291 research outputs found
Identifying capacitive and inductive loss in lumped element superconducting hybrid titanium nitride/aluminum resonators
We present a method to systematically locate and extract capacitive and
inductive losses in superconducting resonators at microwave frequencies by use
of mixed-material, lumped element devices. In these devices, ultra-low loss
titanium nitride was progressively replaced with aluminum in the
inter-digitated capacitor and meandered inductor elements. By measuring the
power dependent loss at 50 mK as the Al-TiN fraction in each element is
increased, we find that at low electric field, i.e. in the single photon limit,
the loss is two level system in nature and is correlated with the amount of Al
capacitance rather than the Al inductance. In the high electric field limit,
the remaining loss is linearly related to the product of the Al area times its
inductance and is likely due to quasiparticles generated by stray radiation. At
elevated temperature, additional loss is correlated with the amount of Al in
the inductance, with a power independent TiN-Al interface loss term that
exponentially decreases as the temperature is reduced. The TiN-Al interface
loss is vanishingly small at the 50 mK base temperature.Comment: 10 pages, 5 figure
Ownership and attitudes towards technology use in physiotherapy students from seven countries
PURPOSE: To assess differences in prerequisites to blended learning such as technology use and Internet access in an international sample of physiotherapy students from Bangladesh, Belgium, Brazil, Luxembourg, Sudan, Switzerland and South Africa.
RESULTS: Students' digital technology experiences were generally low. They primarily used a smartphone and a laptop to connect to the Internet. However, there was a significant difference between institutions in owning a laptop and access to Internet. Most students preferred learning in environments that included some online components but had never used Twitter or written a blog post and wanted less social media in their learning environments.
CONCLUSION: Physiotherapy students would prefer an increase in the use of digital tools in their learning. However, differences in technology use and access highlight the challenges inherent to offering international online courses. Therefore decisions around online and blended course design in health professions education must be made with caution.Michael Rowe receives funding from the South African National Research Foundation
Characterization and In-situ Monitoring of Sub-stoichiometric Adjustable Tc Titanium Nitride Growth
The structural and electrical properties of Ti-N films deposited by reactive
sputtering depend on their growth parameters, in particular the Ar:N2 gas
ratio. We show that the nitrogen percentage changes the crystallographic phase
of the film progressively from pure \alpha-Ti, through an \alpha-Ti phase with
interstitial nitrogen, to stoichiometric Ti2N, and through a substoichiometric
TiNX to stoichiometric TiN. These changes also affect the superconducting
transition temperature, Tc, allowing, the superconducting properties to be
tailored for specific applications. After decreasing from a Tc of 0.4 K for
pure Ti down to below 50 mK at the Ti2N point, the Tc then increases rapidly up
to nearly 5 K over a narrow range of nitrogen incorporation. This very sharp
increase of Tc makes it difficult to control the properties of the film from
wafer-to-wafer as well as across a given wafer to within acceptable margins for
device fabrication. Here we show that the nitrogen composition and hence the
superconductive properties are related to, and can be determined by,
spectroscopic ellipsometry. Therefore, this technique may be used for process
control and wafer screening prior to investing time in processing devices
Proximity-Coupled Ti/TiN Multilayers for use in Kinetic Inductance Detectors
We apply the superconducting proximity effect in TiN/Ti multi-layer films to
tune the critical temperature, Tc, to within 10 mK with high uniformity (less
than 15 mK spread) across a 75 mm wafer. Reproducible Tc's are obtained from
0.8 - 2.5 K. These films had high resistivities, > 100 uOhm-cm and internal
quality factors for resonators in the GHz range on the order of 100k and
higher. Both trilayers of TiN/Ti/TiN and thicker superlattice films were
prepared, demonstrating a highly controlled process for films over a wide
thickness range. Detectors were fabricated and showed single photon resolution
at 1550 nm. The high uniformity and controllability coupled with the high
quality factor, kinetic inductance, and inertness of TiN make these films ideal
for use in frequency multiplexed kinetic inductance detectors and other
potential applications such as nanowire detectors, transition edge sensors and
associated quantum information applications
Etch Induced Microwave Losses in Titanium Nitride Superconducting Resonators
We have investigated the correlation between the microwave loss and
patterning method for coplanar waveguide titanium nitride resonators fabricated
on Si wafers. Three different methods were investigated: fluorine- and
chlorine-based reactive ion etches and an argon-ion mill. At high microwave
probe powers the reactive etched resonators showed low internal loss, whereas
the ion-milled samples showed dramatically higher loss. At single-photon powers
we found that the fluorine-etched resonators exhibited substantially lower loss
than the chlorine-etched ones. We interpret the results by use of numerically
calculated filling factors and find that the silicon surface exhibits a higher
loss when chlorine-etched than when fluorine-etched. We also find from
microscopy that re-deposition of silicon onto the photoresist and side walls is
the probable cause for the high loss observed for the ion-milled resonator
Coherence in a transmon qubit with epitaxial tunnel junctions
We developed transmon qubits based on epitaxial tunnel junctions and
interdigitated capacitors. This multileveled qubit, patterned by use of
all-optical lithography, is a step towards scalable qubits with a high
integration density. The relaxation time T1 is .72-.86mu sec and the ensemble
dephasing time T2 is slightly larger than T1. The dephasing time T2 (1.36mu
sec) is nearly energy-relaxation-limited. Qubit spectroscopy yields weaker
level splitting than observed in qubits with amorphous barriers in
equivalent-size junctions. The qubit's inferred microwave loss closely matches
the weighted losses of the individual elements (junction, wiring dielectric,
and interdigitated capacitor), determined by independent resonator
measurements
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