14,554 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
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
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
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
Monte Carlo studies on the sensitivity of the HEGRA imaging atmospheric Cerenkov telescope system in observations of extended gamma-ray sources
In this paper, we present the results of Monte Carlo simulations of
atmospheric showers induced by diffuse gamma rays as detected by the
high-energy gamma ray astronomy (HEGRA) system of five imaging atmospheric
Cerenkov telescopes (IACTs). We have investigated the sensitivity of
observations on extended gamma ray emission over the entire field of view of
the instrument. We discuss a technique to search for extended gamma ray sources
within the field of view of the instrument. We give estimates for HEGRA
sensitivity of observations on extended TeV gamma ray sources.Comment: 21 pages, 7 figures, accepted for publication in "Journal of Physics
G: Nuclear and Particle Physics
Optimized phase switching using a single atom nonlinearity
We show that a nonlinear phase shift of pi can be obtained by using a single
two level atom in a one sided cavity with negligible losses. This result
implies that the use of a one sided cavity can significantly improve the pi/18
phase shift previously observed by Turchette et al. [Phys. Rev. Lett. 75, 4710
(1995)].Comment: 6 pages, 3 figures, added comments on derivation and assumption
Violation of Leggett-Garg inequalities in quantum measurements with variable resolution and back-action
Quantum mechanics violates Leggett-Garg inequalities because the operator
formalism predicts correlations between different spin components that would
correspond to negative joint probabilities for the outcomes of joint
measurements. However, the uncertainty principle ensures that such joint
measurements cannot be implemented without errors. In a sequential measurement
of the spin components, the resolution and back-action errors of the
intermediate measurement can be described by random spin flips acting on an
intrinsic joint probability. If the error rates are known, the intrinsic joint
probability can be reconstructed from the noisy statistics of the actual
measurement outcomes. In this paper, we use the spin-flip model of measurement
errors to analyze experimental data on photon polarization obtained with an
interferometric setup that allows us to vary the measurement strength and hence
the balance between resolution and back-action errors. We confirm that the
intrinsic joint probability obtained from the experimental data is independent
of measurement strength and show that the same violation of the Leggett-Garg
inequality can be obtained for any combination of measurement resolution and
back-action.Comment: 17 pages, 7 figure
Computing Web-scale Topic Models using an Asynchronous Parameter Server
Topic models such as Latent Dirichlet Allocation (LDA) have been widely used
in information retrieval for tasks ranging from smoothing and feedback methods
to tools for exploratory search and discovery. However, classical methods for
inferring topic models do not scale up to the massive size of today's publicly
available Web-scale data sets. The state-of-the-art approaches rely on custom
strategies, implementations and hardware to facilitate their asynchronous,
communication-intensive workloads.
We present APS-LDA, which integrates state-of-the-art topic modeling with
cluster computing frameworks such as Spark using a novel asynchronous parameter
server. Advantages of this integration include convenient usage of existing
data processing pipelines and eliminating the need for disk writes as data can
be kept in memory from start to finish. Our goal is not to outperform highly
customized implementations, but to propose a general high-performance topic
modeling framework that can easily be used in today's data processing
pipelines. We compare APS-LDA to the existing Spark LDA implementations and
show that our system can, on a 480-core cluster, process up to 135 times more
data and 10 times more topics without sacrificing model quality.Comment: To appear in SIGIR 201
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
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