6,721 research outputs found
Robust Near-Field 3D Localization of an Unaligned Single-Coil Agent Using Unobtrusive Anchors
The magnetic near-field provides a suitable means for indoor localization,
due to its insensitivity to the environment and strong spatial gradients. We
consider indoor localization setups consisting of flat coils, allowing for
convenient integration of the agent coil into a mobile device (e.g., a smart
phone or wristband) and flush mounting of the anchor coils to walls. In order
to study such setups systematically, we first express the Cram\'er-Rao lower
bound (CRLB) on the position error for unknown orientation and evaluate its
distribution within a square room of variable size, using 15 x 10cm anchor
coils and a commercial NFC antenna at the agent. Thereby, we find cm-accuracy
being achievable in a room of 10 x 10 x 3 meters with 12 flat wall-mounted
anchors and with 10mW used for the generation of magnetic fields. Practically
achieving such estimation performance is, however, difficult because of the
non-convex 5D likelihood function. To that end, we propose a fast and accurate
weighted least squares (WLS) algorithm which is insensitive to initialization.
This is enabled by effectively eliminating the orientation nuisance parameter
in a rigorous fashion and scaling the individual anchor observations, leading
to a smoothed 3D cost function. Using WLS estimates to initialize a
maximum-likelihood (ML) solver yields accuracy near the theoretical limit in up
to 98% of cases, thus enabling robust indoor localization with unobtrusive
infrastructure, with a computational efficiency suitable for real-time
processing.Comment: 7 pages, to be presented at IEEE PIMRC 201
High Kinetic Inductance Superconducting Nanowire Resonators for Circuit QED in a Magnetic Field
We present superconducting microwave-frequency resonators based on NbTiN
nanowires. The small cross section of the nanowires minimizes vortex
generation, making the resonators resilient to magnetic fields. Measured
intrinsic quality factors exceed in a T in-plane magnetic
field, and in a mT perpendicular magnetic field. Due to
their high characteristic impedance, these resonators are expected to develop
zero-point voltage fluctuations one order of magnitude larger than in standard
coplanar waveguide resonators. These properties make the nanowire resonators
well suited for circuit QED experiments needing strong coupling to quantum
systems with small electric dipole moments and requiring a magnetic field, such
as electrons in single and double quantum dots
Dynamical decoherence of the light induced interlayer coupling in YBaCuO
Optical excitation of apical oxygen vibrations in
YBaCuO has been shown to enhance its c-axis
superconducting-phase rigidity, as evidenced by a transient blue shift of the
equilibrium inter-bilayer Josephson plasma resonance. Surprisingly, a transient
c-axis plasma mode could also be induced above T by the same apical
oxygen excitation, suggesting light activated superfluid tunneling throughout
the pseudogap phase of YBaCuO. However, despite the
similarities between the above T transient plasma mode and the
equilibrium Josephson plasmon, alternative explanations involving high mobility
quasiparticle transport should be considered. Here, we report an extensive
study of the relaxation of the light-induced plasmon into the equilibrium
incoherent phase. These new experiments allow for a critical assessment of the
nature of this mode. We determine that the transient plasma relaxes through a
collapse of its coherence length rather than its carrier (or superfluid)
density. These observations are not easily reconciled with quasiparticle
interlayer transport, and rather support transient superfluid tunneling as the
origin of the light-induced interlayer coupling in
YBaCuO.Comment: 27 pages (17 pages main text, 10 pages supplementary), 5 figures
(main text
Tunable negative permeability in a three-dimensional superconducting metamaterial
We report on highly tunable radio frequency (rf) characteristics of a
low-loss and compact three dimensional (3D) metamaterial made of
superconducting thin film spiral resonators. The rf transmission spectrum of a
single element of the metamaterial shows a fundamental resonance peak at
24.95 MHz that shifts to a 25 smaller frequency and becomes
degenerate when a 3D array of such elements is created. The metamaterial shows
an \emph{in-situ} tunable narrow frequency band in which the real part of the
effective permeability is negative over a wide range of temperature, which
reverts to gradually near-zero and positive values as the superconducting
critical temperature is approached. This metamaterial can be used for
increasing power transfer efficiency and tunability of electrically small
rf-antennas.Comment: 6 pages, 4 figure
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