62 research outputs found
Analytical model of the readout power and SQUID hysteresis parameter dependence of the resonator characteristics of microwave SQUID multiplexers
We report on the development of an analytical model describing the readout
power and SQUID hysteresis parameter dependence of the resonator
characteristics used for frequency encoding in microwave SQUID multiplexers.
Within the context of this model, we derived the different dependencies by
analyzing the Fourier components of the non-linear response of the
non-hysteretic rf-SQUID. We show that our model contains the existing model as
a limiting case, leading to identical analytical expressions for small readout
powers. Considering the approximations we made, our model is valid for rf-SQUID
hysteresis parameters which fully covers the
parameter range of existing multiplexer devices. We conclude our work with an
experimental verification of the model. In particular, we demonstrate a very
good agreement between measured multiplexer characteristics and predictions
based on our model.Comment: This article has been submitted to Superconductor Science and
Technolog
Magnetic microcalorimeter with paramagnetic temperature sensors and integrated dc-SQUID readout for high-resolution X-ray emission spectroscopy
We present two variants of a magnetic microcalorimeter with paramagnetic
temperature sensors and integrated dc-SQUID readout for high-resolution X-ray
emission spectroscopy. Each variant employs two overhanging gold absorbers with
a sensitive area of 150m x 150m and a thickness of 3m, thus
providing a quantum efficiency of 98% for photons up to 5keV and 50% for
photons up to 10keV. The first variant turned out to be fully operational, but,
at the same time, to suffer from Joule power dissipation of the Josephson
junction shunt resistors, athermal phonon loss, and slew rate limitations of
the overall setup. Overall, it only achieved an energy resolution . In the second variant, we introduced an innovative
`tetrapod absorber geometry' as well as a membrane-technique for protecting the
temperature sensors against the power dissipation of the shunt resistors. By
this, the second variant achieves an outstanding energy resolution of and hence provides, to our knowledge, the present
best energy resolving power among all existing
energy-dispersive detectors for soft and tender X-rays.Comment: submitted to Applied Physics Letter
Development and characterisation of high-resolution microcalorimeter detectors for the ECHo-100k experiment
The goal of the ECHo experiment is a direct determination of the absolute
scale of the neutrino mass by the analysis of the end-point region of the
Ho-163 electron capture (EC) spectrum. The results of the first phase of the
experiment, ECHo-1k, have paved the way for the current phase, ECHo-100k, which
aims at a sensitivity below 2 eV on the effective electron neutrino mass. In
order to reach this goal, a new generation of high-resolution magnetic
microcalorimeters with embedded Ho-163 have been developed and characterised.
The design has been optimised to meet all the challenging requirements of the
ECHo-100k experimental phase, such as excellent energy resolution, wafer scale
implantation and multi-chip operation with multiplexing read-out. We present
the optimisation studies, the final design of the detector array and the first
characterisation studies. The results demonstrate that the detectors fully
match and even surpass the requirements for the current experimental phase,
ECHo-100k
Measuring Magnetic 1/f Noise in Superconducting Microstructures and the Fluctuation-Dissipation Theorem
The performance of superconducting devices like qubits, SQUIDs, and particle
detectors is often limited by finite coherence times and 1/f noise. Various
types of slow fluctuators in the Josephson junctions and the passive parts of
these superconducting circuits can be the cause, and devices usually suffer
from a combination of different noise sources, which are hard to disentangle
and therefore hard to eliminate. One contribution is magnetic 1/f noise caused
by fluctuating magnetic moments of magnetic impurities or dangling bonds in
superconducting inductances, surface oxides, insulating oxide layers, and
adsorbates. In an effort to further analyze such sources of noise, we have
developed an experimental set-up to measure both the complex impedance of
superconducting microstructures, and the overall noise picked up by these
structures. This allows for important sanity checks by connecting both
quantities via the fluctuation-dissipation theorem. Since these two
measurements are sensitive to different types of noise, we are able to identify
and quantify individual noise sources. The superconducting inductances under
investigation form a Wheatstone-like bridge, read out by two independent
cross-correlated dc-SQUID read-out chains. The resulting noise resolution lies
beneath the quantum limit of the front-end SQUIDs and lets us measure noise
caused by just a few ppm of impurities in close-by materials. We present
measurements of the insulating SiO2 layers of our devices, and magnetically
doped noble metal layers in the vicinity of the pickup coils at T = 30 mK - 800
mK and f = 1 Hz - 100 kHz.Comment: 13 pages, 5 figure
Flux ramp modulation based MHz frequency-division dc-SQUID multiplexer
We present a MHz frequency-division dc-SQUID multiplexer that is based on
flux ramp modulation and a series array of identical current-sensing
dc-SQUIDs with tightly coupled input coil. By running a periodic,
sawtooth-shaped current signal through an additional modulation coil being
tightly, but non-uniformly coupled to the individual SQUIDs, the voltage drop
across the array changes according to the superposition of the flux-to-voltage
characteristics of the individual SQUIDs within each cycle of the modulation
signal. In this mode of operation, an input signal injected in the input coil
of one of the SQUIDs and being quasi-static within a time frame adds a constant
flux offset and leads to a phase shift of the associated SQUID characteristics.
The latter is inherently proportional to the input signal and can be inferred
by channelizing and down-converting the sampled array output voltage. Using a
prototype multiplexer as well as a self-developed high-speed readout
electronics for real-time phase determination, we demonstrate the simultaneous
readout of four signal sources with MHz bandwidth per channel.Comment: The article has been submitted to Applied Physics Letter
Simultaneous MMC readout using a tailored {\mu}MUX based readout system
Magnetic microcalorimeters (MMCs) are cryogenic, energy-dispersive
single-particle detectors providing excellent energy resolution, intrinsically
fast signal rise time, quantum efficiency close to 100\%, large dynamic range
as well as almost ideal linear response. One of the remaining challenges to be
overcome to ultimately allow for the utilization of large-scale MMC based
detector arrays with thousands to millions of individual pixels is the
realization of a SQUID based multiplexing technique particularly tailored for
MMC readout. Within this context, we report on the first truly multiplexed
readout of an MMC based detector array using a frequency-division multiplexing
approach realized by a custom microwave SQUID multiplexer based readout system.Comment: Conference: ASC2022 (accepted for publication in IEEE Transactions on
Applied Superconductivity
DELight: a Direct search Experiment for Light dark matter with superfluid helium
To reach ultra-low detection thresholds necessary to probe unprecedentedly
low Dark Matter masses, target material alternatives and novel detector designs
are essential. One such target material is superfluid He which has the
potential to probe so far uncharted light Dark Matter parameter space at
sub-GeV masses. The new ``Direct search Experiment for Light dark matter'',
DELight, will be using superfluid helium as active target, instrumented with
magnetic micro-calorimeters. It is being designed to reach sensitivity to
masses well below 100\,MeV in Dark Matter-nucleus scattering interactions.Comment: IDM2022 proceedings submitted to SciPos
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