Recent measurements of resonance widths for low-energy neutron scattering off
heavy nuclei show large deviations from the standard Porter-Thomas
distribution. We propose a new resonance width distribution based on the random
matrix theory for an open quantum system. Two methods of derivation lead to a
single analytical expression; in the limit of vanishing continuum coupling, we
recover the Porter-Thomas distribution. The result depends on the ratio of
typical widths $\Gamma$ to the energy level spacing $D$ via the dimensionless
parameter $\kappa=(\pi\Gamma/2D)$. The new distribution suppresses small widths
and increases the probabilities of larger widths.Comment: 8 pages, 2 figure
We uncover signatures of quantum chaos in the many-body dynamics of a Bose-Einstein condensate-based quantum ratchet in a toroidal trap. We propose measures including entanglement, condensate depletion, and spreading over a fixed basis in many-body Hilbert space, which quantitatively identify the region in which quantum chaotic many-body dynamics occurs, where random matrix theory is limited or inaccessible. With these tools, we show that many-body quantum chaos is neither highly entangled nor delocalized in the Hilbert space, contrary to conventionally expected signatures of quantum chaos.
We report an analytic solution for a three--level atom driven by arbitrary
time-dependent electromagnetic pulses. In particular, we consider far--detuned
driving pulses and show an excellent match between our analytic result and the
numerical simulations. We use our solution to derive a pulse area theorem for
three--level $V$ and $\Lambda$ systems without making the rotating wave
approximation. Formulated as an energy conservation law, this pulse area
theorem provides a simple picture for a pulse propagation through a
three--level media
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