16,022 research outputs found
Scaled Spectroscopy of 1Se and 1Po Highly Excited States of Helium
In this paper, we examine the properties of the 1Se and 1Po states of helium,
combining perimetric coordinates and complex rotation methods. We compute
Fourier transforms of quantities of physical interest, among them the average
of the operator cos(theta_12), which measures the correlation between the two
electrons. Graphs obtained for both 1Se and 1Po states show peaks at action of
classical periodic orbits, either "frozen planet" orbit or asymmetric stretch
orbits. This observation legitimates the semiclassical quantization of helium
with those orbits only, not just for S states but also for P states, which is a
new result. To emphasize the similarity between the S and P states we show
wavefunctions of 1Po states, presenting the same structure as 1Se states,
namely the "frozen planet" and asymmetric stretch configurations.Comment: revtex 15 pages with 6 figures, 2 figures (large) are available on
request at email address [email protected]. to appear in J. Phys. B
(April 98
Measuring Multi-Configurational Character by Orbital Entanglement
One of the most critical tasks at the very beginning of a quantum chemical
investigation is the choice of either a multi- or single-configurational
method. Naturally, many proposals exist to define a suitable diagnostic of the
multi-configurational character for various types of wave functions in order to
assist this crucial decision. Here, we present a new orbital-entanglement based
multi-configurational diagnostic termed . The correspondence of
orbital entanglement and static (or nondynamic) electron correlation permits
the definition of such a diagnostic. We chose our diagnostic to meet important
requirements such as well-defined limits for pure single-configurational and
multi-configurational wave functions. The diagnostic can be
evaluated from a partially converged, but qualitatively correct, and therefore
inexpensive density matrix renormalization group wave function as in our
recently presented automated active orbital selection protocol. Its robustness
and the fact that it can be evaluated at low cost make this diagnostic a
practical tool for routine applications.Comment: 8 pages, 2 figure, 3 table
Control of quantum phenomena: Past, present, and future
Quantum control is concerned with active manipulation of physical and
chemical processes on the atomic and molecular scale. This work presents a
perspective of progress in the field of control over quantum phenomena, tracing
the evolution of theoretical concepts and experimental methods from early
developments to the most recent advances. The current experimental successes
would be impossible without the development of intense femtosecond laser
sources and pulse shapers. The two most critical theoretical insights were (1)
realizing that ultrafast atomic and molecular dynamics can be controlled via
manipulation of quantum interferences and (2) understanding that optimally
shaped ultrafast laser pulses are the most effective means for producing the
desired quantum interference patterns in the controlled system. Finally, these
theoretical and experimental advances were brought together by the crucial
concept of adaptive feedback control, which is a laboratory procedure employing
measurement-driven, closed-loop optimization to identify the best shapes of
femtosecond laser control pulses for steering quantum dynamics towards the
desired objective. Optimization in adaptive feedback control experiments is
guided by a learning algorithm, with stochastic methods proving to be
especially effective. Adaptive feedback control of quantum phenomena has found
numerous applications in many areas of the physical and chemical sciences, and
this paper reviews the extensive experiments. Other subjects discussed include
quantum optimal control theory, quantum control landscapes, the role of
theoretical control designs in experimental realizations, and real-time quantum
feedback control. The paper concludes with a prospective of open research
directions that are likely to attract significant attention in the future.Comment: Review article, final version (significantly updated), 76 pages,
accepted for publication in New J. Phys. (Focus issue: Quantum control
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