151 research outputs found
Factorization of numbers with Gauss sums: II. Suggestions for implementations with chirped laser pulses
We propose three implementations of the Gauss sum factorization schemes
discussed in part I of this series: (i) a two-photon transition in a
multi-level ladder system induced by a chirped laser pulse, (ii) a chirped
one-photon transition in a two-level atom with a periodically modulated excited
state, and (iii) a linearly chirped one-photon transition driven by a sequence
of ultrashort pulses. For each of these quantum systems we show that the
excitation probability amplitude is given by an appropriate Gauss sum. We
provide rules how to encode the number N to be factored in our system and how
to identify the factors of N in the fluorescence signal of the excited state.Comment: 22 pages, 7 figure
Controlling Molecular Scattering by Laser-Induced Field-Free Alignment
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
preshaping 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. We provide
quantum and classical treatment of the deflection process. The effects of
strong deflecting field on the scattering of rotating molecules are considered
by the means of the adiabatic invariants formalism. This new control scheme
opens new ways for many applications involving molecular focusing, guiding and
trapping by optical and static fields
Squeezing of Atoms in a Pulsed Optical Lattice
We study the process of squeezing of an ensemble of cold atoms in a pulsed
optical lattice. The problem is treated both classically and
quantum-mechanically under various thermal conditions. We show that a dramatic
compression of the atomic density near the minima of the optical potential can
be achieved with a proper pulsing of the lattice. Several strategies leading to
the enhanced atomic squeezing are suggested, compared and optimized.Comment: Latex, 9 pages, 10 figures, submitted to PR
Orientation and Alignment Echoes
We present what is probably the simplest classical system featuring the echo
phenomenon - a collection of randomly oriented free rotors with dispersed
rotational velocities. Following excitation by a pair of time-delayed impulsive
kicks, the mean orientation/alignment of the ensemble exhibits multiple echoes
and fractional echoes. We elucidate the mechanism of the echo formation by
kick-induced filamentation of phase space, and provide the first experimental
demonstration of classical alignment echoes in a thermal gas of CO_2 molecules
excited by a pair of femtosecond laser pulses
Superrevivals in the quantum dynamics of a particle confined in a finite square well potential
We examine the revival features in wave packet dynamics of a particle
confined in a finite square well potential. The possibility of tunneling
modifies the revival pattern as compared to an infinite square well potential.
We study the dependence of the revival times on the depth of the square well
and predict the existence of superrevivals. The nature of these superrevivals
is compared with similar features seen in the dynamics of wavepackets in an
anharmonic oscillator potential.Comment: 8 pages in Latex two-column format with 5 figures (eps). To appear in
Physical Review
Echo in Optical Lattices: Stimulated Revival of Breathing Oscillations
We analyze a stimulated revival (echo) effect for the breathing modes of the
atomic oscillations in optical lattices. The effect arises from the dephasing
due to the weak anharmonicity being partly reversed in time by means of
additional parametric excitation of the optical lattice. The shape of the echo
response is obtained by numerically simulating the equation of motion for the
atoms with subsequent averaging over the thermal initial conditions. A
qualitative analysis of the phenomenon shows that the suggested echo mechanism
combines the features of both spin and phonon echoes.Comment: 13 pages, 3 figure
Quantum resonances in selective rotational excitation of molecules with a sequence of ultrashort laser pulses
We investigate experimentally the effect of quantum resonance in the
rotational excitation of the simplest quantum rotor - a diatomic molecule. By
using the techniques of high-resolution femtosecond pulse shaping and
rotational state-resolved detection, we measure directly the amount of energy
absorbed by molecules interacting with a periodic train of laser pulses, and
study its dependence on the train period. We show that the energy transfer is
significantly enhanced at quantum resonance, and use this effect for
demonstrating selective rotational excitation of two nitrogen isotopologues, and . Moreover, by tuning the period of the pulse train in
the vicinity of a fractional quantum resonance, we achieve spin-selective
rotational excitation of para- and ortho-isomers of .Comment: 5 pages, 4 figure
Fractional Echoes
We report the observation of fractional echoes in a double-pulse excited
nonlinear system. Unlike standard echoes which appear periodically at delays
which are integer multiple of the delay between the two exciting pulses, the
fractional echoes appear at rational fractions of this delay. We discuss the
mechanism leading to this phenomenon, and provide the first experimental
demonstration of fractional echoes by measuring third harmonic generation in a
thermal gas of CO2 molecules excited by a pair of femtosecond laser pulses
Extended Gaussian wave packet dynamics
We examine an extension to the theory of Gaussian wave packet dynamics in a
one-dimensional potential by means of a sequence of time dependent displacement
and squeezing transformations. Exact expressions for the quantum dynamics are
found, and relationships are explored between the squeezed system, Gaussian
wave packet dynamics, the time dependent harmonic oscillator, and wave packet
dynamics in a Gauss-Hermite basis. Expressions are given for the matrix
elements of the potential in some simple cases. Several examples are given,
including the propagation of a non-Gaussian initial state in a Morse potential
Coherent Manipulation of Quantum Delta-kicked Dynamics: Faster-than-classical Anomalous Diffusion
Large transporting regular islands are found in the classical phase space of
a modified kicked rotor system in which the kicking potential is reversed after
every two kicks. The corresponding quantum system, for a variety of system
parameters and over long time scales, is shown to display energy absorption
that is significantly faster than that associated with the underlying classical
anomalous diffusion. The results are of interest to both areas of quantum chaos
and quantum control.Comment: 6 pages, 4 figures, to appear in Physical Review
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