capacitor. We demonstrate this technique on a
127-resonator array made of titanium-nitride (TiN) and show that the uniformity
of frequency spacing is greatly improved. The array yield in terms of frequency
collisions improves from 84% to 97%, while the quality factors and noise
properties are unaffected. The wafer trimming technique provides an
easy-to-implement tool to improve the yield and multiplexing density of large
resonator arrays, which is important for various applications in photon
detection and quantum computing.Comment: 5 pages,4 figure
A Highly Linear Calibration Metric for TES X-ray Microcalorimeters
Transition-edge sensor X-ray microcalorimeters are usually calibrated
empirically, as the most widely-used calibration metric, optimal filtered pulse
height (OFPH), in general has an unknown dependance on photon energy,
. Because the calibration function can only be measured at specific
points where photons of a known energy can be produced, this unknown dependence
of OFPH on leads to calibration errors and the need for
time-intensive calibration measurements and analysis. A calibration metric that
is nearly linear as a function of could help alleviate these
problems. In this work, we assess the linearity of a physically motivated
calibration metric, . We measure calibration pulses in the range 4.5
keV9.6 keV with detectors optimized for 6 keV photons to
compare the linearity properties of to OFPH. In these test data
sets, we find that fits a linear function an order of magnitude
better than OFPH. Furthermore, calibration functions using , an
optimized version of , are linear within the 2-3 eV noise of the
data
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