Modern nanotechnology allows one to scale down various important devices (sensors, chips, fibers, etc.) and thus opens up new horizons for their applications. The efficiency of most of them is based on fundamental physical phenomena, such as transport of wave excitations and resonances. Short propagation distances make phase-coherent processes of waves important. Often the scattering of waves involves propagation along different paths and, as a consequence, results in interference phenomena, where constructive interference corresponds to resonant enhancement and destructive interference to resonant suppression of the transmission. Recently, a variety of experimental and theoretical work has revealed such patterns in different physical settings. The purpose of this review is to relate resonant scattering to Fano resonances, known from atomic physics. One of the main features of the Fano resonance is its asymmetric line profile. The asymmetry originates from a close coexistence of resonant transmission and resonant reflection and can be reduced to the interaction of a discrete (localized) state with a continuum of propagation modes. The basic concepts of Fano resonances are introduced, their geometrical and/or dynamical origin are explained, and theoretical and experimental studies of light propagation in photonic devices, charge transport through quantum dots, plasmon scattering in Josephson-junction networks, and matter-wave scattering in ultracold atom systems, among others are reviewed.

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Fano resonances in nanoscale structures

The authors review the development of extended x-ray absorption fine structure (EXAFS) within the last decade. Advances in experimental techniques have been largely stimulated by the availability of synchrotron radiation. The theory of EXAFS has also matured to the point where quantitative comparison with experiments can be made. The authors review in some detail the analysis of EXAFS data, starting from the treatment of raw data to the extraction of distances and amplitude information, and they also discuss selected examples of applications of EXAFS chosen to illustrate both the strength and limitations of EXAFS as a structural tool.

Extended x-ray absorption fine structure—its strengths and limitations as a structural tool

We summarize the problem of measuring an ultrashort laser pulse and describe in detail a technique that completely characterizes a pulse in time: frequency-resolved optical gating. Emphasis is placed on the choice of experimental beam geometry and the implementation of the iterative phase-retrieval algorithm that together yield an accurate measurement of the pulse time-dependent intensity and phase over a wide range of circumstances. We compare several commonly used beam geometries, displaying sample traces for each and showing where each is appropriate, and we give a detailed description of the pulse-retrieval algorithm for each of these cases.

Measuring ultrashort laser pulses in the time-frequency domain using frequency-resolved optical gating

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. Among numerous theoretical insights and technological improvements that produced the present state-of- the-art in quantum control, there have been several breakthroughs of foremost importance. On the technology side, the current experimental successes would be impossible without the development of intense femtosecond laser sources and pulse shapers. On the theory side, the two most critical insights were (i) realizing that ultrafast atomic and molecular dynamics can be controlled via manipulation of quantum interferences and (ii) 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 (AFC), 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 AFC experiments is guided by a learning algorithm, with stochastic methods proving to be especially effective. AFC 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

https://iopscience.iop.org/article/10.1088/1367-2630/12/7/075008/pdf

Control of quantum phenomena: past, present and future

We present $GW$ calculations for small and large gap systems comprising typical semiconductors (Si, SiC, GaAs, GaN, ZnO, ZnS, CdS, and AlP), small gap semiconductors (PbS, PbSe, and PbTe), insulators (C, BN, MgO, and LiF), and noble gas solids (Ar and Ne). It is shown that the ${G}_{0}{W}_{0}$ approximation always yields too small band gaps. To improve agreement with experiment, the eigenvalues in the Green's function $G$ $(G{W}_{0})$ and in the Green's function and the dielectric matrix $(GW)$ are updated until self-consistency is reached. The first approximation leads to excellent agreement with experiment, whereas an update of the eigenvalues in $G$ and $W$ gives too large band gaps for virtually all materials. From a pragmatic point of view, the $G{W}_{0}$ approximation thus seems to be an accurate and still reasonably fast method for predicting quasiparticle energies in simple $sp$-bonded systems. We furthermore observe that the band gaps in materials with shallow $d$ states (GaAs, GaN, and ZnO) are systematically underestimated. We propose that an inaccurate description of the static dielectric properties of these materials is responsible for the underestimation of the band gaps in $G{W}_{0}$, which is itself a result of the incomplete cancellation of the Hartree self-energy within the $d$ shell by local or gradient corrected density functionals.

