150 research outputs found
Gravitational Decoherence
We discuss effects of loss of coherence in low energy quantum systems caused
by or related to gravitation, referred to as gravitational decoherence. These
effects, resulting from random metric fluctuations, for instance, promise to be
accessible by relatively inexpensive table-top experiments, way before the
scales where true quantum gravity effects become important. Therefore, they can
provide a first experimental view on gravity in the quantum regime. We will
survey models of decoherence induced both by classical and quantum
gravitational fluctuations; it will be manifest that a clear understanding of
gravitational decoherence is still lacking. Next we will review models where
quantum theory is modified, under the assumption that gravity causes the
collapse of the wave functions, when systems are large enough. These models
challenge the quantum-gravity interplay, and can be tested experimentally. In
the last part we have a look at the state of the art of experimental research.
We will review efforts aiming at more and more accurate measurements of gravity
(G and g) and ideas for measuring conventional and unconventional gravity
effects on nonrelativistic quantum systems.Comment: Invited topical review article for Classical and Quantum Gravity, 78
page
Physisorption of molecular oxygen on single-wall carbon nanotube bundles and graphite
We present a study on the kinetics of oxygen adsorption and desorption from
single-wall carbon nanotube (SWNT) and highly oriented pyrolytic graphite
(HOPG) samples. Thermal desorption spectra for SWNT samples show a broad
desorption feature peaked at 62 K which is shifted to significantly higher
temperature than the low-coverage desorption feature on HOPG. The low-coverage
O2 binding energy on SWNT bundles, 18.5 kJ/mol, is 55% higher than that for
adsorption on HOPG, 12.0 kJ/mol. In combination with molecular mechanics
calculations we show that the observed binding energies for both systems can be
attributed to van der Waals interactions, i.e. physisorption. The experiments
provide no evidence for a more strongly bound chemisorbed species or for
dissociative oxygen adsorption.Comment: 7 pages, 5 figures, 1 tabl
Wigner Function Reconstruction in Levitated Optomechanics
We demonstrate the reconstruction of the Wigner function from marginal
distributions of the motion of a single trapped particle using homodyne
detection. We show that it is possible to generate quantum states of levitated
optomechanical systems even under the effect of continuous measurement by the
trapping laser light. We describe the opto-mechanical coupling for the case of
the particle trapped by a free-space focused laser beam, explicitly for the
case without an optical cavity. We use the scheme to reconstruct the Wigner
function of experimental data in perfect agreement with the expected Gaussian
distribution of a thermal state of motion. This opens a route for quantum state
preparation in levitated optomechanics.Comment: 9 pages, 3 figure
Macroscopicity in an optomechanical matter-wave interferometer
We analyse a proposal that we have recently put forward for an interface
between matter-wave and optomechanical technologies from the perspective of
macroscopic quantumness. In particular, by making use of a measure of
macroscopicity in quantum superpositions that is particularly well suited for
continuous variables systems, we demonstrate the existence of working points
for our interface at which a quantum mechanical superposition of genuinely
mesoscopic states is achieved. Our proposal thus holds the potential to affirm
itself as a viable atom-to-mechanics transducer of quantum coherences.Comment: Accepted for publication in Optics Communications, special issue on
"Macroscopic Quantumness: Theory and Applications in Optical Sciences
Effects of Newtonian gravitational self-interaction in harmonically trapped quantum systems
The Schr\"odinger-Newton equation has gained attention in the recent past as
a nonlinear modification of the Schr\"odinger equation due to a gravitational
self-interaction. Such a modification is expected from a fundamentally
semi-classical theory of gravity, and can therefore be considered a test case
for the necessity of the quantisation of the gravitational field. Here we
provide a thorough study of the effects of the Schr\"odinger-Newton equation
for a micron-sized sphere trapped in a harmonic oscillator potential. We
discuss both the effect on the energy eigenstates and the dynamical behaviour
of squeezed states, covering the experimentally relevant parameter regimes.Comment: 22 pages, 14 figure
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