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1
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Dynamics of the Electric Field in a GaAs/AlGaAs Superlattice after Femtosecond Optical Excitation: Application of Time-Resolved Spectroscopic Techniques

100%
Lisauskas A., Blöser C., Sachs R., Roskos H., Juozapavičius A., Valušis G., Köhler K.
Acta Physica Polonica A
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2005
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vol. 107
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issue 2
250-255
EN
We apply time-resolved photocurrent and differential electroreflectance spectroscopy to study the evolution of the internal field in a GaAs/AlGaAs superlattice after pulsed optical excitation at low temperature. The electric field dynamics is investigated by tracing the spectral position of the Wannier-Stark transitions as a function of delay time. We determine the electron sweep-out time, extract detailed information about the picosecond-time-scale drift of the charge carriers by comparing the measured data with the results of semi-classical self-consistent model calculations, and evaluate the two experimental techniques with respect to their ability to provide information about the carrier and field dynamics.
2
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Quantum Invariants Descending from the Joule-Lenz Law for the Dissipated Energy Applied in Calculating the Rate of Electron Transitions

100%
Olszewski S.
Acta Physica Polonica A
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2017
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vol. 131
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issue 2
226-231
EN
The Joule-Lenz law for a classical expense of energy is transformed into a formula representing a quantum-mechanical invariant composed of the interval of energy connected with an electron transition and the corresponding interval of transition time between two quantum levels. Time and energy enter the invariant formula on an equal footing, moreover the time intervals converge with the time periods characteristic for the examined quantum systems. These properties imply to consider the time intervals as quanta of time having character similar to that possessed by the energy. Another result of the transformation of the Joule-Lenz law is the time rate of energy of the quantum transitions. This rate is calculated on a fully non-probabilistic way. When examined for the hydrogen atomic spectrum taken as an example, the obtained quantum rate is by many orders larger than a classical transition rate.
3
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Semiclassical Motion of Systems with Internal States

100%
Stenholm S.
Acta Physica Polonica A
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1994
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vol. 86
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issue 1
51-60
EN
In many fields of atomic and molecular physics we need to combine the center-of-mass motion with internal degrees of freedom. In this work, the classical motion in phase space is separated from the quantum processes by a multiple-time-scale approach. The expansion parameter is proportional to Planck's constant. The theory is given and illustrated by examples: the semiclassical description of a particle without internal states, the extraction of a classical trajectory and the derivation of the light-induced force.
4
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Electronic Structure of Organometallic Complexes of f Elements. Are Molecular Orbital Calculations a Useful Tool for Spectroscopists?

100%
Jank S., Amberger H.
Acta Physica Polonica A
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1996
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vol. 90
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issue 1
21-32
EN
The crystal field parameters of base-free (Me_{3}SiC_{5}H_{4})_{3}Pr, (C_{5}H_{5})_{3}Pr·NCCH_{3}, (C_{5}H_{5})_{3}La(NCCH_{3})_{2}:Pr, [Pr(C_{8}H_{8})]^{+} and Nd[N(SiMe_{3})_{2}]_{3} as model compound for Nd[CH(SiMe_{3})_{2}]_{3} were inserted into the corresponding energy matrices of a model spin-free f^{1} system. Diagonalizing these matrices the crystal field splitting patterns of the f orbitals were calculated. These experimentally based molecular orbital schemes are compared with the results of previous model calculations.
5
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Quantum Graphology

100%
Kottos T.
Acta Physica Polonica A
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2006
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vol. 109
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issue 1
7-21
EN
We review quantum chaos on graphs. We construct a unitary operator which represents the quantum evolution on the graph and study its spectral and wave function statistics. This operator is the analogue of the classical evolution operator on the graph. It allows us to establish a connection between the corresponding periodic orbits and the statistical properties of eigenvalues and eigenfunctions. Specifically, for the energy-averaged spectral form factor we derived an exact combinatorial expression which illustrate the role of correlations between families of isometric orbits. We also show that enhanced wave function localization due to the presence of short unstable periodic orbits and strong scarring can rely on completely different mechanisms
6
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Classical Paths and Semiclassical Ghosts

100%
Haake F.
Acta Physica Polonica A
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1994
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vol. 85
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issue 4
693-698
EN
The semiclassical approximation for the quantum propagator of the kicked top is shown to involve not only classical periodic orbits but also complex generalizations thereof. Such ghost trajectories have complex actions S and thus contribute exponentially small terms as ħ → O. However, close to bifurcations ImS can be very small whereupon ghosts become quite visible.
7
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Analysis of Missing Level Statistics for Microwave Networks Simulating Quantum Chaotic Graphs Without Time Reversal Symmetry - the Case of Randomly Lost Resonances

80%
Ławniczak M., Białous M., Yunko V., Bauch S., Dietz B., Sirko L.
Acta Physica Polonica A
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2017
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vol. 132
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issue 6
1672-1676
EN
We present experimental and numerical studies for level statistics in incomplete spectra obtained with microwave networks simulating quantum chaotic graphs with broken time reversal symmetry. We demonstrate that, if resonance frequencies are randomly removed from the spectra, the experimental results for the nearest-neighbor spacing distribution, the spectral rigidity and the average power spectrum are in good agreement with theoretical predictions for incomplete sequences of levels of systems with broken time reversal symmetry.
8
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Aspects of Integrability in a Classical Model for Non-Interacting Fermionic Fields

