7,107 research outputs found
Two-dimensional exciton-polariton interactions beyond the Born approximation
We provide a many-body theory for the interactions of two-dimensional
excitons and polaritons beyond the Born approximation. Taking into account
Gaussian quantum fluctuations via the Bogoliubov theory, we find that the
two-body interaction strength in two-dimensions has an inverse logarithmic
dependence on the scattering length and ground state energy. This leads to a
vanishing exciton interaction strength in the zero-momentum limit but a finite
polariton interaction strength due to strong light-matter coupling. We also
derive the exact Tan relations for exciton-polaritons and calculate Tan's
contact coefficient. We show the polariton interaction strength and Tan's
contact both exhibit an anomalous enhancement at red photon-exciton detuning
when the scattering length is large. Our predictions may provide a
qualitatively correct guide for studies of exciton and polariton
nonlinearities, and suggest a route to achieving strongly nonlinear polariton
gases.Comment: 6 pages, 3 figures + 8 pages of Supplemental Material; many-body
calculations (Bogoliubov theory) using a bosonic model Hamiltonia
A Compact Orbital Angular Momentum Spectrometer Using Quantum Zeno Interrogation
We present a scheme to measure the orbital angular momentum spectrum of light
using a precisely timed optical loop and quantum non-demolition measurements.
We also discuss the influence of imperfect optical components.Comment: 8 pages, 6 figure
Beyond Gaussian Approximation: Bootstrap for Maxima of Sums of Independent Random Vectors
The Bonferroni adjustment, or the union bound, is commonly used to study rate
optimality properties of statistical methods in high-dimensional problems.
However, in practice, the Bonferroni adjustment is overly conservative. The
extreme value theory has been proven to provide more accurate multiplicity
adjustments in a number of settings, but only on ad hoc basis. Recently,
Gaussian approximation has been used to justify bootstrap adjustments in large
scale simultaneous inference in some general settings when ,
where is the multiplicity of the inference problem and is the sample
size. The thrust of this theory is the validity of the Gaussian approximation
for maxima of sums of independent random vectors in high-dimension. In this
paper, we reduce the sample size requirement to for the
consistency of the empirical bootstrap and the multiplier/wild bootstrap in the
Kolmogorov-Smirnov distance, possibly in the regime where the Gaussian
approximation is not available. New comparison and anti-concentration theorems,
which are of considerable interest in and of themselves, are developed as
existing ones interweaved with Gaussian approximation are no longer applicable
Theory of Ideal Four-Wave Mixing in Bose-Einstein Condensates
Starting from a second-quantized Hamiltonian of many-particle systems, we
derive the Gross-Pitaevskii (GP) equation in momentum space, which is suitable
for studying the multi-wave mixing processes of coherent matter waves. The
coupling equations are then applied to study ideal four-wave mixing (4WM), in
which only four waves with definite wavevectors are involved. Some interesting
problems of 4WM, such as the phase-matching condition, the collapse and revival
behaviour, the effects of relative phase difference, and the conversion
efficiency are discussed in detail. We also show that the main characters of
recent 4WM experiment [Deng et al, Nature 398, 218 (1999)] can be undersood in
the present simplified model.Comment: 5 Pages and 4 EPS figure
What is the best planar cavity for maximizing coherent exciton-photon coupling
We compare alternative planar cavity structures for strong excitonphoton
coupling, where the conventional distributed Bragg reflector (DBR) and three
unconventional types of cavity mirrors air/GaAs DBR, Tamm plasmon mirror
and subwavelength grating mirror. We design and optimize the planar cavities
built with each type of mirror at one side or both sides for maximum vacuum
field strength. We discuss the tradeoff between performance and fabrication
difficulty for each cavity structure. We show that cavities with
subwavelength grating mirrors allow simultaneously strongest field and high
cavity quality. The optimization principles and techniques developed in this
work will guide the cavity design for research and applications of
matterlight coupled semiconductors, especially new material systems that
require greater flexibility in the choice of cavity materials and cavity
fabrication procedures
On Midrange Periodicities in Solar Radio Flux and Sunspot Areas
Using the Hilbert-Huang transform technique, we investigate the midrange
periodicities in solar radio flux at 2800 MHz (F10.7) and sunspot areas (SAs)
from February 1, 1947 to September 30, 2016. The following prominent results
are found: (1) The quasi-periodic oscillations of both data sets are not
identical, such as the rotational cycle, the midrange periodicities, and the
