108 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
Differential Bloch Oscillating Transistor Pair
We examine a Bloch Oscillating Transistor pair as a differential stage for
cryogenic low-noise measurements. Using two oppositely biased, nearly symmetric
Bloch Oscillating Transistors, we measured the sum and difference signals in
the current gain and transconductance modes while changing the common mode
signal, either voltage or current. From the common mode rejection ratio we find
values dB even under non-optimal conditions. We also characterize the
noise properties and obtain excellent noise performance for measurements having
source impedances in the M range.Comment: 8 pages, 3 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
Advanced Concepts in Josephson Junction Reflection Amplifiers
Low-noise amplification atmicrowave frequencies has become increasingly
important for the research related to superconducting qubits and
nanoelectromechanical systems. The fundamental limit of added noise by a
phase-preserving amplifier is the standard quantum limit, often expressed as
noise temperature . Towards the goal of the
quantum limit, we have developed an amplifier based on intrinsic negative
resistance of a selectively damped Josephson junction. Here we present
measurement results on previously proposed wide-band microwave amplification
and discuss the challenges for improvements on the existing designs. We have
also studied flux-pumped metamaterial-based parametric amplifiers, whose
operating frequency can be widely tuned by external DC-flux, and demonstrate
operation at pumping, in contrast to the typical metamaterial
amplifiers pumped via signal lines at .Comment: 9 pages, 6 figure
Dynamics of Bloch oscillating transistor near the bifurcation threshold
The tendency to bifurcate can often be utilized to improve performance characteristics of amplifiers or even to build detectors. The Bloch oscillating transistor is such a device. Here, we show that bistable behavior can be approached by tuning the base current and that the critical value depends on the Josephson coupling energy EJ of the device. We demonstrate current-gain enhancement for the device operating near the bifurcation point at small EJ. From our results for the current gains at various EJ, we determine the bifurcation threshold on the EJ-base current plane. The bifurcation threshold curve can be understood using the interplay of interband and intraband tunneling events.Peer reviewe
Thermoelectric bolometers based on ultra-thin heavily doped single-crystal silicon membranes
We present ultra-thin silicon membrane thermocouple bolometers suitable for
fast and sensitive detection of low levels of thermal power and infrared
radiation at room temperature. The devices are based on 40 nm-thick strain
tuned single crystalline silicon membranes shaped into heater/absorber area and
narrow n- and p-doped beams, which operate as the thermocouple. The
electro-thermal characterization of the devices reveal noise equivalent power
of 13 pW/rtHz and thermal time constant of 2.5 ms. The high sensitivity of the
devices is due to the high Seebeck coefficient of 0.39 mV/K and reduction of
thermal conductivity of the Si beams from the bulk value. The bolometers
operate in the Johnson-Nyquist noise limit of the thermocouple, and the
performance improvement towards the operation close to the temperature
fluctuation limit is discussed.Comment: 11 pages, 3 figure
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
Dynamical Casimir effect in a Josephson metamaterial
Vacuum modes confined into an electromagnetic cavity give rise to an
attractive interaction between the opposite walls. When the distance between
the walls is changed non-adiabatically, virtual vacuum modes are turned into
real particles, i.e. photons are generated out of the vacuum. These effects are
known as the static and dynamical Casimir effect, respectively. Here we
demonstrate the dynamical Casimir effect using a Josephson metamaterial
embedded in a microwave cavity at 5.4 GHz. We achieve the non-adiabatic change
in the effective length of the cavity by flux-modulation of the SQUID-based
metamaterial, which results in a few percent variation in the velocity of
light. We show that energy-correlated photons are generated from the ground
state of the cavity and that their power spectra display a bimodal frequency
distribution. These results are in excellent agreement with theoretical
predictions, all the way to the regime where classical parametric effects
cannot be of consequence.Comment: 4 pages, 3 figures, supplement at http://ltl.tkk.fi/~pjh/DCE
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