1,477 research outputs found
Measurement of a Mixed Spin Channel Feshbach Resonance in Rubidium 87
We report on the observation of a mixed spin channel Feshbach resonance at
the low magnetic field value of (9.09 +/- 0.01) G for a mixture of |2,-1> and
|1,+1> states in 87Rb. This mixture is important for applications of
multi-component BECs of 87Rb, e.g. in spin mixture physics and for quantum
entanglement. Values for position, height and width of the resonance are
reported and compared to a recent theoretical calculation of this resonance.Comment: 4 pages, 3 figures minor changes, actualized citation
The Superposition Principle of Waves Not Fulfilled under M. W. Evans' O(3) Hypothesis
In 1992 M.W. Evans proposed a so-called O(3) symmetry of electromagnetic
fields by adding a constant longitudinal "ghost field" to the well-known
transversal plane em waves. He considered this symmetry as a new law of
electromagnetics. Later on, since 2002, this O(3) symmetry became the center of
his Generally Covariant Unified Field Theory which he recently renamed as ECE
Theory. One of the best-checked laws of electrodynamics is the principle of
linear superposition of electromagnetic waves, manifesting itself in
interference phenomena. Its mathematical equivalent is the representation of
electric and magnetic fields as vectors. By considering the superposition of
two phase-shifted waves we show that the superposition principle is
incompatible with M.W. Evans' O(3) hypothesis.Comment: 5 pages, no figure
Bose-Einstein condensation at constant temperature
We present a novel experimental approach to Bose-Einstein condensation by
increasing the particle number of the system at almost constant temperature. In
particular the emergence of a new condensate is observed in multi-component F=1
spinor condensates of 87-Rb. Furthermore we develop a simple rate-equation
model for multi-component BEC thermodynamics at finite temperature which well
reproduces the measured effects.Comment: 4 pages, 3 figures, RevTe
Extensions and block decompositions for finite-dimensional representations of equivariant map algebras
Suppose a finite group acts on a scheme and a finite-dimensional Lie
algebra . The associated equivariant map algebra is the Lie
algebra of equivariant regular maps from to . The irreducible
finite-dimensional representations of these algebras were classified in
previous work with P. Senesi, where it was shown that they are all tensor
products of evaluation representations and one-dimensional representations. In
the current paper, we describe the extensions between irreducible
finite-dimensional representations of an equivariant map algebra in the case
that is an affine scheme of finite type and is reductive.
This allows us to also describe explicitly the blocks of the category of
finite-dimensional representations in terms of spectral characters, whose
definition we extend to this general setting. Applying our results to the case
of generalized current algebras (the case where the group acting is trivial),
we recover known results but with very different proofs. For (twisted) loop
algebras, we recover known results on block decompositions (again with very
different proofs) and new explicit formulas for extensions. Finally,
specializing our results to the case of (twisted) multiloop algebras and
generalized Onsager algebras yields previously unknown results on both
extensions and block decompositions.Comment: 41 pages; v2: minor corrections, formatting changed to match
published versio
Optical control of internal electric fields in band-gap graded InGaN nanowires
InGaN nanowires are suitable building blocks for many future optoelectronic
devices. We show that a linear grading of the indium content along the nanowire
axis from GaN to InN introduces an internal electric field evoking a
photocurrent. Consistent with quantitative band structure simulations we
observe a sign change in the measured photocurrent as a function of photon
flux. This negative differential photocurrent opens the path to a new type of
nanowire-based photodetector. We demonstrate that the photocurrent response of
the nanowires is as fast as 1.5 ps
Dynamics of F=2 Spinor Bose-Einstein Condensates
We experimentally investigate and analyze the rich dynamics in F=2 spinor
Bose-Einstein condensates of Rb87. An interplay between mean-field driven spin
dynamics and hyperfine-changing losses in addition to interactions with the
thermal component is observed. In particular we measure conversion rates in the
range of 10^-12 cm^3/s for spin changing collisions within the F=2 manifold and
spin-dependent loss rates in the range of 10^-13 cm^3/s for hyperfine-changing
collisions. From our data we observe a polar behavior in the F=2 ground state
of Rb87, while we measure the F=1 ground state to be ferromagnetic. Furthermore
we see a magnetization for condensates prepared with non-zero total spin.Comment: 4 pages, 2 figures, RevTe
A Model for QCD at High Density and Large Quark Mass
