295 research outputs found
Atomic interferometer measurements of Berry's and Aharonov-Anandan's phases for isolated spins S > 1/2 non-linearly coupled to external fields
The aim of the present paper is to propose experiments for observing the
significant features of Berry's phases for S>1, generated by spin-Hamiltonians
endowed with two couplings, a magnetic dipole and an electric quadrupole one
with external B and E fields, as theoretically studied in our previous work.
The fields are assumed orthogonal, this mild restriction leading to geometric
and algebraic simplifications. Alkali atoms appear as good candidates for
interferometric measurements but there are challenges to be overcome. The only
practical way to generate a suitable E-field is to use the ac Stark effect
which induces an instability of the dressed atom. Besides atom loss, this might
invalidate Berry's phase derivation but this latter problem can be solved by an
appropriate detuning. The former puts an upper limit to the cycle duration,
which is bounded below by the adiabatic condition. By relying upon our previous
analysis of the non-adiabatic corrections, we have been able to reach a
compromise for the Rb hf level F=2, m=0 state, which is our candidate
for an interferometric measurement of the exotic Berry's phase generated by a
rotation of the E-field around the fixed B-field. By a numerical simulation we
have shown that the non-adiabatic corrections can be kept below the 0.1% level.
As an alternative candidate, we discuss the chromium ground state J=S=3, where
the instability problem is easily solved. We make a proposal to extend the
measurement of Aharonov-Anandan's phase beyond S=1/2 to the Rb hf level
F=m=1, by constructing, with the help of light-shifts, a Hamiltonian able to
perform a parallel transport along a closed circuit upon the density matrix
space, without any adiabatic constraint. In Appendix A, Berry's phase
difference for S=3/2 and 1/2, m=1/2 states is used to perform an entanglement
of 3 Qbits.Comment: 23 pages, 6 figures, modifications in the introduction, two
paragraphs adde
Counting atoms
partially_open2articolo su invitoopenMassa, Enrico; Mana, GiovanniMassa, Enrico; Mana, Giovann
Exact Foldy-Wouthuysen transformation for spin 0 particle in curved space
Up to now, the only known exact Foldy- Wouthuysen transformation (FWT) in
curved space is that concerning Dirac particles coupled to static spacetime
metrics. Here we construct the exact FWT related to a real spin-0 particle for
the aforementioned spacetimes. This exact transformation exists independently
of the value of the coupling between the scalar field and gravity. Moreover,
the gravitational Darwin term written for the conformal coupling is one third
of the relevant term in the fermionic case.Comment: 10 pages, revtex, improved version to appear in Phys. Rev.
SAXS investigations on organic aerogels
Structural properties of organic aerogels were studied by ultra-small-angle X-ray scattering (USAXS) at the Synchrotron Radiation Laboratory HASYLAB at DESY, Hamburg, Germany. The organic aerogels were synthesized from the base-catalyzed sol-gel polymerization of resorcinol with formaldehyde (RF) followed by a supercritical drying process. RF aerogels are low-density materials with a solid matrix composed of interconnected colloidal-like particles. Scattering experiments were carried out using a crystal camera optimized for ultra-small-angle X-ray scattering with synchrotron radiation. The measured SAXS profiles revealed a scattering power depending upon synthetic conditions of the gels. RF aerogels were found to be homogeneous at length scales greater than 20 nm. From Guinier plots, radii of gyration Rg of 3-20 nm were computed. Rg appears to be a measure of the pore (cell) size. Although fractal silica aerogels show similar characteristics, fractal behavior of the organic aerogels is uncertain. These materials are best described as random aggregates of smooth colloidal like particles with open-cell porosity
Pseudo-forces in quantum mechanics
Dynamical evolution is described as a parallel section on an infinite
dimensional Hilbert bundle over the base manifold of all frames of reference.
The parallel section is defined by an operator-valued connection whose
components are the generators of the relativity group acting on the base
manifold. In the case of Galilean transformations we show that the property
that the curvature for the fundamental connection must be zero is just the
Heisenberg equations of motion and the canonical commutation relation in
geometric language. We then consider linear and circular accelerating frames
and show that pseudo-forces must appear naturally in the Hamiltonian.Comment: 6 pages, 1 figure, revtex, new section added, to appear in PR
Does Quantum Mechanics Clash with the Equivalence Principle - and Does it Matter?
With an eye on developing a quantum theory of gravity, many physicists have
recently searched for quantum challenges to the equivalence principle of
general relativity. However, as historians and philosophers of science are well
aware, the principle of equivalence is not so clear. When clarified, we think
quantum tests of the equivalence principle won't yield much. The problem is
that the clash/not-clash is either already evident or guaranteed not to exist.
Nonetheless, this work does help teach us what it means for a theory to be
geometric.Comment: 12 page
Spin, gravity, and inertia
The gravitational effects in the relativistic quantum mechanics are
investigated. The exact Foldy-Wouthuysen transformation is constructed for the
Dirac particle coupled to the static spacetime metric. As a direct application,
we analyze the non-relativistic limit of the theory. The new term describing
the specific spin (gravitational moment) interaction effect is recovered in the
Hamiltonian. The comparison of the true gravitational coupling with the purely
inertial case demonstrates that the spin relativistic effects do not violate
the equivalence principle for the Dirac fermions.Comment: Revtex, 12 pages, no figures, accepted in Phys. Rev. Let
Quantum Theory in Accelerated Frames of Reference
The observational basis of quantum theory in accelerated systems is studied.
The extension of Lorentz invariance to accelerated systems via the hypothesis
of locality is discussed and the limitations of this hypothesis are pointed
out. The nonlocal theory of accelerated observers is briefly described.
Moreover, the main observational aspects of Dirac's equation in noninertial
frames of reference are presented. The Galilean invariance of nonrelativistic
quantum mechanics and the mass superselection rule are examined in the light of
the invariance of physical laws under inhomogeneous Lorentz transformations.Comment: 25 pages, no figures, contribution to Springer Lecture Notes in
Physics (Proc. SR 2005, Potsdam, Germany, February 13 - 18, 2005
Spin-gravity coupling and gravity-induced quantum phases
External gravitational fields induce phase factors in the wave functions of
particles. The phases are exact to first order in the background gravitational
field, are manifestly covariant and gauge invariant and provide a useful tool
for the study of spin-gravity coupling and of the optics of particles in
gravitational or inertial fields. We discuss the role that spin-gravity
coupling plays in particular problems.Comment: 18 pages, 1 figur
Atom Interferometers
Interference with atomic and molecular matter waves is a rich branch of
atomic physics and quantum optics. It started with atom diffraction from
crystal surfaces and the separated oscillatory fields technique used in atomic
clocks. Atom interferometry is now reaching maturity as a powerful art with
many applications in modern science. In this review we first describe the basic
tools for coherent atom optics including diffraction by nanostructures and
laser light, three-grating interferometers, and double wells on AtomChips. Then
we review scientific advances in a broad range of fields that have resulted
from the application of atom interferometers. These are grouped in three
categories: (1) fundamental quantum science, (2) precision metrology and (3)
atomic and molecular physics. Although some experiments with Bose Einstein
condensates are included, the focus of the review is on linear matter wave
optics, i.e. phenomena where each single atom interferes with itself.Comment: submitted to Reviews of Modern Physic
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