Self-consistent G W calculations for semiconductors and insulators

Electronic Excitations in Condensed Rare Gases

Using theory to guide the choice of pulse shape, we have synthesized frequency-chirped laser pulses and used them to control the evolution of vibrational wave packets on the $B$ excited state of iodine. A negatively chirped pulse produces a wave packet at the target time localized about an internuclear position and momentum of our choice. An approximately time-reversed pulse, however, produces a delocalized wave packet. The experimental results are in very good qualitative agreement with quantum simulations.

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Quantum Control of Wave Packet Evolution with Tailored Femtosecond Pulses.

III. Sample Preparation and Morphology 1492 IV. Photon-Induced Dissociation 1493 V. Perfect Caging 1494 A. Direct Observation of the Caging Process 1494 B. Stabilization of Fragments and Isomerization 1495 1. OClO 1495 2. ICN 1496 VI. Predissociation 1497 A. Electronic Caging by Solvent Symmetry 1497 B. Differential Solvation 1497 VII. Dissociation through Sudden Cage Exit 1499 A. F(2P) 1500 B. O(1D) 1500 C. S(1D) 1500 VIII. Delayed versus Sudden Exit 1500 A. HI, HCl 1500 B. H2O, D2O 1502 C. H2S, D2S 1502 D. Cl2 in XesDissociation without Cage Exit 1502 IX. Forced and Delayed Cage Exit 1503 A. Cl2 in Ar 1503 B. Cl2 in Kr and Xe 1504 X. Channeled Migration 1504 A. F Atoms 1504 B. O Atoms 1505 C. H Atoms 1506 XI. Photon-Induced Harpooning 1508 XII. Acknowledgments 1510 XIII. References 1510

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Molecular Photodynamics in Rare Gas Solids.

Photoelectron energy distributions for solid Ne, Ar, Kr, and Xe have been measured for $8 \mathrm{eV}l~\ensuremath{\hbar}\ensuremath{\omega}l~30 \mathrm{eV}$ by use of synchrotron radiation. From these we obtained the total width and structure of the valence bands. Our data demonstrate that almost all available band-structure calculations fail to predict quantitatively features other than the spin-orbit splitting. Photoelectron energy distributions for Xe in Ar and Xe in Ne support this viewpoint.

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Photoemission from Rare-Gas Solids: Electron Energy Distributions from the Valence Bands

Extended-x-ray-absorption fine-structure spectra in the region of the $\mathrm{Cu} K$ edge are presented for Cu, CuO, ${\mathrm{Cu}}_{2}$O, CuS${\mathrm{O}}_{4}$, CuS${\mathrm{O}}_{4}$\ifmmode\cdot\else\textperiodcentered\fi{}5${\mathrm{H}}_{2}$O, Cu${(\mathrm{OH})}_{2}$, Cu(N${\mathrm{O}}_{3}$)\ifmmode\cdot\else\textperiodcentered\fi{}3${\mathrm{H}}_{2}$O, ${[\mathrm{C}\mathrm{u}{(\mathrm{N}{\mathrm{H}}_{3})}_{4}]}^{2+}$, and Cu${\mathrm{Br}}_{2}$. By the usual Fourier-analysis method, bond lengths for Cu-O, Cu-N, and Cu-Br are determined. Further, a back-transformation into real space is used which allows us to check the consistency of the evaluation for the whole energy range investigated. The advantages of this evaluation are: bond lengths can be taken from regions of high accuracy of the experimental data, the $k$ dependence of the phase shifts can be checked and this presentation gives a criterion on how to fit the reference energy necessary for the energy-momentum conversion. The bond lengths determined with this method agree to within 0.02 \AA{}A with reliable x-ray diffraction data.

Nikolaus Schwentner

Papers

Electronic Excitations in Condensed Rare Gases

Quantum Control of Wave Packet Evolution with Tailored Femtosecond Pulses.

Molecular Photodynamics in Rare Gas Solids.

Photoemission from Rare-Gas Solids: Electron Energy Distributions from the Valence Bands

Improved extended-x-ray-absorption fine-structure (EXAFS) studies applied to the investigation of Cu-O, Cu-N, and Cu-Br bond lengths