Schwabe cycle. In particular, the midrange periodicities ranging from 37.9 days
to 297.3 days are related to the magnetic Rossby-type waves; 2) The 1.3-year
and 1.7-year fluctuations in solar activity indicators are surface
manifestations (from photosphere to corona) of magnetic flux changes generated
deep inside the Sun; 3) At the timescale of the Schwabe cycle, \textbf{the
complicated phase relationships} in the three intervals (1947-1958, 1959-1988,
and 1989-2016) agree with the produced periodicities of the magnetic
Rossby-type waves. \textbf{The findings indicate that the magnetic Rossby-type
waves are the possible physical mechanism behind the midrange periodicities of
solar activity indicators. Moreover, the significant change in the relationship
between photospheric and coronal activity took place after the maximum of solar
cycle 22 could be interpreted by the magnetic Rossby-type waves
Spectrum and electromagnetic transitions of bottomonium
Stimulated by the exciting progress in the observation of new bottomonium
states, we study the bottomonium spectrum. To calculate the mass spectrum, we
adopt a nonrelativistic screened potential model. The radial Schr\"{o}dinger
equation is solved with the three-point difference central method, where the
spin-dependent potentials are dealt with non-perturbatively. With this
treatment, the corrections of the spin-dependent potentials to the wave
functions can be included successfully. Furthermore, we calculate the
electromagnetic transitions of the (), (), and
() bottomonium states with a nonrelativistic electromagnetic
transition operator widely applied to meson photoproduction reactions. Our
predicted masses, hyperfine and fine splittings, electromagnetic transition
widths and branching ratios of the bottomonium states are in good agreement
with the available experimental data. Especially, the EM transitions of
, which were not well understood in
previous studies, can be reasonably explained by considering the corrections of
the spin-dependent interactions to the wave functions. We also discuss the
observations of the missing bottomonium states by using radiative transitions.
Some important radiative decay chains involving the missing bottomonium states
are suggested to be observed. We hope our study can provide some useful
references to observe and measure the properties of bottomonium mesons in
forthcoming experiments.Comment: 14 pages, 1 figure, revised version. To appear in PR
A Subpixel Registration Algorithm for Low PSNR Images
This paper presents a fast algorithm for obtaining high-accuracy subpixel
translation of low PSNR images. Instead of locating the maximum point on the
upsampled images or fitting the peak of correlation surface, the proposed
algorithm is based on the measurement of centroid on the cross correlation
surface by Modified Moment method. Synthetic images, real solar images and
standard testing images with white Gaussian noise added were tested, and the
results show that the accuracies of our algorithm are comparable with other
subpixel registration techniques and the processing speed is higher. The
drawback is also discussed at the end of this paper.Comment: in 2012 IEEE 5th Int. Conf. on Advanced Computational Intelligence
(ICACI) (New York: IEEE), 62
Improving Anti-Eavesdropping Ability without Eavesdropper's CSI: A Practical Secure Transmission Design Perspective
This letter studies the practical design of secure transmissions without
knowing eavesdropper's channel state information (ECSI). An ECSI-irrelevant
metric is introduced to quantize the intrinsic anti-eavesdropping ability (AEA)
that the transmitter has on confronting the eavesdropper via secrecy encoding
together with artificial-noise-aided signaling. Non-adaptive and adaptive
transmission schemes are proposed to maximize the AEA with the optimal encoding
rates and power allocation presented in closed-form expressions. Analyses and
numerical results show that maximizing the AEA is equivalent to minimizing the
secrecy outage probability (SOP) for the worst case by ignoring eavesdropper's
receiver noise. Therefore, the AEA is a useful alternative to the SOP for
assessing and designing secure transmissions when the ECSI cannot be prior
known.Comment: 4 pages, 2 figures, to be published on IEEE Wireless Communications
Letters (WCL
High Fidelity Detection of the Orbital Angular Momentum of Light by Time Mapping
We demonstrate high-fidelity detection of the orbital angular momentum (OAM)
of light using a compact and practical OAM spectrometer that maps the OAM
spectrum to time. The spectrometer consists of a single optical delay loop to
achieve timing mapping, a vortex phase plate that iteratively decreases the OAM
value, and a single mode fibre to distinguish zero from non-zero OAM states.
Light with arbitrarily OAM compositions can be measured. For light with OAM up
to 4hbar, we measured an average crosstalk of -21.3 dB, which is mainly limited
by the purity of the input states and optical alignment.Comment: 14 pages, 5 figure
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