We study the high density region of QCD within an effective model obtained in
the frame of the hopping parameter expansion and choosing Polyakov type of
loops as the main dynamical variables representing the fermionic matter. To get
a first idea of the phase structure, the model is analyzed in strong coupling
expansion and using a mean field approximation. In numerical simulations, the
model still shows the so-called sign problem, a difficulty peculiar to non-zero
chemical potential, but it permits the development of algorithms which ensure a
good overlap of the Monte Carlo ensemble with the true one. We review the main
features of the model and present calculations concerning the dependence of
various observables on the chemical potential and on the temperature, in
particular of the charge density and the diquark susceptibility, which may be
used to characterize the various phases expected at high baryonic density. We
obtain in this way information about the phase structure of the model and the
corresponding phase transitions and cross over regions, which can be considered
as hints for the behaviour of non-zero density QCD.Comment: 21 pages, 29 figure
Quantum indistinguishability by path identity and with undetected photons
Two processes of photon-pair creation can be arranged such that the paths of the emitted photons are identical. The path information is thereby not erased but rather never born in the first place due to this path identity. In addition to its implications for fundamental physics, this concept has recently led to a series of impactful discoveries in the fields of imaging, spectroscopy, and quantum information science. Here the idea of path identity is presented and a comprehensive review of recent developments is provided. Specifically, the concept of path identity is introduced based on three defining experimental ideas from the early 1990s. The three experiments have in common that they contain two photon-pair sources. The paths of one or both photons from the different sources overlap such that no measurement can recognize from which source they originate. A wide range of noteworthy quantum interference effects (at the single- or two-photon level), such as induced coherence, destructive interference of photon pairs, and entanglement generation, are subsequently described. Progress in the exploration of these ideas has stagnated and has gained momentum again only in the last few years. The focus of the review is the new development in the last few years that modified and generalized the ideas from the early 1990s. These developments are overviewed and explained under the same conceptual umbrella, which will help the community develop new applications and realize the foundational implications of this sleeping beauty
Real-time dynamics of lattice gauge theories with a few-qubit quantum computer
Gauge theories are fundamental to our understanding of interactions between
the elementary constituents of matter as mediated by gauge bosons. However,
computing the real-time dynamics in gauge theories is a notorious challenge for
classical computational methods. In the spirit of Feynman's vision of a quantum
simulator, this has recently stimulated theoretical effort to devise schemes
for simulating such theories on engineered quantum-mechanical devices, with the
difficulty that gauge invariance and the associated local conservation laws
(Gauss laws) need to be implemented. Here we report the first experimental
demonstration of a digital quantum simulation of a lattice gauge theory, by
realising 1+1-dimensional quantum electrodynamics (Schwinger model) on a
few-qubit trapped-ion quantum computer. We are interested in the real-time
evolution of the Schwinger mechanism, describing the instability of the bare
vacuum due to quantum fluctuations, which manifests itself in the spontaneous
creation of electron-positron pairs. To make efficient use of our quantum
resources, we map the original problem to a spin model by eliminating the gauge
fields in favour of exotic long-range interactions, which have a direct and
efficient implementation on an ion trap architecture. We explore the Schwinger
mechanism of particle-antiparticle generation by monitoring the mass production
and the vacuum persistence amplitude. Moreover, we track the real-time
evolution of entanglement in the system, which illustrates how particle
creation and entanglement generation are directly related. Our work represents
a first step towards quantum simulating high-energy theories with atomic
physics experiments, the long-term vision being the extension to real-time
quantum simulations of non-Abelian lattice gauge theories
Reply to David's Comment on ``Superinstantons and the Reliability of Perturbation Theory in Non-Abelian Models''
We reply to David's comment (hep-lat/9504017) on our paper Phys.Rev.Lett.
74(1995)1920.Comment: 2 pages, latex, no figure
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