41,710 research outputs found
Quantum chaos: an introduction via chains of interacting spins-1/2
We introduce aspects of quantum chaos by analyzing the eigenvalues and the
eigenstates of quantum many-body systems. The properties of quantum systems
whose classical counterparts are chaotic differ from those whose classical
counterparts are not chaotic. The spectrum of the first exhibits repulsion of
the energy levels. This is one of the main signatures of quantum chaos. We show
how level repulsion develops in one-dimensional systems of interacting spins
1/2 which are devoid of random elements and involve only two-body interactions.
In addition to the statistics of the eigenvalues, we analyze how the structure
of the eigenstates may indicate chaos. The programs used to obtain the data are
available online.Comment: 7 pages, 3 figure
Cold atoms in non-Abelian gauge potentials: From the Hofstadter "moth" to lattice gauge theory
We demonstrate how to create artificial external non-Abelian gauge potentials
acting on cold atoms in optical lattices. The method employs internal
states of atoms and laser assisted state sensitive tunneling. Thus, dynamics
are communicated by unitary -matrices. By experimental control of
the tunneling parameters, the system can be made truly non-Abelian. We show
that single particle dynamics in the case of intense U(2) vector potentials
lead to a generalized Hofstadter butterfly spectrum which shows a complex
``moth''-like structure. We discuss the possibility to employ non-Abelian
interferometry (Aharonov-Bohm effect) and address methods to realize matter
dynamics in specific classes of lattice gauge fields.Comment: 5 pages, 3 figure
Mapping case studies of public engagement and participation in science and technology
In recent years, increasing criticism has been levelled against case study based research on public
engagement and participation in science and technology (PEST). Most critics argue that such
case studies are highly contextual and fail to provide global, holistic and systemic views of public
engagement phenomena. In this study, we mapped the case study literature on PEST by identifying a
robust sample of articles, and analysed it looking for emerging patterns that could provide empirical
evidence for new frameworks of public engagement design and analysis. Results show that the case
study based literature on PEST continues to grow, although concentrated in a few countries and
knowledge domains. The trends that emerged from the sample reveal high centralisation and planning
and suggest that deficit science communication models are still common. We argue that future
frameworks may focus on decentralising hierarchical power and dependency relationships between
agents.info:eu-repo/semantics/publishedVersio
A Flexible Implementation of a Matrix Laurent Series-Based 16-Point Fast Fourier and Hartley Transforms
This paper describes a flexible architecture for implementing a new fast
computation of the discrete Fourier and Hartley transforms, which is based on a
matrix Laurent series. The device calculates the transforms based on a single
bit selection operator. The hardware structure and synthesis are presented,
which handled a 16-point fast transform in 65 nsec, with a Xilinx SPARTAN 3E
device.Comment: 4 pages, 4 figures. IEEE VI Southern Programmable Logic Conference
201
Reversible quantum teleportation in an optical lattice
We propose a protocol, based on entanglement procedures recently suggested by
[D. Jaksch et al., Phys. Rev. Lett. 82, 1975 (1999)], which allows the
teleportation of an unknown state of a neutral atom in an optical lattice to
another atom in another site of the lattice, without any irreversible
detection.Comment: 8 pages, 3 figure
Controlling the dynamics of a coupled atom-cavity system by pure dephasing : basics and potential applications in nanophotonics
The influence of pure dephasing on the dynamics of the coupling between a
two-level atom and a cavity mode is systematically addressed. We have derived
an effective atom-cavity coupling rate that is shown to be a key parameter in
the physics of the problem, allowing to generalize the known expression for the
Purcell factor to the case of broad emitters, and to define strategies to
optimize the performances of broad emitters-based single photon sources.
Moreover, pure dephasing is shown to be able to restore lasing in presence of
detuning, a further demonstration that decoherence can be seen as a fundamental
resource in solid-state cavity quantum electrodynamics, offering appealing
perspectives in the context of advanced nano-photonic devices.Comment: 10 pages, 7 figure
Mass-degenerate Higgs bosons at 125 GeV in the Two-Higgs-Doublet Model
The analysis of the Higgs boson data by the ATLAS and CMS Collaborations
appears to exhibit an excess of h --> gamma\gamma events above the Standard
Model (SM) expectations; whereas no significant excess is observed in h --> ZZ*
--> {four lepton} events, albeit with large statistical uncertainty due to the
small data sample. These results (assuming they persist with further data)
could be explained by a pair of nearly mass-degenerate scalars, one of which is
a SM-like Higgs boson and the other is a scalar with suppressed couplings to
W+W- and ZZ. In the two Higgs doublet model, the observed \gamma\gamma and ZZ*
--> {four lepton} data can be reproduced by an approximately degenerate CP-even
(h) and CP-odd (A) Higgs boson for values of \sin(\beta-\alpha) near unity and
0.7 < \tan\beta < 1. An enhanced \gamma\gamma signal can also arise in cases
where m_h ~ m_H, m_H ~ m_A, or m_h ~ m_H ~ m_A. Since the ZZ* --> {four lepton}
signal derives primarily from a SM-like Higgs boson whereas the \gamma\gamma
signal receives contributions from two (or more) nearly mass-degenerate states,
one would expect a slightly different invariant mass peak in the ZZ* --> {four
lepton} and \gamma\gamma channels. The phenomenological consequences of such
models can be tested with additional Higgs data that will be collected at the
LHC in the near future.Comment: 18 pages, 19 pdf figures, v2: references added, v3&v4: added refs and
explanation
Conservation of Orbital Angular Momentum in Stimulated Down-Conversion
We report on an experiment demonstrating the conservation of orbital angular
momentum in stimulated down-conversion. The orbital angular momentum is not
transferred to the individual beams of the spontaneous down-conversion, but it
is conserved when twin photons are taken individually. We observe the
conservation law for an individual beam of the down-conversion through
cavity-free stimulated emission.Comment: Submitted for publication in Phys. Rev. Let
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