419 research outputs found
New bases for a general definition for the moving preferred basis
One of the challenges of the Environment-Induced Decoherence (EID) approach
is to provide a simple general definition of the moving pointer basis or moving
preferred basis. In this letter we prove that the study of the poles that
produce the decaying modes in non-unitary evolution, could yield a general
definition of the relaxation, the decoherence times, and the moving preferred
basis. These probably are the most important concepts in the theory of
decoherence, one of the most relevant chapters of theoretical (and also
practical) quantum mechanics. As an example we solved the Omnes (or
Lee-Friedrich) model using our theory.Comment: 6 page
Quantum oscillations and black hole ringing
We show that strongly coupled field theories with holographic gravity duals
at finite charge density and low temperatures can undergo de Haas - van Alphen
quantum oscillations as a function of an external magnetic field. Exhibiting
this effect requires computation of the one loop contribution of charged bulk
fermions to the free energy. The one loop calculation is performed using a
formula expressing determinants in black hole backgrounds as sums over
quasinormal modes. At zero temperature, the periodic nonanalyticities in the
magnetic susceptibility as a function of the inverse magnetic field depend on
the low energy scaling behavior of fermionic operators in the field theory, and
are found to be softer than in weakly coupled theories. We also obtain
numerical and WKB results for the quasinormal modes of charged bosons in dyonic
black hole backgrounds, finding evidence for nontrivial periodic behavior as a
function of the magnetic field.Comment: 1+53 pages. 9 figures. v2: important changes to sections 3.4 - 3.6.
contribution of branch cut poles include
Can Gravity Distinguish Between Dirac and Majorana Neutrinos?
We show that spin-gravity interaction can distinguish between Dirac and
Majorana neutrino wave packets propagating in a Lense-Thirring background.
Using time-independent perturbation theory and gravitational phase to generate
a perturbation Hamiltonian with spin-gravity coupling, we show that the
associated matrix element for the Majorana neutrino differs significantly from
its Dirac counterpart. This difference can be demonstrated through significant
gravitational corrections to the neutrino oscillation length for a two-flavour
system, as shown explicitly for SN1987A.Comment: 4 pages, 2 figures; minor changes of text; typo corrected; accepted
in Physical Review Letter
The Quantum Mechanics of Hyperion
This paper is motivated by the suggestion [W. Zurek, Physica Scripta, T76,
186 (1998)] that the chaotic tumbling of the satellite Hyperion would become
non-classical within 20 years, but for the effects of environmental
decoherence. The dynamics of quantum and classical probability distributions
are compared for a satellite rotating perpendicular to its orbital plane,
driven by the gravitational gradient. The model is studied with and without
environmental decoherence. Without decoherence, the maximum quantum-classical
(QC) differences in its average angular momentum scale as hbar^{2/3} for
chaotic states, and as hbar^2 for non-chaotic states, leading to negligible QC
differences for a macroscopic object like Hyperion. The quantum probability
distributions do not approach their classical limit smoothly, having an
extremely fine oscillatory structure superimposed on the smooth classical
background. For a macroscopic object, this oscillatory structure is too fine to
be resolved by any realistic measurement. Either a small amount of smoothing
(due to the finite resolution of the apparatus) or a very small amount of
environmental decoherence is sufficient ensure the classical limit. Under
decoherence, the QC differences in the probability distributions scale as
(hbar^2/D)^{1/6}, where D is the momentum diffusion parameter. We conclude that
decoherence is not essential to explain the classical behavior of macroscopic
bodies.Comment: 17 pages, 24 figure
EPR before EPR: a 1930 Einstein-Bohr thought experiment revisited
In 1930 Einstein argued against consistency of the time-energy uncertainty
relation by discussing a thought experiment involving a measurement of mass of
the box which emitted a photon. Bohr seemingly triumphed over Einstein by
arguing that the Einstein's own general theory of relativity saves the
consistency of quantum mechanics. We revisit this thought experiment from a
modern point of view at a level suitable for undergraduate readership and find
that neither Einstein nor Bohr was right. Instead, this thought experiment
should be thought of as an early example of a system demonstrating nonlocal
"EPR" quantum correlations, five years before the famous
Einstein-Podolsky-Rosen paper.Comment: 11 pages, revised, accepted for publication in Eur. J. Phy
Quantum erasure within the Optical Stern-Gerlach Model
In the optical Stern-Gerlach effect the two branches in which the incoming
atomic packet splits up can display interference pattern outside the cavity
when a field measurement is made which erases the which-way information on the
quantum paths the system can follow. On the contrary, the mere possibility to
acquire this information causes a decoherence effect which cancels out the
interference pattern. A phase space analysis is also carried out to investigate
on the negativity of the Wigner function and on the connection between its
covariance matrix and the distinguishability of the quantum paths.Comment: 7 pages, 3 figure
Destruction of states in quantum mechanics
A description of destruction of states on the grounds of quantum mechanics
rather than quantum field theory is proposed. Several kinds of maps called
supertraces are defined and used to describe the destruction procedure. The
introduced algorithm can be treated as a supplement to the von Neumann-Lueders
measurement. The discussed formalism may be helpful in a description of EPR
type experiments and in quantum information theory.Comment: 14 pp, 1 eps figure, LaTeX2e using iopart class. Final version, will
be published in J. Phys. A: Math. Ge
Extended Representations of Observables and States for a Noncontextual Reinterpretation of QM
A crucial and problematical feature of quantum mechanics (QM) is
nonobjectivity of properties. The ESR model restores objectivity reinterpreting
quantum probabilities as conditional on detection and embodying the
mathematical formalism of QM into a broader noncontextual (hence local)
framework. We propose here an improved presentation of the ESR model containing
a more complete mathematical representation of the basic entities of the model.
We also extend the model to mixtures showing that the mathematical
representations of proper mixtures does not coincide with the mathematical
representation of mixtures provided by QM, while the representation of improper
mixtures does. This feature of the ESR model entails that some interpretative
problems raising in QM when dealing with mixtures are avoided. From an
empirical point of view the predictions of the ESR model depend on some
parameters which may be such that they are very close to the predictions of QM
in most cases. But the nonstandard representation of proper mixtures allows us
to propose the scheme of an experiment that could check whether the predictions
of QM or the predictions of the ESR model are correct.Comment: 17 pages, standard latex. Extensively revised versio
Archaeological Geophysical Prospection in Peatland Environments: case studies and suggestions for future practice
Peatland environments, in contrast to ‘dry-land’ sites, preserve organic material, including anthropogenic objects, because they are anaerobic, and are therefore of great importance to archaeology. Peat also preserves macro- and micro- paleoenvironmental evidence and is the primary resource for understanding past climates and ecology. Archaeological sites often lie within or at the base of wet, deep, homogenous peat rendering them invisible to surface observers. As a result, they most often c..
Optimal Monitoring of Position in Nonlinear Quantum Systems
We discuss a model of repeated measurements of position in a quantum system
which is monitored for a finite amount of time with a finite instrumental
error. In this framework we recover the optimum monitoring of a harmonic
oscillator proposed in the case of an instantaneous collapse of the
wavefunction into an infinite-accuracy measurement result. We also establish
numerically the existence of an optimal measurement strategy in the case of a
nonlinear system. This optimal strategy is completely defined by the spectral
properties of the nonlinear system.Comment: 4 pages, REVTeX 3.0, 4 PostScript figure
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