1,441 research outputs found
Adiabatic theorem for non-hermitian time-dependent open systems
In the conventional quantum mechanics (i.e., hermitian QM) the adia- batic
theorem for systems subjected to time periodic fields holds only for bound
systems and not for open ones (where ionization and dissociation take place)
[D. W. Hone, R. Ketzmerik, and W. Kohn, Phys. Rev. A 56, 4045 (1997)]. Here
with the help of the (t,t') formalism combined with the complex scaling method
we derive an adiabatic theorem for open systems and provide an analytical
criteria for the validity of the adiabatic limit. The use of the complex
scaling transformation plays a key role in our derivation. As a numerical
example we apply the adiabatic theorem we derived to a 1D model Hamiltonian of
Xe atom which interacts with strong, monochromatic sine-square laser pulses. We
show that the gener- ation of odd-order harmonics and the absence of
hyper-Raman lines, even when the pulses are extremely short, can be explained
with the help of the adiabatic theorem we derived
Theory of diatomic molecules in an external electromagnetic field from first quantum mechanical principles
We study a general problem of the
translational/rotational/vibrational/electronic dynamics of a diatomic molecule
exposed to an interaction with an arbitrary external electromagnetic field. The
theory developed in this paper is relevant to a variety of specific
applications. Such as, alignment or orientation of molecules by lasers,
trapping of ultracold molecules in optical traps, molecular optics and
interferometry, rovibrational spectroscopy of molecules in the presence of
intense laser light, or generation of high order harmonics from molecules.
Starting from the first quantum mechanical principles, we derive an appropriate
molecular Hamiltonian suitable for description of the center of mass,
rotational, vibrational and electronic molecular motions driven by the field
within the electric dipole approximation. Consequently, the concept of the
Born-Oppenheimer separation between the electronic and the nuclear degrees of
freedom in the presence of an electromagnetic field is introduced. Special
cases of the dc/ac field limits are then discussed separately. Finally, we
consider a perturbative regime of a weak dc/ac field, and obtain simple
analytic formulas for the associated Born-Oppenheimer
translational/rotational/vibrational molecular Hamiltonian
Amplification of High Harmonics Using Weak Perturbative High Frequency Radiation
The mechanism underlying the substantial amplification of the high-order
harmonics q \pm 2K (K integer) upon the addition of a weak seed XUV field of
harmonic frequency q\omega to a strong IR field of frequency \omega is analyzed
in the framework of the quantum-mechanical Floquet formalism and the
semiclassical re-collision model. According to the Floquet analysis, the
high-frequency field induces transitions between several Floquet states and
leads to the appearance of new dipole cross terms. The semiclassical
re-collision model suggests that the origin of the enhancement lies in the
time-dependent modulation of the ground electronic state induced by the XUV
field.Comment: 8 pages, 2 figure
A global biogeocenotical biosphere simulation
This model of the D. Forrester type, constructed in differential equations, predicts the food and mineral supply for the factors biosphere population, depending on two socio-economic factors, until about the year 2500. If contemporary rates of natural resources utilization are maintained and there is no management of the environment, food resources will begin to limit human population growth after 2200, and mineral resources will after 2300. A decrease in the biosphere pollution, increase in effective agricultural production, and discovery of new energy sources may forestall or completely avert the onset of a crisis situation. Conservation measures, according to the model, are to a considerable extent realizable only if carried out simultaneously in both areas
Strong impact of light induced conical intersections on the spectrum of diatomic molecules
We show that dressing of diatomic molecules by running laser waves gives rise
to conical intersections (CIs). Due to presence of such CIs, the rovibronic
molecular motions are strongly coupled. A pronounced impact of the CI on the
spectrum of molecule is demonstrated via numerical calculation for weak
and moderate laser intensity, and an experiment is suggested on this basis. The
position of the light induced CI and the strength of its non-adiabatic
couplings can be chosen by changing the frequency and intensity of the used
running laser wave. This offers new possibilities to control the photo-induced
rovibronic molecular dynamics.Comment: 4 pages, 7 figure
Breakdown of adiabatic transfer of light in waveguides in the presence of absorption
In atomic physics, adiabatic evolution is often used to achieve a robust and
efficient population transfer. Many adiabatic schemes have also been
implemented in optical waveguide structures. Recently there has been increasing
interests in the influence of decay and absorption, and their engineering
applications. Here it is shown that even a small decay can significantly
influence the dynamical behaviour of a system, above and beyond a mere change
of the overall norm. In particular, a small decay can lead to a breakdown of
adiabatic transfer schemes, even when both the spectrum and the eigenfunctions
are only sightly modified. This is demonstrated for the generalization of a
STIRAP scheme that has recently been implemented in optical waveguide
structures. Here the question how an additional absorption in either the
initial or the target waveguide influences the transfer property of the scheme
is addressed. It is found that the scheme breaks down for small values of the
absorption at a relatively sharp threshold, which can be estimated by simple
analytical arguments.Comment: 8 pages, 7 figures, revised and extende
Entanglement and spin squeezing in non-Hermitian phase transitions
We show that non-Hermitian dynamics generate substantial entanglement in
many-body systems. We consider the non-Hermitian Lipkin-Meshkov-Glick model and
show that its phase transition occurs with maximum multiparticle entanglement:
there is full N-particle entanglement at the transition, in contrast to the
Hermitian case. The non-Hermitian model also exhibits more spin squeezing than
the Hermitian model, showing that non-Hermitian dynamics are useful for quantum
metrology. Experimental implementations with trapped ions and cavity QED are
discussed.Comment: 5 pages + appendi
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