לוח שנה משולב

I present a synopsis of quantum phase-space propagation in
the Wigner representation, in the semiclassical regime, as a versatile
tool for the analysis of complex quantum dynamics. Two semiclassical
approximation schemes to the propagator of the Wigner function are
discussed, one based on van Vleck's semiclassical propagator, the
other on phase-space path integration. The former replaces the
Liouville propagator by a smooth quantum spot with an oscillatory
pattern reflecting the interference between pairs of non-identical
classical trajectories. The latter resolves sharp caustics in the
quantum spot in terms of Airy functions.
In the context of atomic and molecular dynamics, semiclassical Wigner propagation offers a natural initial-value representation. It is
applied to two prototypical nonlinear potentials, the Morse oscillator
and the quartic double well, and tested in a number of standard tasks
such as the computation of autocorrelation functions and the
propagation of coherent states. We find a good performance of the
semiclassical Wigner propagator even in the presence of marked quantum
effects, e.g., in coherent tunneling, and demonstate how
"sub-Planckian" oscillations are faithfully reproduced in the
propagation of Schroedinger cat states. Fresh results for a pair of
coupled Morse oscillators, with a partially chaotic dynamics, will be
presented as well. Options for an effective numerical implementation
of our method and for its integration in Monte-Carlo algorithms are
indicated.
As an important application of the semiclassical propagation of
quantum coherence, I will show that the diagonal Wigner propagator
is a suitable quantity to identify and resolve structures in
quantum-mechanical phase space that contribute to the spectral form
factor. They tend to localize on unstable periodic orbits of the
corresponding classical flow when the time argument coincides with the
respective period, hence can be interpreted as time-domain
scars. Consistency between the trace of the propagator and the form
factor implies the existence of additional non-classical features in
the diagonal propagator which are of the same order of magnitude as
the classical ones. As the propagator is not subject to the
uncertainty relation, these structures can be revealed with unlimited
(single pixel) resolution. I present numerical results for standard
models of quantum chaos which illustrate and confirm the theoretical
analysis.

Leveraging on detector technology currently used in synchrotron radiation tomography, we describe a novel microXCT capable of scanning sample sizes of several cm to mm dimensions with a variable resolution from mm to submicron resolution. The system overcomes the traditional disadvantage of conventional MicroCTs based on geometric magnification- where imaging resolution is limited to spot size of x-ray source, sample size and the sample-source distance. Furthermore, with the unique PhaseEnhanced detector, soft materials such as biological tissue, polymers, composites may be imaged with significantly higher contrast than traditional Flat Panel detectors. Small density variation in materials, such as mineral phases in geomaterials or fossils embedded within rocks may be imaged and be segmented for quantitative measurements. Characterization of porosity, particle shapes, cracks, defects, bonding thickness for porous composites, ceramics, fibers, geomaterials, tissue engineering and biological specimens will be presented. Results will be contrasted with those obtained from synchrotron, SEMs, histology and MRI.