Frequency-Domain Coherent Control of Femtosecond Two-Photon Absorption: Intermediate-Field vs. Weak-Field Regime

Coherent control of femtosecond two-photon absorption in the intermediate-field regime is analyzed in detail in the powerful frequency domain using an extended 4th-order perturbative description. The corresponding absorption is coherently induced by the weak-field non-resonant two-photon transitions as well as by four-photon transitions involving three absorbed photons and one emitted photons. The interferences between these two groups of transitions lead to a difference between the intermediate-field and weak-field absorption dynamics. The corresponding interference nature (constructive or destructive) strongly depends on the detuning direction of the pulse spectrum from half the two-photon transition frequency. The model system of the study is atomic sodium, for which both experimental and theoretical results are obtained. The detailed understanding obtained here serves as a basis for coherent control with rationally-shaped femtosecond pulses in a regime of sizable absorption yields.Comment: 25 pages, 5 figure

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

Dimension-specific attention directs learning and listening on auditory training tasks

The relative contributions of bottom-up versus top-down sensory inputs to auditory learning are not well established. In our experiment, listeners were instructed to perform either a frequency discrimination (FD) task ("FD-train group") or an intensity discrimination (ID) task ("ID-train group") during training on a set of physically identical tones that were impossible to discriminate consistently above chance, allowing us to vary top-down attention whilst keeping bottom-up inputs fixed. A third, control group did not receive any training. Only the FD-train group improved on a FD probe following training, whereas all groups improved on ID following training. However, only the ID-train group also showed changes in performance accuracy as a function of interval with training on the ID task. These findings suggest that top-down, dimension-specific attention can direct auditory learning, even when this learning is not reflected in conventional performance measures of threshold change

Boundary conditions for interfaces of electromagnetic (photonic) crystals and generalized Ewald-Oseen extinction principle

The problem of plane-wave diffraction on semi-infinite orthorhombic electromagnetic (photonic) crystals of general kind is considered. Boundary conditions are obtained in the form of infinite system of equations relating amplitudes of incident wave, eigenmodes excited in the crystal and scattered spatial harmonics. Generalized Ewald-Oseen extinction principle is formulated on the base of deduced boundary conditions. The knowledge of properties of infinite crystal's eigenmodes provides option to solve the diffraction problem for the corresponding semi-infinite crystal numerically. In the case when the crystal is formed by small inclusions which can be treated as point dipolar scatterers with fixed direction the problem admits complete rigorous analytical solution. The amplitudes of excited modes and scattered spatial harmonics are expressed in terms of the wave vectors of the infinite crystal by closed-form analytical formulae. The result is applied for study of reflection properties of metamaterial formed by cubic lattice of split-ring resonators.Comment: 15 pages, 8 figures, submitted to PR

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$_{2}$ 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