2,586 research outputs found
Problems with the Newton-Schr\"odinger Equations
We examine the origin of the Newton-Schr\"odinger equations (NSEs) that play
an important role in alternative quantum theories (AQT), macroscopic quantum
mechanics and gravity-induced decoherence. We show that NSEs for individual
particles do not follow from general relativity (GR) plus quantum field theory
(QFT). Contrary to what is commonly assumed, the NSEs are not the weak-field
(WF), non-relativistic (NR) limit of the semi-classical Einstein equation (SCE)
(this nomenclature is preferred over the `M\/oller-Rosenfeld equation') based
on GR+QFT. The wave-function in the NSEs makes sense only as that for a mean
field describing a system of particles as , not that
of a single or finite many particles. From GR+QFT the gravitational
self-interaction leads to mass renormalization, not to a non-linear term in the
evolution equations of some AQTs. The WF-NR limit of the gravitational
interaction in GR+QFT involves no dynamics. To see the contrast, we give a
derivation of the equation (i) governing the many-body wave function from
GR+QFT and (ii) for the non-relativistic limit of quantum electrodynamics
(QED). They have the same structure, being linear, and very different from
NSEs. Adding to this our earlier consideration that for gravitational
decoherence the master equations based on GR+QFT lead to decoherence in the
energy basis and not in the position basis, despite some AQTs desiring it for
the `collapse of the wave function', we conclude that the origins and
consequences of NSEs are very different, and should be clearly demarcated from
those of the SCE equation, the only legitimate representative of semiclassical
gravity, based on GR+QFT.Comment: 18 pages. Invited paper for the Focus Issue on 'Gravitational quantum
physics' in New Journal of Physic
Non-Equilibrium Quantum Electrodynamics
We employ the influence functional technique to trace out the photonic
contribution from full quantum electrodynamics. The reduced density matrix
propagator for the spinor field is then constructed. We discuss the role of
time-dependent renormalization in the propagator and focus on the possibility
of obtaining dynamically induced superselection rules. Finally, we derive the
master equation for the case of the field being in an one-particle state in a
non-relativistic regime and discuss whether EM vacuumm fluctuations are
sufficient to produce decoherence in the position basis.Comment: 28 pages, 2 figures. Substantially revised, one important mistake
corrected; discussion on decoherence upgraded, section 4 essentially
rewritte
Gravitational decoherence: A thematic overview
Gravitational decoherence (GD) refers to the effects of gravity in actuating the classical appearance of a quantum system. Because the underlying processes involve issues in general relativity (GR), quantum field theory (QFT), and quantum information, GD has fundamental theoretical significance. There is a great variety of GD models, many of them involving physics that diverge from GR and/or QFT. This overview has two specific goals along with one central theme:(i) present theories of GD based on GR and QFT and explore their experimental predictions;(ii) place other theories of GD under the scrutiny of GR and QFT, and point out their theoretical differences. We also describe how GD experiments in space in the coming decades can provide evidence at two levels:(a) discriminate alternative quantum theories and non-GR theories;(b) discern whether gravity is a fundamental or an effective theory
Decoherence in Quantum Gravity: Issues and Critiques
An increasing number of papers have appeared in recent years on decoherence
in quantum gravity at the Planck energy. We discuss the meaning of decoherence
in quantum gravity starting from the common notion that quantum gravity is a
theory for the microscopic structures of spacetime, and invoking some generic
features of quantum decoherence from the open systems viewpoint. We dwell on a
range of issues bearing on this process including the relation between
statistical and quantum, noise from effective field theory, the meaning of
stochasticity, the origin of non-unitarity and the nature of nonlocality in
this and related contexts. To expound these issues we critique on two
representative theories: One claims that decoherence in quantum gravity scale
leads to the violation of CPT symmetry at sub-Planckian energy which is used to
explain today's particle phenomenology. The other uses this process in place
with the Brownian motion model to prove that spacetime foam behaves like a
thermal bath.Comment: 25 pages, proceedings of DICE06 (Piombino
Non-Markovian Dynamics and Entanglement of Two-level Atoms in a Common Field
We derive the stochastic equations and consider the non-Markovian dynamics of
a system of multiple two-level atoms in a common quantum field. We make only
the dipole approximation for the atoms and assume weak atom-field interactions.
From these assumptions we use a combination of non-secular open- and
closed-system perturbation theory, and we abstain from any additional
approximation schemes. These more accurate solutions are necessary to explore
several regimes: in particular, near-resonance dynamics and low-temperature
behavior. In detuned atomic systems, small variations in the system energy
levels engender timescales which, in general, cannot be safely ignored, as
would be the case in the rotating-wave approximation (RWA). More problematic
are the second-order solutions, which, as has been recently pointed out, cannot
be accurately calculated using any second-order perturbative master equation,
whether RWA, Born-Markov, Redfield, etc.. This latter problem, which applies to
all perturbative open-system master equations, has a profound effect upon
calculation of entanglement at low temperatures. We find that even at zero
temperature all initial states will undergo finite-time disentanglement
(sometimes termed "sudden death"), in contrast to previous work. We also use
our solution, without invoking RWA, to characterize the necessary conditions
for Dickie subradiance at finite temperature. We find that the subradiant
states fall into two categories at finite temperature: one that is temperature
independent and one that acquires temperature dependence. With the RWA there is
no temperature dependence in any case.Comment: 17 pages, 13 figures, v2 updated references, v3 clarified results and
corrected renormalization, v4 further clarified results and new Fig. 8-1
Coarse Grainings and Irreversibility in Quantum Field Theory
In this paper we are interested in the studying coarse-graining in field
theories using the language of quantum open systems. Motivated by the ideas of
Calzetta and Hu on correlation histories we employ the Zwanzig projection
technique to obtain evolution equations for relevant observables in
self-interacting scalar field theories. Our coarse-graining operation consists
in concentrating solely on the evolution of the correlation functions of degree
less than , a treatment which corresponds to the familiar from statistical
mechanics truncation of the BBKGY hierarchy at the n-th level. We derive the
equations governing the evolution of mean field and two-point functions thus
identifying the terms corresponding to dissipation and noise. We discuss
possible applications of our formalism, the emergence of classical behaviour
and the connection to the decoherent histories framework.Comment: 25 pages, Late
- …