11,293 research outputs found
Effect of boundaries on vacuum field fluctuations and radiation-mediated interactions between atoms
In this paper we discuss and review several aspects of the effect of boundary
conditions and structured environments on dispersion and resonance interactions
involving atoms or molecules, as well as on vacuum field fluctuations. We first
consider the case of a perfect mirror, which is free to move around an
equilibrium position and whose mechanical degrees of freedom are treated
quantum mechanically. We investigate how the quantum fluctuations of the
mirror's position affect vacuum field fluctuations for both a one-dimensional
scalar and electromagnetic field, showing that the effect is particularly
significant in the proximity of the moving mirror. This result can be also
relevant for possible gravitational effects, since the field energy density
couples to gravity. We stress that this interaction-induced modification of the
vacuum field fluctuations can be probed through the Casimir-Polder interaction
with a polarizable body, thus allowing to detect the effect of the mirror's
quantum position fluctuations. We then consider the effect of an environment
such as an isotropic photonic crystal or a metallic waveguide, on the resonance
interaction between two entangled identical atoms, one excited and the other in
the ground state. We discuss the strong dependence of the resonance interaction
with the relative position of the atomic transition frequency with the gap of
the photonic crystal in the former case, and with the cut-off frequency of
waveguide in the latter.Comment: 8 pages, 2 figures, Proceedings of the Eighth International Workshop
DICE 2016 Spacetime - Matter - Quantum Mechanic
Fluctuating noise drives Brownian transport
The transport properties of Brownian ratchet was studied in the presence of
stochastic intensity noise (SIN) in both overdamped and underdamped regimes. In
the overdamped case, analytical solution using the matrix continued fraction
method revealed the existence of a maximum current when the noise intensity
fluctuates on intermediate time scale regions. Similar effects were observed
for the underdamped case by Monte Carlo simulations. The optimal
time-correlation for the Brownian transport coincided with the experimentally
observed time-correlation of the extrinsic noise in Esherichia coli gene
expression and implied the importance of environmental noise for molecular
mechanisms.Comment: 22 pages, 8 figure
Van der Waals and resonance interactions between accelerated atoms in vacuum and the Unruh effect
We discuss different physical effects related to the uniform acceleration of
atoms in vacuum, in the framework of quantum electrodynamics. We first
investigate the van der Waals/Casimir-Polder dispersion and resonance
interactions between two uniformly accelerated atoms in vacuum. We show that
the atomic acceleration significantly affects the van der Waals force, yielding
a different scaling of the interaction with the interatomic distance and an
explicit time dependence of the interaction energy. We argue how these results
could allow for an indirect detection of the Unruh effect through dispersion
interactions between atoms. We then consider the resonance interaction between
two accelerated atoms, prepared in a correlated Bell-type state, and
interacting with the electromagnetic field in the vacuum state, separating
vacuum fluctuations and radiation reaction contributions, both in the
free-space and in the presence of a perfectly reflecting plate. We show that
nonthermal effects of acceleration manifest in the resonance interaction,
yielding a change of the distance dependence of the resonance interaction
energy. This suggests that the equivalence between temperature and acceleration
does not apply to all radiative properties of accelerated atoms. To further
explore this aspect, we evaluate the resonance interaction between two atoms in
non inertial motion in the coaccelerated (Rindler) frame and show that in this
case the assumption of an Unruh temperature for the field is not required for a
complete equivalence of locally inertial and coaccelerated points of views.Comment: 8 pages, Proceedings of the Eighth International Workshop DICE 2016
Spacetime - Matter - Quantum Mechanic
Field fluctuations near a conducting plate and Casimir-Polder forces in the presence of boundary conditions
We consider vacuum fluctuations of the quantum electromagnetic field in the
presence of an infinite and perfectly conducting plate. We evaluate how the
change of vacuum fluctuations due to the plate modifies the Casimir-Polder
potential between two atoms placed near the plate. We use two different methods
to evaluate the Casimir-Polder potential in the presence of the plate. They
also give new insights on the role of boundary conditions in the Casimir-Polder
interatomic potential, as well as indications for possible generalizations to
more complicated boundary conditions.Comment: 10 page
Anomalous lack of decoherence of the Macroscopic Quantum Superpositions based on phase-covariant Quantum Cloning
We show that all Macroscopic Quantum Superpositions (MQS) based on
phase-covariant quantum cloning are characterized by an anomalous high
resilence to the de-coherence processes. The analysis supports the results of
recent MQS experiments and leads to conceive a useful conjecture regarding the
realization of complex decoherence - free structures for quantum information,
such as the quantum computer.Comment: 4 pages, 3 figure
Mean Escape Time in a System with Stochastic Volatility
We study the mean escape time in a market model with stochastic volatility.
The process followed by the volatility is the Cox Ingersoll and Ross process
which is widely used to model stock price fluctuations. The market model can be
considered as a generalization of the Heston model, where the geometric
Brownian motion is replaced by a random walk in the presence of a cubic
nonlinearity. We investigate the statistical properties of the escape time of
the returns, from a given interval, as a function of the three parameters of
the model. We find that the noise can have a stabilizing effect on the system,
as long as the global noise is not too high with respect to the effective
potential barrier experienced by a fictitious Brownian particle. We compare the
probability density function of the return escape times of the model with those
obtained from real market data. We find that they fit very well.Comment: 9 pages, 9 figures, to be published in Phys. Rev.
Glare, a GIS tool to reconstruct the 3D surface of palaeoglaciers
Acknowledgements This research has been supported by the Leverhulme Trust International Network Grant IN-2012-140. Processing and collecting of ground penetrating data in Forgefonna was part of Elend Førre's master's project that was completed in 2009 at the Department of Geography, University of Bergen. We also acknowledge Dr Andreas Bauder for providing the subglacial topography data for Griessgletscher and Simone Tarquini for granting access to the high resolution TIN of Italy, a cut of which is provided to the reader to practice the tools (see Appendix). Referees Dr. Iestyn Barr, Dr. Jeremy Ely and Dr. Marc Oliva are thanked for their constructive comments and tool testing, which significantly improved the final output.Peer reviewedPostprin
General rules for bosonic bunching in multimode interferometers
We perform a comprehensive set of experiments that characterize bosonic
bunching of up to 3 photons in interferometers of up to 16 modes. Our
experiments verify two rules that govern bosonic bunching. The first rule,
obtained recently in [1,2], predicts the average behavior of the bunching
probability and is known as the bosonic birthday paradox. The second rule is
new, and establishes a n!-factor quantum enhancement for the probability that
all n bosons bunch in a single output mode, with respect to the case of
distinguishable bosons. Besides its fundamental importance in phenomena such as
Bose-Einstein condensation, bosonic bunching can be exploited in applications
such as linear optical quantum computing and quantum-enhanced metrology.Comment: 6 pages, 4 figures, and supplementary material (4 pages, 1 figure
Casimir-Polder interatomic potential between two atoms at finite temperature and in the presence of boundary conditions
We evaluate the Casimir-Polder potential between two atoms in the presence of
an infinite perfectly conducting plate and at nonzero temperature. In order to
calculate the potential, we use a method based on equal-time spatial
correlations of the electric field, already used to evaluate the effect of
boundary conditions on interatomic potentials. This method gives also a
transparent physical picture of the role of a finite temperature and boundary
conditions on the Casimir-Polder potential. We obtain an analytical expression
of the potential both in the near and far zones, and consider several limiting
cases of interest, according to the values of the parameters involved, such as
atom-atom distance, atoms-wall distance and temperature.Comment: 11 page
- …