23,554 research outputs found
Pump-Enhanced Continuous-Wave Magnetometry using Nitrogen-Vacancy Ensembles
Ensembles of nitrogen-vacancy centers in diamond are a highly promising
platform for high-sensitivity magnetometry, whose efficacy is often based on
efficiently generating and monitoring magnetic-field dependent infrared
fluorescence. Here we report on an increased sensing efficiency with the use of
a 532-nm resonant confocal cavity and a microwave resonator antenna for
measuring the local magnetic noise density using the intrinsic nitrogen-vacancy
concentration of a chemical-vapor deposited single-crystal diamond. We measure
a near-shot-noise-limited magnetic noise floor of 200 pT/
spanning a bandwidth up to 159 Hz, and an extracted sensitivity of
approximately 3 nT/, with further enhancement limited by the
noise floor of the lock-in amplifier and the laser damage threshold of the
optical components. Exploration of the microwave and optical pump-rate
parameter space demonstrates a linewidth-narrowing regime reached by virtue of
using the optical cavity, allowing an enhanced sensitivity to be achieved,
despite an unoptimized collection efficiency of <2 %, and a low
nitrogen-vacancy concentration of about 0.2 ppb.Comment: 10 pages and 5 figure
Sensing-Throughput Tradeoff for Interweave Cognitive Radio System: A Deployment-Centric Viewpoint
Secondary access to the licensed spectrum is viable only if interference is
avoided at the primary system. In this regard, different paradigms have been
conceptualized in the existing literature. Of these, Interweave Systems (ISs)
that employ spectrum sensing have been widely investigated. Baseline models
investigated in the literature characterize the performance of IS in terms of a
sensing-throughput tradeoff, however, this characterization assumes the
knowledge of the involved channels at the secondary transmitter, which is
unavailable in practice. Motivated by this fact, we establish a novel approach
that incorporates channel estimation in the system model, and consequently
investigate the impact of imperfect channel estimation on the performance of
the IS. More particularly, the variation induced in the detection probability
affects the detector's performance at the secondary transmitter, which may
result in severe interference at the primary users. In this view, we propose to
employ average and outage constraints on the detection probability, in order to
capture the performance of the IS. Our analysis reveals that with an
appropriate choice of the estimation time determined by the proposed model, the
degradation in performance of the IS can be effectively controlled, and
subsequently the achievable secondary throughput can be significantly enhanced.Comment: 13 pages, 10 figures, Accepted to be published in IEEE Transactions
on Wireless Communication
Phase transitions in the condition number distribution of Gaussian random matrices
We study the statistics of the condition number
(the ratio between
largest and smallest squared singular values) of Gaussian random
matrices. Using a Coulomb fluid technique, we derive analytically and for large
the cumulative and tail-cumulative
distributions of . We find that these
distributions decay as and , where is the Dyson index of the ensemble. The left
and right rate functions are independent of and
calculated exactly for any choice of the rectangularity parameter
. Interestingly, they show a weak non-analytic behavior at
their minimum (corresponding to the average condition
number), a direct consequence of a phase transition in the associated Coulomb
fluid problem. Matching the behavior of the rate functions around
, we determine exactly the scale of typical fluctuations
and the tails of the limiting distribution of
. The analytical results are in excellent agreement with numerical
simulations.Comment: 5 pag. + 7 pag. Suppl. Material. 3 Figure
Towards More Precise Survey Photometry for PanSTARRS and LSST: Measuring Directly the Optical Transmission Spectrum of the Atmosphere
Motivated by the recognition that variation in the optical transmission of
the atmosphere is probably the main limitation to the precision of ground-based
CCD measurements of celestial fluxes, we review the physical processes that
attenuate the passage of light through the Earth's atmosphere. The next
generation of astronomical surveys, such as PanSTARRS and LSST, will greatly
benefit from dedicated apparatus to obtain atmospheric transmission data that
can be associated with each survey image. We review and compare various
approaches to this measurement problem, including photometry, spectroscopy, and
LIDAR. In conjunction with careful measurements of instrumental throughput,
atmospheric transmission measurements should allow next-generation imaging
surveys to produce photometry of unprecedented precision. Our primary concerns
are the real-time determination of aerosol scattering and absorption by water
along the line of sight, both of which can vary over the course of a night's
observations.Comment: 41 pages, 14 figures. Accepted PAS
Random Subsets of Structured Deterministic Frames have MANOVA Spectra
We draw a random subset of rows from a frame with rows (vectors) and
columns (dimensions), where and are proportional to . For a
variety of important deterministic equiangular tight frames (ETFs) and tight
non-ETF frames, we consider the distribution of singular values of the
-subset matrix. We observe that for large they can be precisely
described by a known probability distribution -- Wachter's MANOVA spectral
distribution, a phenomenon that was previously known only for two types of
random frames. In terms of convergence to this limit, the -subset matrix
from all these frames is shown to be empirically indistinguishable from the
classical MANOVA (Jacobi) random matrix ensemble. Thus empirically the MANOVA
ensemble offers a universal description of the spectra of randomly selected
-subframes, even those taken from deterministic frames. The same
universality phenomena is shown to hold for notable random frames as well. This
description enables exact calculations of properties of solutions for systems
of linear equations based on a random choice of frame vectors out of
possible vectors, and has a variety of implications for erasure coding,
compressed sensing, and sparse recovery. When the aspect ratio is small,
the MANOVA spectrum tends to the well known Marcenko-Pastur distribution of the
singular values of a Gaussian matrix, in agreement with previous work on highly
redundant frames. Our results are empirical, but they are exhaustive, precise
and fully reproducible
- …