2,776 research outputs found
Extension of the Morris-Shore transformation to multilevel ladders
We describe situations in which chains of N degenerate quantum energy levels,
coupled by time-dependent external fields, can be replaced by independent sets
of chains of length N, N-1,...,2 and sets of uncoupled single states. The
transformation is a generalization of the two-level Morris-Shore transformation
[J.R. Morris and B.W. Shore, Phys. Rev. A 27, 906 (1983)]. We illustrate the
procedure with examples of three-level chains
Stimulated Raman adiabatic passage analogs in classical physics
Stimulated Raman adiabatic passage (STIRAP) is a well established technique
for producing coherent population transfer in a three-state quantum system. We
here exploit the resemblance between the Schrodinger equation for such a
quantum system and the Newton equation of motion for a classical system
undergoing torque to discuss several classical analogs of STIRAP, notably the
motion of a moving charged particle subject to the Lorentz force of a
quasistatic magnetic field, the orientation of a magnetic moment in a slowly
varying magnetic field, the Coriolis effect and the inertial frame dragging
effect. Like STIRAP, those phenomena occur for counterintuitively ordered field
pulses and are robustly insensitive to small changes in the interaction
properties
An optimality criterion for sizing members of heated structures with temperature constraints
A thermal optimality criterion is presented for sizing members of heated structures with multiple temperature constraints. The optimality criterion is similar to an existing optimality criterion for design of mechanically loaded structures with displacement constraints. Effectiveness of the thermal optimality criterion is assessed by applying it to one- and two-dimensional thermal problems where temperatures can be controlled by varying the material distribution in the structure. Results obtained from the optimality criterion agree within 2 percent with results from a closed-form solution and with results from a mathematical programming technique. The thermal optimality criterion augments existing optimality criteria for strength and stiffness related constraints and offers the possibility of extension of optimality techniques to sizing structures with combined thermal and mechanical loading
Measuring a coherent superposition
We propose a simple method for measuring the populations and the relative
phase in a coherent superposition of two atomic states. The method is based on
coupling the two states to a third common (excited) state by means of two laser
pulses, and measuring the total fluorescence from the third state for several
choices of the excitation pulses.Comment: 7 pages, 1 figure, twocolumn REVTe
Phase shifts in nonresonant coherent excitation
Far-off-resonant pulsed laser fields produce negligible excitation between
two atomic states but may induce considerable phase shifts. The acquired phases
are usually calculated by using the adiabatic-elimination approximation. We
analyze the accuracy of this approximation and derive the conditions for its
applicability to the calculation of the phases. We account for various sources
of imperfections, ranging from higher terms in the adiabatic-elimination
expansion and irreversible population loss to couplings to additional states.
We find that, as far as the phase shifts are concerned, the adiabatic
elimination is accurate only for a very large detuning. We show that the
adiabatic approximation is a far more accurate method for evaluating the phase
shifts, with a vast domain of validity; the accuracy is further enhanced by
superadiabatic corrections, which reduce the error well below .
Moreover, owing to the effect of adiabatic population return, the adiabatic and
superadiabatic approximations allow one to calculate the phase shifts even for
a moderately large detuning, and even when the peak Rabi frequency is larger
than the detuning; in these regimes the adiabatic elimination is completely
inapplicable. We also derive several exact expressions for the phases using
exactly soluble two-state and three-state analytical models.Comment: 10 pages, 7 figure
Pulse retrieval and soliton formation in a non-standard scheme for dynamic electromagnetically induced transparency
We examine in detail an alternative method of retrieving the information
written into an atomic ensemble of three-level atoms using electromagnetically
induced transparency. We find that the behavior of the retrieved pulse is
strongly influenced by the relative collective atom-light coupling strengths of
the two relevant transitions. When the collective atom-light coupling strength
for the retrieval beam is the stronger of the two transitions, regeneration of
the stored pulse is possible. Otherwise, we show the retrieval process can lead
to creation of soliton-like pulses.Comment: 11 figure
Dark-State Polaritons for multi-component and stationary light fields
We present a general scheme to determine the loss-free adiabatic
eigensolutions (dark-state polaritons) of the interaction of multiple probe
laser beams with a coherently driven atomic ensemble under conditions of
electromagnetically induced transparency. To this end we generalize the
Morris-Shore transformation to linearized Heisenberg-Langevin equations
describing the coupled light-matter system in the weak excitation limit. For
the simple lambda-type coupling scheme the generalized Morris-Shore
transformation reproduces the dark-state polariton solutions of slow light.
Here we treat a closed-loop dual-V scheme wherein two counter-propagating
control fields generate a quasi stationary pattern of two counter-propagating
probe fields -- so-called stationary light. We show that contrary to previous
predictions,there exists a single unique dark-state polariton; it obeys a
simple propagation equation.Comment: 6 pages, 2 figure
Generalized Effective Reducibility
We introduce two notions of effective reducibility for set-theoretical
statements, based on computability with Ordinal Turing Machines (OTMs), one of
which resembles Turing reducibility while the other is modelled after Weihrauch
reducibility. We give sample applications by showing that certain (algebraic)
constructions are not effective in the OTM-sense and considerung the effective
equivalence of various versions of the axiom of choice
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