777 research outputs found
Dynamical Casimir-Polder energy between an excited and a ground-state atom
We consider the Casimir-Polder interaction between two atoms, one in the
ground state and the other in its excited state. The interaction is
time-dependent for this system, because of the dynamical self-dressing and the
spontaneous decay of the excited atom. We calculate the dynamical
Casimir-Polder potential between the two atoms using an effective Hamiltonian
approach. The results obtained and their physical meaning are discussed and
compared with previous results based on a time-independent approach which uses
a non-normalizable dressed state for the excited atom.Comment: 11 page
Non locality and causal evolution in QFT
Non locality appearing in QFT during the free evolution of localized field
states and in the Feynman propagator function is analyzed. It is shown to be
connected to the initial non local properties present at the level of quantum
states and then it does not imply a violation of Einstein's causality. Then it
is investigated a simple QFT system with interaction, consisting of a classical
source coupled linearly to a quantum scalar field, that is exactly solved. The
expression for the time evolution of the state describing the system is given.
The expectation value of any arbitrary ``good'' local observable, expressed as
a function of the field operator and its space and time derivatives, is
obtained explicitly at all order in the field-matter coupling constant. These
expectation values have a source dependent part that is shown to be always
causally retarded, while the non local contributions are source independent and
related to the non local properties of zero point vacuum fluctuations.Comment: Submitted to Journal of Physics B: 16 pages: 1 figur
Geometric phase for an accelerated two-level atom and the Unruh effect
We study, in the framework of open quantum systems, the geometric phase
acquired by a uniformly accelerated two-level atom undergoing nonunitary
evolution due to its coupling to a bath of fluctuating vacuum electromagnetic
fields in the multipolar scheme. We find that the phase variation due to the
acceleration can be in principle observed via atomic interferometry between the
accelerated atom and the inertial one, thus providing an evidence of the Unruh
effect.Comment: 12 pages, no figure
Comment on 'Self-dressing and radiation reaction in classical electrodynamics'
Using the canonical formalism, Compagno and Persico [J. Phys. A: Math. Gen.
35 (2002) 3629--45] have calculated the 'radiation-reaction' force on a uniform
spherical charge moving rigidly, slowly and slightly from its position at the
time when the transverse electric field is assumed to vanish. This force is
shown to result in the same time-averaged self-force as that which has been
obtained by different means for the test charge of a Bohr--Rosenfeld
field-measurement procedure and which Compagno and Persico claimed to be
incorrect.Comment: REVTeX, 4 pages; this version has some cosmetic changes to agree
fully with the published version. Reply to this Comment is in G. Compagno and
F. Persico, J. Phys. A: Math. Gen. 35, 8965 (2002); response to the Reply is
in physics/021005
Non-local quantum correlations and detection processes in QFT
Quantum detection processes in QFT must play a key role in the description of
quantum field correlations, such as the appearance of entanglement, and of
causal effects. We consider the detection in the case of a simple QFT model
with a suitable interaction to exact treatment, consisting of a quantum scalar
field coupled linearly to a classical scalar source. We then evaluate the
response function to the field quanta of two-level point-like quantum model
detectors, and analyze the effects of the approximation adopted in standard
detection theory. We show that the use of the RWA, that characterizes the
Glauber detection model, leads in the detector response to non-local terms
corresponding to an instantaneously spreading of source effects over the whole
space. Other detector models, obtained with non-standard or the no-application
of RWA, give instead local responses to field quanta, apart from source
independent vacuum contribution linked to preexisting correlations of
zero-point field.Comment: 23 page
Entanglement degradation in the solid state: interplay of adiabatic and quantum noise
We study entanglement degradation of two non-interacting qubits subject to
independent baths with broadband spectra typical of solid state nanodevices. We
obtain the analytic form of the concurrence in the presence of adiabatic noise
for classes of entangled initial states presently achievable in experiments. We
find that adiabatic (low frequency) noise affects entanglement reduction
analogously to pure dephasing noise. Due to quantum (high frequency) noise,
entanglement is totally lost in a state-dependent finite time. The possibility
to implement on-chip both local and entangling operations is briefly discussed.Comment: Replaced with published version. Minor change
Causality and Localization Operators
The evolution of the expectation values of one and two points scalar field
operators and of positive localization operators, generated by an istantaneous
point source is non local. Non locality is attributed either to zero point
vacuum fluctuations, or to non local operations or to the microcausality
principle being no satisfied.Comment: 10 pages; submitted to Physics Letters
Fluctuations of the Casimir-Polder force between an atom and a conducting wall
We consider the quantum fluctuations of the Casimir-Polder force between a
neutral atom and a perfectly conducting wall in the ground state of the system.
In order to obtain the atom-wall force fluctuation we first define an operator
directly associated to the force experienced by the atom considered as a
polarizable body in an electromagnetic field, and we use a time-averaged force
operator in order to avoid ultraviolet divergences appearing in the fluctuation
of the force. This time-averaged force operator takes into account that any
measurement involves a finite time. We also calculate the Casimir-Polder force
fluctuation for an atom between two conducting walls. Experimental
observability of these Casimir-Polder force fluctuations is also discussed, as
well as the dependence of the relative force fluctuation on the duration of the
measurement.Comment: 6 page
Casimir-Polder potentials as entanglement probe
We have considered the interaction of a pair of spatially separated two-level
atoms with the electromagnetic field in its vacuum state and we have analyzed
the amount of entanglement induced between the two atoms by the non local field
fluctuations. This has allowed us to characterize the quantum nature of the non
local correlations of the electromagnetic field vacuum state as well as to link
the induced quantum entanglement with Casimir-Polder potentials.Comment: Published on Europhysics Letters 78 (2007) 3000
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