17,250 research outputs found
Simulation of interaction Hamiltonians by quantum feedback: a comment on the dynamics of information exchange between coupled systems
Since quantum feedback is based on classically accessible measurement
results, it can provide fundamental insights into the dynamics of quantum
systems by making available classical information on the evolution of system
properties and on the conditional forces acting on the system. In this paper,
the feedback-induced interaction dynamics between a pair of quantum systems is
analyzed. It is pointed out that any interaction Hamiltonian can be simulated
by local feedback if the levels of decoherence are sufficiently high. The
boundary between genuine entanglement generating quantum interactions and
non-entangling classical interactions is identified and the nature of the
information exchange between two quantum systems during an interaction is
discussed.Comment: 14 pages, 4 figures; invited paper for the special issue of J. Opt. B
on quantum contro
Mean first passage time for fission potentials having structure
A schematic model of over-damped motion is presented which permits one to
calculate the mean first passage time for nuclear fission. Its asymptotic value
may exceed considerably the lifetime suggested by Kramers rate formula, which
applies only to very special, favorable potentials and temperatures. The
additional time obtained in the more general case is seen to allow for a
considerable increment in the emission of light particles.Comment: 7 pages, LaTex, 7 postscript figures; Keywords: Decay rate, mean
first passage tim
Time scales for fission at finite temperature
The concept of the "transient effect" is examined in respect of a "mean first
passage time". It is demonstrated that the time the fissioning system stays
inside the barrier is much larger than suggested by the transient time, and
that no enhancement of emission of neutrons over that given by Kramers' rate
formula ought to be considered.Comment: 6 pages, LaTex, 3 postscript figures; Keywords: Decay rate, transient
effect, mean first passage time; "Symposium on Nuclear Clusters",
Rauischholzhausen, Germany, 5-9 August 200
Statistical fluctuations for the fission process on its decent from saddle to scission
We reconsider the importance of statistical fluctuations for fission dynamics
beyond the saddle in the light of recent evaluations of transport coefficients
for average motion. The size of these fluctuations are estimated by means of
the Kramers-Ingold solution for the inverted oscillator, which allows for an
inclusion of quantum effects.Comment: 12 pages, Latex, 5 Postscript figures; submitted to PRC e-mail:
[email protected] www home page:
http://www.physik.tu-muenchen.de/tumphy/e/T36/hofmann.htm
Pro-Lie Groups: A survey with Open Problems
A topological group is called a pro-Lie group if it is isomorphic to a closed
subgroup of a product of finite-dimensional real Lie groups. This class of
groups is closed under the formation of arbitrary products and closed subgroups
and forms a complete category. It includes each finite-dimensional Lie group,
each locally compact group which has a compact quotient group modulo its
identity component and thus, in particular, each compact and each connected
locally compact group; it also includes all locally compact abelian groups.
This paper provides an overview of the structure theory and Lie theory of
pro-Lie groups including results more recent than those in the authors'
reference book on pro-Lie groups. Significantly, it also includes a review of
the recent insight that weakly complete unital algebras provide a natural
habitat for both pro-Lie algebras and pro-Lie groups, indeed for the
exponential function which links the two. (A topological vector space is weakly
complete if it is isomorphic to a power of an arbitrary set of copies of
. This class of real vector spaces is at the basis of the Lie theory of
pro-Lie groups.) The article also lists 12 open questions connected with
pro-Lie groups.Comment: 19 page
Complex joint probabilities as expressions of determinism in quantum mechanics
The density operator of a quantum state can be represented as a complex joint
probability of any two observables whose eigenstates have non-zero mutual
overlap. Transformations to a new basis set are then expressed in terms of
complex conditional probabilities that describe the fundamental relation
between precise statements about the three different observables. Since such
transformations merely change the representation of the quantum state, these
conditional probabilities provide a state-independent definition of the
deterministic relation between the outcomes of different quantum measurements.
In this paper, it is shown how classical reality emerges as an approximation to
the fundamental laws of quantum determinism expressed by complex conditional
probabilities. The quantum mechanical origin of phase spaces and trajectories
is identified and implications for the interpretation of quantum measurements
are considered. It is argued that the transformation laws of quantum
determinism provide a fundamental description of the measurement dependence of
empirical reality.Comment: 12 pages, including 1 figure, updated introduction includes
references to the historical background of complex joint probabilities and to
related work by Lars M. Johanse
Mean first passage time for nuclear fission and the emission of light particles
The concept of a mean first passage time is used to study the time lapse over
which a fissioning system may emit light particles. The influence of the
"transient" and "saddle to scission times" on this emission are critically
examined. It is argued that within the limits of Kramers' picture of fission no
enhancement over that given by his rate formula need to be considered.Comment: 4 pages, RevTex, 4 postscript figures; with correction of misprints;
appeared in Phys. Rev. Lett.90.13270
Finite resolution measurement of the non-classical polarization statistics of entangled photon pairs
By limiting the resolution of quantum measurements, the measurement induced
changes of the quantum state can be reduced, permitting subsequent measurements
of variables that do not commute with the initially measured property. It is
then possible to experimentally determine correlations between non-commuting
variables. The application of this method to the polarization statistics of
entangled photon pairs reveals that negative conditional probabilities between
non-orthogonal polarization components are responsible for the violation of
Bell's inequalities. Such negative probabilities can also be observed in finite
resolution measurements of the polarization of a single photon. The violation
of Bell's inequalities therefore originates from local properties of the
quantum statistics of single photon polarization.Comment: 15 pages, 5 figures and 1 table, new figure to illustrate results,
improved explanation of statistical analysi
Nuclear fission: The "onset of dissipation" from a microscopic point of view
Semi-analytical expressions are suggested for the temperature dependence of
those combinations of transport coefficients which govern the fission process.
This is based on experience with numerical calculations within the linear
response approach and the locally harmonic approximation. A reduced version of
the latter is seen to comply with Kramers' simplified picture of fission. It is
argued that for variable inertia his formula has to be generalized, as already
required by the need that for overdamped motion the inertia must not appear at
all. This situation may already occur above T=2 MeV, where the rate is
determined by the Smoluchowski equation. Consequently, comparison with
experimental results do not give information on the effective damping rate, as
often claimed, but on a special combination of local stiffnesses and the
friction coefficient calculated at the barrier.Comment: 31 pages, LaTex, 9 postscript figures; final, more concise version,
accepted for publication in PRC, with new arguments about the T-dependence of
the inertia; e-mail: [email protected]
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