292 research outputs found
Counting atoms
partially_open2articolo su invitoopenMassa, Enrico; Mana, GiovanniMassa, Enrico; Mana, Giovann
X-ray Near Field Speckle: Implementation and Critical Analysis
We have implemented the newly-introduced, coherence-based technique of x-ray
near-field speckle (XNFS) at 8-ID-I at the Advanced Photon Source. In the near
field regime of high-brilliance synchrotron x-rays scattered from a sample of
interest, it turns out, that, when the scattered radiation and the main beam
both impinge upon an x-ray area detector, the measured intensity shows
low-contrast speckles, resulting from interference between the incident and
scattered beams. We built a micrometer-resolution XNFS detector with a high
numerical aperture microscope objective and demonstrate its capability for
studying static structures and dynamics at longer length scales than
traditional far field x-ray scattering techniques. Specifically, we
characterized the structure and dynamics of dilute silica and polystyrene
colloidal samples. Our study reveals certain limitations of the XNFS technique,
which we discuss.Comment: 53 pages, 16 figure
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
Lithium atom interferometer using laser diffraction : description and experiments
We have built and operated an atom interferometer of the Mach-Zehnder type.
The atomic wave is a supersonic beam of lithium seeded in argon and the mirrors
and beam-splitters for the atomic wave are based on elastic Bragg diffraction
on laser standing waves at 671 nm. We give here a detailed description of our
experimental setup and of the procedures used to align its components. We then
present experimental signals, exhibiting atomic interference effects with a
very high visibility, up to 84.5 %. We describe a series of experiments testing
the sensitivity of the fringe visibility to the main alignment defects and to
the magnetic field gradient.Comment: 8 avril 200
Decoherence, fluctuations and Wigner function in neutron optics
We analyze the coherence properties of neutron wave packets, after they have
interacted with a phase shifter undergoing different kinds of statistical
fluctuations. We give a quantitative (and operational) definition of
decoherence and compare it to the standard deviation of the distribution of the
phase shifts. We find that in some cases the neutron ensemble is more coherent,
even though it has interacted with a wider (i.e. more disordered) distribution
of shifts. This feature is independent of the particular definition of
decoherence: this is shown by proposing and discussing an alternative
definition, based on the Wigner function, that displays a similar behavior. We
briefly discuss the notion of entropy of the shifts and find that, in general,
it does not correspond to that of decoherence of the neutron.Comment: 18 pages, 7 figure
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
Quantum systems in weak gravitational fields
Fully covariant wave equations predict the existence of a class of
inertial-gravitational effects that can be tested experimentally. In these
equations inertia and gravity appear as external classical fields, but, by
conforming to general relativity, provide very valuable information on how
Einstein's views carry through in the world of the quantum.Comment: 22 pages. To be published in Proceedings of the 17th Course of the
International School of Cosmology and Gravitation "Advances in the interplay
between quantum and gravity physics" edited by V. De Sabbata and A.
Zheltukhin, Kluwer Academic Publishers, Dordrech
Spallative ablation of dielectrics by X-ray laser
Short laser pulse in wide range of wavelengths, from infrared to X-ray,
disturbs electron-ion equilibrium and rises pressure in a heated layer. The
case where pulse duration is shorter than acoustic relaxation time
is considered in the paper. It is shown that this short pulse may cause
thermomechanical phenomena such as spallative ablation regardless to
wavelength. While the physics of electron-ion relaxation on wavelength and
various electron spectra of substances: there are spectra with an energy gap in
semiconductors and dielectrics opposed to gapless continuous spectra in metals.
The paper describes entire sequence of thermomechanical processes from
expansion, nucleation, foaming, and nanostructuring to spallation with
particular attention to spallation by X-ray pulse
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
- …