80%
Grosse-Holz S., Engl T., Richter K., Urbina J.
Acta Physica Polonica A
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2015
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vol. 128
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issue 6
994-1001
EN
In this work we investigate the issue of integrability in a classical model for non-interacting fermionic fields. This model is constructed via classical-quantum correspondence obtained from the semiclassical treatment of the quantum system. Our main finding is that the classical system, contrary to the quantum system, is not integrable in general. Regarding this contrast it is clear that in general classical models for fermionic quantum systems have to be handled with care. Further numerical investigation of the system showed that there may be islands of stability in the phase space. We also investigated a similar model that is used in theoretical chemistry and found this one to be most probably integrable, although also here the integrability is not assured by the quantum-classical correspondence principle.
9
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Fading Statistics in Communications - a Random Matrix Approach

80%
Yeh J., Ott E., Antonsen T., Anlage S.
Acta Physica Polonica A
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2011
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vol. 120
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issue 6A
A-85-A-88
EN
Fading is the time-dependent variations in signal strength measured at a receiver, due to temporally evolving multipath scattering and interference. In our previous work we introduced a statistical fading model for the time-reversal invariant case by combining the predictions of random matrix theory with the random coupling model that includes system-specific properties such as the radiation impedance of the ports and short-orbit effects. In the high-loss limit this random matrix theory model reduced to the most common fading models in the wireless communication field. In this paper we discuss the theoretical model in more detail and extend it to the case of broken time-reversal invariance.
10
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Doorway Mechanism in Many-Body Systems and in Quantum Billiards

80%
Guhr T.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
741-748
EN
Among the numerous different ways to excite many-body and other complex quantum systems, mechanisms are often found which are clearly distinguished by a simple, typically semiclassical interpretation. In nuclei, these are the collective excitations in which all or large groups of particles move coherently. They often act as "doorways" to other excitations of single-particle character. Examples for and the limitations of the doorway mechanism are discussed. Recent results show that superscars in the barrier billiard serve as perfect object to shed light on aspects of the doorway mechanism which are not directly accessible in traditional quantum systems. To this end, two new statistical observables are employed. Some open questions are addressed.
11
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The Wavefunctions and Energy Eigenvalues of the Schrodinger Equation for Different Potentials Due to the Virial Theorem

80%
Arslan H., Hulaguhanoglu N.
Acta Physica Polonica A
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2015
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vol. 127
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issue 4
914-916
EN
The derivation of the virial theorem is presented both in classical and quantum mechanical approach. The kinetic energy and potential energy of the mechanical energy is converted to each other due to the virial theorem. Some of the different potentials are considered. For some of these potentials, the wavefunctions and energy eigenvalues of the Schrödinger Equation are derived.
12
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Motion Center in Quantum Wave Packet Dynamics

80%
Liu Q., Yu Y., Pan H., Wang Z.
Acta Physica Polonica A
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2015
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vol. 127
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issue 3
761-766
EN
We seek for an oscillating center solution of the wave function satisfying the Schrödinger equation for a nonrelativistic charge particle in an arbitrary external field, where the oscillating center of physical system is a motion governing by a guidance formula of the classical mechanics and at the same time, the physical system obeys the rule of quantum mechanics. In terms of our approach, one enables to know how quantum process may actually come about. The results are applied to analyze the Landau level. We explain successfully that the orbit of oscillator center for the Landau level is circle.
13
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Experimental Control of the Number of Ionized Donors in an AlGaAs/GaAs Heterostructure

80%
Denk P., Schlösser T., Ensslin K., Holland M.
Acta Physica Polonica A
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1995
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vol. 88
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issue 5
977-981
EN
The high mobility of electrons in AlGaAs-GaAs heterostructures relies on the concept of modulation doping. As a sample is cooled down to T = 4.2 K under a fixed gate bias the number of ionized donors can be frozen and is then independent on the gate potential. We discuss the consequences of this procedure on the electron density and mobility in a two-dimensional electron gas. For a laterally patterned sample we find that the amplitude of the potential modulation can be maximized for a given carrier density by a suitably chosen cool-down voltage.
14
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Semiclassical Double-Inequality on Heisenberg Uncertainty Relation in 1D

80%
Bering K.
Acta Physica Polonica A
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2016
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vol. 129
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issue 6
1093-1099
EN
We prove a double-inequality for the product of uncertainties for position and momentum of bound states for 1D quantum mechanical systems in the semiclassical limit.
15
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Scattering from a Ring Graph - A~Simple Model for the Study of Resonances

80%
Waltner D., Smilansky U.
Acta Physica Polonica A
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2013
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vol. 124
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issue 6
1087-1090
EN
Scattering from the very simple ring graph is shown to display several basic features which underlie the complex (chaotic) phenomena observed in scattering from more complex graphs. In particular we demonstrate the appearance of arbitrarily narrow resonances - the "topological resonances" which are directly linked to the existence of cycles. We use the ring graph to study the response of such resonances to perturbations induced by a time-dependent random noise.
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