97 research outputs found
Controlling Quantum Rotation With Light
Semiclassical catastrophes in the dynamics of a quantum rotor (molecule)
driven by a strong time-varying field are considered. We show that for strong
enough fields, a sharp peak in the rotor angular distribution can be achieved
via time-domain focusing phenomenon, followed by the formation of angular
rainbows and glory-like angular structures. Several scenarios leading to the
enhanced angular squeezing are proposed that use specially designed and
optimized sequences of pulses. The predicted effects can be observed in many
processes, ranging from molecular alignment (orientation) by laser fields to
heavy-ion collisions, and the squeezing of cold atoms in a pulsed optical
lattice.Comment: 8 pages, Latex, 8 figures, based on the talk given at the Eighth
Rochester Conference on Coherence and Quantum Optics (June 13-16, 2001). To
appear in the proceedings of CQO8 (Plenum, 2002
Revivals, classical periodicity, and zitterbewegung of electron currents in monolayer graphene
Revivals of electric current in graphene in the presence of an external
magnetic field are described. It is shown that when the electrons are prepared
in the form of wave packets assuming a Gaussian population of only positive (or
negative) energy Landau levels, the presence of the magnetic field induce
revivals of the electron currents, besides the classical cyclotron motion. When
the population comprises both positive and negative energy Landau levels,
revivals of the electric current manifest simultaneously with zitterbewegung
and the classical cyclotron motion. We relate the temporal scales of these
three effects and discuss to what extent these results hold for real graphene
samples
Atom Lithography with Near-Resonant Light Masks: Quantum Optimization Analysis
We study the optimal focusing of two-level atoms with a near resonant
standing wave light, using both classical and quantum treatments of the
problem. Operation of the focusing setup is considered as a nonlinear spatial
squeezing of atoms in the thin- and thick-lens regimes. It is found that the
near-resonant standing wave focuses the atoms with a reduced background in
comparison with far-detuned light fields. For some parameters, the quantum
atomic distribution shows even better localization than the classical one.
Spontaneous emission effects are included via the technique of quantum Monte
Carlo wave function simulations. We investigate the extent to which
non-adiabatic and spontaneous emission effects limit the achievable minimal
size of the deposited structures.Comment: 10 pages including 11 figures in Revte
Deflection of Rotating Symmetric Molecules by Inhomogeneous Fields
We consider deflection of rotating symmetric molecules by inhomogeneous
optical and static electric fields, compare results with the case of linear
molecules, and find new singularities in the distribution of the scattering
angle. Scattering of the prolate/oblate molecules is analyzed in detail, and it
is shown that the process can be efficiently controlled by means of short and
strong femtosecond laser pulses. In particular, the angular dispersion of the
deflected molecules may be dramatically reduced by laser-induced molecular
pre-alignment. We first study the problem by using a simple classical model,
and then find similar results by means of more sophisticated methods, including
the formalism of adiabatic invariants and direct numerical simulation of the
Euler-Lagrange equations of motion. The suggested control scheme opens new ways
for many applications involving molecular focusing, guiding, and trapping by
optical and static fields
Deflection of field-free aligned molecules
We consider deflection of polarizable molecules by inhomogeneous optical
fields, and analyze the role of molecular orientation and rotation in the
scattering process. It is shown that molecular rotation induces spectacular
rainbow-like features in the distribution of the scattering angle. Moreover, by
pre-shaping molecular angular distribution with the help of short and strong
femtosecond laser pulses, one may efficiently control the scattering process,
manipulate the average deflection angle and its distribution, and reduce
substantially the angular dispersion of the deflected molecules. This opens new
ways for many applications involving molecular focusing, guiding and trapping
by optical and static fields.Comment: 4 pages, 4 figure
Wave packet revivals in a graphene quantum dot in a perpendicular magnetic field
We study the time-evolution of localized wavepackets in graphene quantum dots
under a perpendicular magnetic field, focusing on the quasiclassical and
revival periodicities, for different values of the magnetic field intensities
in a theoretical framework. We have considered contributions of the two
inequivalent points in the Brillouin zone. The revival time has been found as
an observable that shows the break valley degeneracy.Comment: 5 pages, 4 figures, corrected typo, To appear in Phys. Rev.
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