7,537 research outputs found
NIKA: A millimeter-wave kinetic inductance camera
Current generation millimeter wavelength detectors suffer from scaling limits
imposed by complex cryogenic readout electronics. To circumvent this it is
imperative to investigate technologies that intrinsically incorporate strong
multiplexing. One possible solution is the kinetic inductance detector (KID).
In order to assess the potential of this nascent technology, a prototype
instrument optimized for the 2 mm atmospheric window was constructed. Known as
the N\'eel IRAM KIDs Array (NIKA), it was recently tested at the Institute for
Millimetric Radio Astronomy (IRAM) 30-meter telescope at Pico Veleta, Spain.
The measurement resulted in the imaging of a number of sources, including
planets, quasars, and galaxies. The images for Mars, radio star MWC349, quasar
3C345, and galaxy M87 are presented. From these results, the optical NEP was
calculated to be around WHz. A factor of 10
improvement is expected to be readily feasible by improvements in the detector
materials and reduction of performance-degrading spurious radiation.Comment: Accepted for publication in Astronomy & Astrophysic
YBCO microwave resonators for strong collective coupling with spin ensembles
Coplanar microwave resonators made of 330 nm-thick superconducting YBCO have
been realized and characterized in a wide temperature (, 2-100 K) and
magnetic field (, 0-7 T) range. The quality factor exceeds 10
below 55 K and it slightly decreases for increasing fields, remaining 90 of
for T and K. These features allow the coherent coupling
of resonant photons with a spin ensemble at finite temperature and magnetic
field. To demonstrate this, collective strong coupling was achieved by using
DPPH organic radical placed at the magnetic antinode of the fundamental mode:
the in-plane magnetic field is used to tune the spin frequency gap splitting
across the single-mode cavity resonance at 7.75 GHz, where clear anticrossings
are observed with a splitting as large as MHz at K. The
spin-cavity collective coupling rate is shown to scale as the square root of
the number of active spins in the ensemble.Comment: to appear in Appl. Phys. Let
NanoSQUID magnetometry of individual cobalt nanoparticles grown by focused electron beam induced deposition
We demonstrate the operation of low-noise nano superconducting quantum
interference devices (SQUIDs) based on the high critical field and high
critical temperature superconductor YBaCuO (YBCO) as
ultra-sensitive magnetometers for single magnetic nanoparticles (MNPs). The
nanoSQUIDs exploit the Josephson behavior of YBCO grain boundaries and have
been patterned by focused ion beam milling. This allows to precisely define the
lateral dimensions of the SQUIDs so as to achieve large magnetic coupling
between the nanoloop and individual MNPs. By means of focused electron beam
induced deposition, cobalt MNPs with typical size of several tens of nm have
been grown directly on the surface of the sensors with nanometric spatial
resolution. Remarkably, the nanoSQUIDs are operative over extremely broad
ranges of applied magnetic field (-1 T 1 T) and temperature (0.3
K 80 K). All these features together have allowed us to perform
magnetization measurements under different ambient conditions and to detect the
magnetization reversal of individual Co MNPs with magnetic moments (1 - 30)
. Depending on the dimensions and shape of the
particles we have distinguished between two different magnetic states yielding
different reversal mechanisms. The magnetization reversal is thermally
activated over an energy barrier, which has been quantified for the (quasi)
single-domain particles. Our measurements serve to show not only the high
sensitivity achievable with YBCO nanoSQUIDs, but also demonstrate that these
sensors are exceptional magnetometers for the investigation of the properties
of individual nanomagnets
Memristors for the Curious Outsiders
We present both an overview and a perspective of recent experimental advances
and proposed new approaches to performing computation using memristors. A
memristor is a 2-terminal passive component with a dynamic resistance depending
on an internal parameter. We provide an brief historical introduction, as well
as an overview over the physical mechanism that lead to memristive behavior.
This review is meant to guide nonpractitioners in the field of memristive
circuits and their connection to machine learning and neural computation.Comment: Perpective paper for MDPI Technologies; 43 page
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