2,787 research outputs found
Rapidly reconfigurable optically induced photonic crystals in hot rubidium vapor
Through periodic index modulation, we create two different types of photonic
structures in a heated rubidium vapor for controlled reflection, transmission
and diffraction of light. The modulation is achieved through the use of the AC
Stark effect resulting from a standing-wave control field. The periodic
intensity structures create translationally invariant index profiles analogous
to photonic crystals in spectral regions of steep dispersion. Experimental
results are consistent with modeling.Comment: 6 pages, 6 figure
Quantum Chaos, Delocalization, and Entanglement in Disordered Heisenberg Models
We investigate disordered one- and two-dimensional Heisenberg spin lattices
across a transition from integrability to quantum chaos from both a statistical
many-body and a quantum-information perspective. Special emphasis is devoted to
quantitatively exploring the interplay between eigenvector statistics,
delocalization, and entanglement in the presence of nontrivial symmetries. The
implications of basis dependence of state delocalization indicators (such as
the number of principal components) is addressed, and a measure of {\em
relative delocalization} is proposed in order to robustly characterize the
onset of chaos in the presence of disorder. Both standard multipartite and {\em
generalized entanglement} are investigated in a wide parameter regime by using
a family of spin- and fermion- purity measures, their dependence on
delocalization and on energy spectrum statistics being examined. A distinctive
{\em correlation between entanglement, delocalization, and integrability} is
uncovered, which may be generic to systems described by the two-body random
ensemble and may point to a new diagnostic tool for quantum chaos. Analytical
estimates for typical entanglement of random pure states restricted to a proper
subspace of the full Hilbert space are also established and compared with
random matrix theory predictions.Comment: 17 pages, 10 figures, revised versio
Precision frequency measurements with interferometric weak values
We demonstrate an experiment which utilizes a Sagnac interferometer to
measure a change in optical frequency of 129 kHz per root Hz with only 2 mW of
continuous wave, single mode input power. We describe the measurement of a weak
value and show how even higher frequency sensitivities may be obtained over a
bandwidth of several nanometers. This technique has many possible applications,
such as precision relative frequency measurements and laser locking without the
use of atomic lines.Comment: 4 pages, 3 figures, published in PR
Ultrasensitive Beam Deflection Measurement via Interferometric Weak Value Amplification
We report on the use of an interferometric weak value technique to amplify
very small transverse deflections of an optical beam. By entangling the beam's
transverse degrees of freedom with the which-path states of a Sagnac
interferometer, it is possible to realize an optical amplifier for polarization
independent deflections. The theory for the interferometric weak value
amplification method is presented along with the experimental results, which
are in good agreement. Of particular interest, we measured the angular
deflection of a mirror down to 560 femtoradians and the linear travel of a
piezo actuator down to 20 femtometers
Optimizing the Signal to Noise Ratio of a Beam Deflection Measurement with Interferometric Weak Values
The amplification obtained using weak values is quantified through a detailed
investigation of the signal to noise ratio for an optical beam deflection
measurement. We show that for a given deflection, input power and beam radius,
the use of interferometric weak values allows one to obtain the optimum signal
to noise ratio using a coherent beam. This method has the advantage of reduced
technical noise and allows for the use of detectors with a low saturation
intensity. We report on an experiment which improves the signal to noise ratio
for a beam deflection measurement by a factor of 54 when compared to a
measurement using the same beam size and a quantum limited detector
Continuous phase amplification with a Sagnac interferometer
We describe a weak value inspired phase amplification technique in a Sagnac
interferometer. We monitor the relative phase between two paths of a slightly
misaligned interferometer by measuring the average position of a split-Gaussian
mode in the dark port. Although we monitor only the dark port, we show that the
signal varies linearly with phase and that we can obtain similar sensitivity to
balanced homodyne detection. We derive the source of the amplification both
with classical wave optics and as an inverse weak value.Comment: 5 pages, 4 figures, previously submitted for publicatio
Extracting an Entanglement Signature from Only Classical Mutual Information
We introduce a quantity which is formed using classical notions of mutual information and which is computed using the results of projective measurements. This quantity constitutes a sufficient condition for entanglement and represents the amount of information that can be extracted from a bipartite system for spacelike separated observers. In addition to discussion, we provide simulations as well as experimental results for the singlet and maximally correlated mixed states
Interferometric weak value deflections: quantum and classical treatments
We derive the weak value deflection given in a paper by Dixon et al. (Phys.
Rev. Lett. 102, 173601 (2009)) both quantum mechanically and classically. This
paper is meant to cover some of the mathematical details omitted in that paper
owing to space constraints
All Optical Waveguiding in a Coherent Atomic Rubidium Vapor
We demonstrate an all optical waveguide imprinted by a low power Laguerre Gaussian control laser beam using a coherent Raman process in warm atomic rubidium vapor. We show that the signal beam propagates with a small spot size over several diffraction lengths. We also show that the coupling efficiency of the signal beam into the waveguide varies linearly with the signal power
The hidden X-ray breaks in afterglow light curves
Gamma-Ray Burst (GRB) afterglow observations in the Swift era have a
perceived lack of achromatic jet breaks compared to the BeppoSAX, or pre-Swift
era. Specifically, relatively few breaks, consistent with jet breaks, are
observed in the X-ray light curves of these bursts. If these breaks are truly
missing, it has serious consequences for the interpretation of GRB jet
collimation and energy requirements, and the use of GRBs as standard candles.
Here we address the issue of X-ray breaks which are possibly 'hidden' and
hence the light curves are misinterpreted as being single power-laws. We show
how a number of precedents, including GRB 990510 & GRB 060206, exist for such
hidden breaks and how, even with the well sampled light curves of the Swift
era, these breaks may be left misidentified. We do so by synthesising X-ray
light curves and finding general trends via Monte Carlo analysis. Furthermore,
in light of these simulations, we discuss how to best identify achromatic
breaks in afterglow light curves via multi-wavelength analysis.Comment: 4 pages, contributed talk, submitted to the proceedings of Gamma Ray
Bursts 2007, Santa Fe, New Mexico, November 5-9 200
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