316 research outputs found
Enhancement of Intermediate-Field Two-Photon Absorption by Rationally-Shaped Femtosecond Pulses
We extend the powerful frequency-domain analysis of femtosecond two-photon
absorption to the intermediate-field regime, which involves both two- and
four-photon transitions. Consequently, we find a broad family of shaped pulses
that enhance the absorption over the transform-limited pulse. It includes any
spectral phase that is anti-symmetric around half the transition frequency. The
spectrum is asymmetric around it. The theoretical framework and results for Na
are verified experimentally. This work opens the door for rational femtosecond
coherent control in a regime of considerable absorption yields
Multi-Channel Selective Femtosecond Coherent Control Based on Symmetry Properties
We present and implement a new scheme for extended multi-channel selective
femtosecond coherent control based on symmetry properties of the excitation
channels. Here, an atomic non-resonant two-photon absorption channel is
coherently incorporated in a resonance-mediated (2+1) three-photon absorption
channel. By proper pulse shaping, utilizing the invariance of the two-photon
absorption to specific phase transformations of the pulse, the three-photon
absorption is tuned independently over order-of-magnitude yield range for any
possible two-photon absorption yield. Noticeable is a set of two-photon dark
pulses inducing widely-tunable three-photon absorption
Pulse-Bandwidth Dependence of Coherent Phase Control of Resonance-Mediated (2+1) Three-Photon Absorption
We study in detail coherent phase control of femtosecond resonance-mediated
(2+1) three-photon absorption and its dependence on the spectral bandwidth of
the excitation pulse. The regime is the weak-field regime of third perturbative
order. The corresponding interference mechanism involves a group of
three-photon excitation pathways that are on resonance with the intermediate
state and a group of three-photon excitation pathways that are near resonant
with it. The model system of the study is atomic sodium (Na), for which
experimental and numerical-theoretical results are obtained. Prominent among
the results is our finding that with simple proper pulse shaping an increase in
the excitation bandwidth leads to a corresponding increase in the enhancement
of the three-photon absorption over the absorption induced by the (unshaped)
transform-limited pulse. For example, here, a 40-nm bandwidth leads to an
order-of-magnitude enhancement over the transform-limited absorption.Comment: 23 pages, 5 figure
Population redistribution in optically trapped polar molecules
We investigate the rovibrational population redistribution of polar molecules
in the electronic ground state induced by spontaneous emission and blackbody
radiation. As a model system we use optically trapped LiCs molecules formed by
photoassociation in an ultracold two-species gas. The population dynamics of
vibrational and rotational states is modeled using an ab-initio electric dipole
moment function and experimental potential energy curves. Comparison with the
evolution of the v"=3 electronic ground state yields good qualitative
agreement. The analysis provides important input to assess applications of
ultracold LiCs molecules in quantum simulation and ultracold chemistry.Comment: 6 pages, 5 figures, EPJD Topical issue on Cold Quantum Matter -
Achievements and Prospect
MLP: a MATLAB toolbox for rapid and reliable auditory threshold estimation
In this paper, we present MLP, a MATLAB toolbox enabling auditory
thresholds estimation via the adaptive Maximum Likelihood procedure proposed
by David Green (1990, 1993). This adaptive procedure is particularly appealing for
those psychologists that need to estimate thresholds with a good degree of accuracy
and in a short time. Together with a description of the toolbox, the current text
provides an introduction to the threshold estimation theory and a theoretical
explanation of the maximum likelihood adaptive procedure. MLP comes with a
graphical interface and it is provided with several built-in, classic psychoacoustics
experiments ready to use at a mouse click
Experimental Implementation of the Deutsch-Jozsa Algorithm for Three-Qubit Functions using Pure Coherent Molecular Superpositions
The Deutsch-Jozsa algorithm is experimentally demonstrated for three-qubit
functions using pure coherent superpositions of Li rovibrational
eigenstates. The function's character, either constant or balanced, is
evaluated by first imprinting the function, using a phase-shaped femtosecond
pulse, on a coherent superposition of the molecular states, and then projecting
the superposition onto an ionic final state, using a second femtosecond pulse
at a specific time delay
Fidelity Uncertainty Characterization Leading to Robust Design
Abstract Design Optimization & MDO studies carried out at CASDE, IIT Bombay are summarized. MDO architectures using WingOpt, effective use of low fidelity design thumb rules to shrink design space for S-Duct for a combat aircraft are briefly touched upon. Robust design of systems using low fidelity analysis tools and characterization of fidelity uncertainty using sparse high fidelity evaluations is discussed in detail
Transmission of light through periodic arrays of square holes: From a metallic wire mesh to an array of tiny holes
J. Bravo-Abad, L. MartĂn-Moreno, F. J. GarcĂa-Vidal, Euan Hendry, and J. GĂłmez Rivas, Physical Review B, Vol. 76, article 241102(R) (2007). "Copyright © 2007 by the American Physical Society."A complete landscape is presented of the electromagnetic coupling between square holes forming a two-dimensional periodic array in a metallic film. By combining both experimental and theoretical results along with a first-principles Fano model, we study the crossover between the physics of metallic wire meshes (when holes occupy most of the unit cell) and the phenomenon of extraordinary optical transmission, which appears when the size of the holes is very small in comparison with the period of the array
Optimal control theory for unitary transformations
The dynamics of a quantum system driven by an external field is well
described by a unitary transformation generated by a time dependent
Hamiltonian. The inverse problem of finding the field that generates a specific
unitary transformation is the subject of study. The unitary transformation
which can represent an algorithm in a quantum computation is imposed on a
subset of quantum states embedded in a larger Hilbert space. Optimal control
theory (OCT) is used to solve the inversion problem irrespective of the initial
input state. A unified formalism, based on the Krotov method is developed
leading to a new scheme. The schemes are compared for the inversion of a
two-qubit Fourier transform using as registers the vibrational levels of the
electronic state of Na. Raman-like transitions through the
electronic state induce the transitions. Light fields are found
that are able to implement the Fourier transform within a picosecond time
scale. Such fields can be obtained by pulse-shaping techniques of a femtosecond
pulse. Out of the schemes studied the square modulus scheme converges fastest.
A study of the implementation of the qubit Fourier transform in the Na
molecule was carried out for up to 5 qubits. The classical computation effort
required to obtain the algorithm with a given fidelity is estimated to scale
exponentially with the number of levels. The observed moderate scaling of the
pulse intensity with the number of qubits in the transformation is
rationalized.Comment: 32 pages, 6 figure
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