14 research outputs found
Coherent spatial control of wave packet dynamics on quantum lattices
Quantum lattices are pivotal in the burgeoning fields of quantum materials
and information science. Rapid developments in microscopy and quantum
engineering allow for preparing and monitoring wave-packet dynamics on quantum
lattices with increasing spatial and temporal resolution. Motivated by these
emerging research interests, we present an analytical study of wave packet
diffusivity and diffusion length on tight-binding quantum lattices subject to
stochastic noise. Our analysis points to the crucial role of spatial coherence
and predicts a set of novel phenomena: noise can enhance the transient
diffusivity and diffusion length of sufficiently extended initial states; A
smooth Gaussian initial state spreads slower than a localized initial state; A
standing or traveling initial state with large momentum spreads faster than a
localized initial state and exhibits a noise-induced peak in the transient
diffusivity; The change in the time-dependent diffusivity and diffusion length
relative to a localized initial state follows a universal dependence on the
Gaussian width. These theoretical predictions and the underlying mechanism of
spatial coherence suggest the possibility of controlling the wave packet
dynamics on quantum lattices by spatial manipulations, which will have
implications for materials science and quantum technologies.Comment: 8 pages, 5 figure
Long-Lasting Orientation of Symmetric-top Molecules Excited by Two-Color Femtosecond Pulses
Impulsive orientation of symmetric-top molecules excited by two-color
femtosecond pulses is considered. In addition to the well-known transient
orientation appearing immediately after the pulse and then reemerging
periodically due to quantum revivals, we report the phenomenon of field-free
long-lasting orientation. Long-lasting means that the time averaged orientation
remains non-zero until destroyed by other physical effects, e.g. intermolecular
collisions. The effect is caused by the combined action of the
field-polarizability and field-hyperpolarizability interactions. The dependence
of degree of long-lasting orientation on temperature and pulse's parameters is
considered. The effect can be measured by means of second (or higher-order)
harmonic generation, and may be used to control the deflection of molecules
traveling through inhomogeneous electrostatic fields.Comment: 12 pages, 7 figure
Enhanced persistent orientation of asymmetric-top molecules induced by cross-polarized terahertz pulses
We investigate the persistent orientation of asymmetric-top molecules induced by time-delayed THz pulses that are either collinearly or cross polarized. Our theoretical and numerical results demonstrate that the orthogonal configuration outperforms the collinear one, and a significant degree of persistent orientation—approximately 10% at 5 K and nearly 3% at room temperature—may be achieved through parameter optimization. The dependence of the persistent orientation factor on temperature and field parameters is studied in detail. The proposed application of two orthogonally polarized THz pulses is both practical and efficient. Its applicability under standard laboratory conditions lays a solid foundation for future experimental realization of THz-induced persistent molecular orientation
Visualizing coherent molecular rotation in a gaseous medium
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