16,250 research outputs found
Phase Space Tomography of Classical and Nonclassical Vibrational States of Atoms in an Optical Lattice
Atoms trapped in optical lattice have long been a system of interest in the
AMO community, and in recent years much study has been devoted to both short-
and long-range coherence in this system, as well as to its possible
applications to quantum information processing. Here we demonstrate for the
first time complete determination of the quantum phase space distributions for
an ensemble of atoms in such a lattice, including a negative Wigner
function for atoms in an inverted state.Comment: Submitted to Journal of Optics B: Quantum and Semiclassical Optics.
Special issue in connection with the 9th International Conference on Squeezed
States and Uncertainty Relations, to be held in Besancon, France, on 2-6 May
200
Nonlinear optics with less than one photon
We demonstrate suppression and enhancement of spontaneous parametric down-
conversion via quantum interference with two weak fields from a local
oscillator (LO). Pairs of LO photons are observed to upconvert with high
efficiency for appropriate phase settings, exhibiting an effective nonlinearity
enhanced by at least 10 orders of magnitude. This constitutes a two-photon
switch, and promises to be useful for a variety of nonlinear optical effects at
the quantum level.Comment: 8 pages, 5 figure
Evolution of induced axial magnetization in a two-component magnetized plasma
In this paper, the evolution of the induced axial magnetization due to the
propagation of an electromagnetic (em) wave along the static background
magnetic field in a two-component plasma has been investigated using the Block
equation. The evolution process induces a strong magnetic anisotropy in the
plasma medium, depending nonlinearly on the incident wave amplitude. This
induced magnetic anisotropy can modify the dispersion relation of the incident
em wave, which has been obtained in this paper. In the low frequency Alfven
wave limit, this dispersion relation shows that the resulting phase velocity of
the incident wave depends on the square of the incident wave amplitude and on
the static background magnetic field of plasma. The analytical results are in
well agreement with the numerically estimated values in solar corona and
sunspots.Comment: 7 pages, 1 figur
Conditional probabilities in quantum theory, and the tunneling time controversy
It is argued that there is a sensible way to define conditional probabilities
in quantum mechanics, assuming only Bayes's theorem and standard quantum
theory. These probabilities are equivalent to the ``weak measurement''
predictions due to Aharonov {\it et al.}, and hence describe the outcomes of
real measurements made on subensembles. In particular, this approach is used to
address the question of the history of a particle which has tunnelled across a
barrier. A {\it gedankenexperiment} is presented to demonstrate the physically
testable implications of the results of these calculations, along with graphs
of the time-evolution of the conditional probability distribution for a
tunneling particle and for one undergoing allowed transmission. Numerical
results are also presented for the effects of loss in a bandgap medium on
transmission and on reflection, as a function of the position of the lossy
region; such loss should provide a feasible, though indirect, test of the
present conclusions. It is argued that the effects of loss on the pulse {\it
delay time} are related to the imaginary value of the momentum of a tunneling
particle, and it is suggested that this might help explain a small discrepancy
in an earlier experiment.Comment: 11 pages, latex, 4 postscript figures separate (one w/ 3 parts
Quantum Nonlocality in Two-Photon Experiments at Berkeley
We review some of our experiments performed over the past few years on
two-photon interference. These include a test of Bell's inequalities, a study
of the complementarity principle, an application of EPR correlations for
dispersion-free time-measurements, and an experiment to demonstrate the
superluminal nature of the tunneling process. The nonlocal character of the
quantum world is brought out clearly by these experiments. As we explain,
however, quantum nonlocality is not inconsistent with Einstein causality.Comment: 16 pages including 24 figure
Comment on "A linear optics implementation of weak values in Hardy's paradox"
A recent experimental proposal by Ahnert and Payne [S.E. Ahnert and M.C.
Payne, Phys. Rev. A 70, 042102 (2004)] outlines a method to measure the weak
value predictions of Aharonov in Hardy's paradox. This proposal contains flaws
such as the state preparation method and the procedure for carrying out the
requisite weak measurements. We identify previously published solutions to some
of the flaws.Comment: To be published in Physical Review
Observation of high-order quantum resonances in the kicked rotor
Quantum resonances in the kicked rotor are characterized by a dramatically
increased energy absorption rate, in stark contrast to the momentum
localization generally observed. These resonances occur when the scaled
Planck's constant hbar=(r/s)*4pi, for any integers r and s. However only the
hbar=r*2pi resonances are easily observable. We have observed high-order
quantum resonances (s>2) utilizing a sample of low temperature, non-condensed
atoms and a pulsed optical standing wave. Resonances are observed for
hbar=(r/16)*4pi r=2-6. Quantum numerical simulations suggest that our
observation of high-order resonances indicates a larger coherence length than
expected from an initially thermal atomic sample
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