161 research outputs found
Kinetic Inductance Magnetometer
Ultrasensitive magnetic field detection is utilized in the fields of science,
medicine and industry. We report on a novel magnetometer relying on the kinetic
inductance of superconducting material. The kinetic inductance exhibits a
non-linear response with respect to DC current, a fact that is exploited by
applying magnetic flux through a superconducting loop to generate a shielding
current and a change in the inductance of the loop. The magnetometer is
arranged into a resonator, allowing readout through a transmission measurement
that makes the device compatible with radio frequency multiplexing techniques.
The device is fabricated using a single thin-film layer of NbN, simplifying the
fabrication process compared to existing magnetometer technologies
considerably. Our experimental data, supported by theory, demonstrates a
magnetometer having potential to replace established technology in applications
requiring ultra-high sensitivity.Comment: 16 pages, 6 figure
Flux-driven Josephson parametric amplifier for sub-GHz frequencies fabricated with side-wall passivated spacer junction technology
We present experimental results on a Josephson parametric amplifier tailored
for readout of ultra-sensitive thermal microwave detectors. In particular, we
discuss the impact of fabrication details on the performance. We show that the
small volume of deposited dielectric materials enabled by the side-wall
passivated spacer niobium junction technology leads to robust operation across
a wide range of operating temperatures up to 1.5 K. The flux-pumped amplifier
has gain in excess of 20 dB in three-wave mixing and its center frequency is
tunable between 540 MHz and 640 MHz. At 600 MHz, the amplifier adds 105 mK
9 mK of noise, as determined with the hot/cold source method.
Phase-sensitive amplification is demonstrated with the device
Multiplexed readout of kinetic inductance bolometer arrays
Kinetic inductance bolometer (KIB) technology is a candidate for passive
sub-millimeter wave and terahertz imaging systems. Its benefits include
scalability into large 2D arrays and operation with intermediate cryogenics in
the temperature range of 5 -- 10 K. We have previously demonstrated the
scalability in terms of device fabrication, optics integration, and cryogenics.
In this article, we address the last missing ingredient, the readout. The
concept, serial addressed frequency excitation (SAFE), is an alternative to
full frequency-division multiplexing at microwave frequencies conventionally
used to read out kinetic inductance detectors. We introduce the concept, and
analyze the criteria of the multiplexed readout avoiding the degradation of the
signal-to-noise ratio in the presence of a thermal anti-alias filter inherent
to thermal detectors. We present a practical scalable realization of a readout
system integrated into a prototype imager with 8712 detectors. This is used for
demonstrating the noise properties of the readout. Furthermore, we present
practical detection experiments with a stand-off laboratory-scale imager.Comment: 7 pages, 6 figure
Characterizing cryogenic amplifiers with a matched temperature-variable noise source
We present a cryogenic microwave noise source with a characteristic impedance
of 50 , which can be installed in a coaxial line of a cryostat. The
bath temperature of the noise source is continuously variable between 0.1 K and
5 K without causing significant back-action heating on the sample space. As a
proof-of-concept experiment, we perform Y-factor measurements of an amplifier
cascade that includes a traveling wave parametric amplifier and a commercial
high electron mobility transistor amplifier. We observe system noise
temperatures as low as mK at 5.7 GHz corresponding to
excess photons. The system we present has immediate
applications in the validation of solid-state qubit readout lines.Comment: The following article has been accepted by Review of Scientific
Instruments. After it is published, it will be found at
https://doi.org/10.1063/5.002895
Conformal Titanium Nitride in a Porous Silicon Matrix: a Nanomaterial for In-Chip Supercapacitors
Today's supercapacitor energy storages are typically discrete devices aimed
for printed boards and power applications. The development of autonomous sensor
networks and wearable electronics and the miniaturisation of mobile devices
would benefit substantially from solutions in which the energy storage is
integrated with the active device. Nanostructures based on porous silicon (PS)
provide a route towards integration due to the very high inherent surface area
to volume ratio and compatibility with microelectronics fabrication processes.
Unfortunately, pristine PS has limited wettability and poor chemical stability
in electrolytes and the high resistance of the PS matrix severely limits the
power efficiency. In this work, we demonstrate that excellent wettability and
electro-chemical properties in aqueous and organic electrolytes can be obtained
by coating the PS matrix with an ultra-thin layer of titanium nitride by atomic
layer deposition. Our approach leads to very high specific capacitance (15
F/cm), energy density (1.3 mWh/cm), power density (up to 214 W/cm)
and excellent stability (more than 13,000 cycles). Furthermore, we show that
the PS-TiN nanomaterial can be integrated inside a silicon chip monolithically
by combining MEMS and nanofabrication techniques. This leads to realisation of
in-chip supercapacitor, i.e., it opens a new way to exploit the otherwise
inactive volume of a silicon chip to store energy
Signal crosstalk in a flip-chip quantum processor
Quantum processors require a signal-delivery architecture with high
addressability (low crosstalk) to ensure high performance already at the scale
of dozens of qubits. Signal crosstalk causes inadvertent driving of quantum
gates, which will adversely affect quantum-gate fidelities in scaled-up
devices. Here, we demonstrate packaged flip-chip superconducting quantum
processors with signal-crosstalk performance competitive with those reported in
other platforms. For capacitively coupled qubit-drive lines, we find
on-resonant crosstalk better than -27 dB (average -37 dB). For inductively
coupled magnetic-flux-drive lines, we find less than 0.13 % direct-current flux
crosstalk (average 0.05 %). These observed crosstalk levels are adequately
small and indicate a decreasing trend with increasing distance, which is
promising for further scaling up to larger numbers of qubits. We discuss the
implication of our results for the design of a low-crosstalk, on-chip signal
delivery architecture, including the influence of a shielding tunnel structure,
potential sources of crosstalk, and estimation of crosstalk-induced qubit-gate
error in scaled-up quantum processors.Comment: 16 pages, 12 figures, includes appendice
Characterization of a fabrication process for the integration of superconducting qubits and RSFQ circuits
In order to integrate superconducting qubits with rapid-single-flux-quantum
(RSFQ) control circuitry, it is necessary to develop a fabrication process that
fulfills at the same time the requirements of both elements: low critical
current density, very low operating temperature (tens of milliKelvin) and
reduced dissipation on the qubit side; high operation frequency, large
stability margins, low dissipated power on the RSFQ side. For this purpose, VTT
has developed a fabrication process based on Nb trilayer technology, which
allows the on-chip integration of superconducting qubits and RSFQ circuits even
at very low temperature. Here we present the characterization (at 4.2 K) of the
process from the point of view of the Josephson devices and show that they are
suitable to build integrated superconducting qubits
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