18,982 research outputs found
Relativistic Quantum Information in Detectors-Field Interactions
We review Unruh-DeWitt detectors and other models of detector-field
interaction in a relativistic quantum field theory setting as a tool for
extracting detector-detector, field-field and detector-field correlation
functions of interest in quantum information science, from entanglement
dynamics to quantum teleportation. We in particular highlight the contrast
between the results obtained from linear perturbation theory which can be
justified provided switching effects are properly accounted for, and the
nonperturbative effects from available analytic expressions which incorporate
the backreaction effects of the quantum field on the detector behaviour.Comment: 21 pages, 3 figures. Prepared for the special focus issue on RQ
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
Then again, how often does the Unruh-DeWitt detector click if we switch it carefully?
The transition probability in first-order perturbation theory for an
Unruh-DeWitt detector coupled to a massless scalar field in Minkowski space is
calculated. It has been shown recently that the conventional
regularisation prescription for the correlation function leads to non-Lorentz
invariant results for the transition rate, and a different regularisation,
involving spatial smearing of the field, has been advocated to replace it. We
show that the non-Lorentz invariance arises solely from the assumption of
sudden switch-on and switch-off of the detector, and that when the model
includes a smooth switching function the results from the conventional
regularisation are both finite and Lorentz invariant. The sharp switching limit
of the model is also discussed, as well as the falloff properties of the
spectrum for large frequencies.Comment: 16 pages, v3. Final published version with section 5 expande
New Insights into Uniformly Accelerated Detector in a Quantum Field
We obtained an exact solution for a uniformly accelerated Unruh-DeWitt
detector interacting with a massless scalar field in (3+1) dimensions which
enables us to study the entire evolution of the total system, from the initial
transient to late-time steady state. We find that the Unruh effect as derived
from time-dependent perturbation theory is valid only in the transient stage
and is totally invalid for cases with proper acceleration smaller than the
damping constant. We also found that, unlike in (1+1)D results, the (3+1)D
uniformly accelerated Unruh-DeWitt detector in a steady state does emit a
positive radiated power of quantum nature at late-times, but it is not
connected to the thermal radiance experienced by the detector in the Unruh
effect proper.Comment: 6 pages, invited talk given by SYL at the conference of International
Association for Relativistic Dynamics (IARD), June 2006, Storrs, Connecticut,
US
Spin Transport in Two Dimensional Hopping Systems
A two dimensional hopping system with Rashba spin-orbit interaction is
considered. Our main interest is concerned with the evolution of the spin
degree of freedom of the electrons. We derive the rate equations governing the
evolution of the charge density and spin polarization of this system in the
Markovian limit in one-particle approximation. If only two-site hopping events
are taken into account, the evolution of the charge density and of the spin
polarization is found to be decoupled. A critical electric field is found,
above which oscillations are superimposed on the temporal decay of the total
polarization. A coupling between charge density and spin polarization occurs on
the level of three-site hopping events. The coupling terms are identified as
the anomalous Hall effect and the recently proposed spin Hall effect. Thus, an
unpolarized charge current through a sheet of finite width leads to a
transversal spin accumulation in our model system.Comment: 15 pages, 3 figure
Mott versus Slater-type metal-insulator transition in Mn-substituted Sr3Ru2O7
We present a temperature-dependent x-ray absorption (XAS) and resonant
elastic x-ray scattering (REXS) study of the metal-insulator transition (MIT)
in Sr3(Ru1-xMnx)2O7. The XAS results reveal that the MIT drives the onset of
local antiferromagnetic correlations around the Mn impurities, a precursor of
the long-range antiferromagnetism detected by REXS at T_order<T_MIT. This
establishes that the MIT is of the Mott-type (electronic correlations) as
opposed to Slater-type (magnetic order). While this behavior is induced by Mn
impurities, the (1/4,1/4,0) order exists for a wide range of Mn concentrations,
and points to an inherent instability of the parent compound.Comment: In press. A high-resolution version can be found at
http://www.phas.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Articles/MnSRO_REXS.pd
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