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P. Rozmej

Publications and source records attributed to P. Rozmej.

At least 19 recordsLinked to original sources
arXiv2004

Spin-orbit entanglement in time evolution of radial wave packets in hydrogenic systems

Time evolution of radial wave packets built from the eigenstates of Dirac equation for a hydrogenic systems is considered. Radial wave packets are constructed from the states of different $n$ quantum number and the same lowest angular momentum. In general they exhibit a kind of breathing motion with dispersion and (partial) revivals. Calculations show that for some particular preparations of the wave packet one can observe interesting effects in spin motion, coming from inherent entanglement of spin and orbital degrees of freedom. These effects manifest themselves through some oscillations in the mean values of spin operators and through changes of spatial probability density carried by upper and lower components of the wave function. It is also shown that the characteristic time scale of predicted effects (called $T_{\mathrm{ls}}$) is for radial wave packets much smaller than in other cases, reaching values comparable to (or even less than) the time scale for the wave packet revival.

quant-ph↗
arXiv2003

Semiclassical catastrophes and accumulative angular squeezing of a kicked quantum rotor

We present a detailed theory of spectacular semiclassical catastrophes happening during the time evolution of a kicked quantum rotor (Phys.Rev. Lett. {\bf 87}, 163601 (2001)). Both two- and three-dimensional rotational systems are analyzed. It is shown that the wave function of the rotor develops a {\em cusp} at a certain delay after a kick, which results in a sharply focused rotational wave packet. The {\em cusp} is followed by a fold-type catastrophe manifested in the {\em rainbow}-like moving angular singularities. In the three-dimensional case, the rainbows are accompanied by additional singular features similar to {\em glory} structures known in wave optics. These catastrophes in the time-dependent angular wave function are well described by the appropriate tools of the quasiclassical wave mechanics, i.e. by Airy and Bessel approximations and Pearcey's functions. A scenario of "accumulative squeezing" is also presented in which a specially designed train of short kicks produces an unlimited narrowing of the rotor angular distribution. This scenario is relevant for the molecular alignment by short laser pulses, and also for atom lithography schemes in which cold atoms are focused by an optical standing wave.

quant-ph↗
arXiv2002

Relativistic precession and spin dynamics of an elliptic Rydberg wave packet

Time evolution of wave packets built from the eigenstates of the Dirac equation for a hydrogenic system is considered. We investigate the space and spin motion of wave packets which, in the non-relativistic limit, are stationary states with a probability density distributed uniformly along the classical, elliptical orbit (elliptic WP). We show that the precession of such a WP, due to relativistic corrections to the energy eigenvalues, is strongly correlated with the spin motion. We show also that the motion is universal for all hydrogenic systems with an arbitrary value of the atomic number Z.

quant-ph↗
arXiv2002

Stability and instability of a hot and dilute nuclear droplet. II. Dissipative isoscalar modes

Results on dissipative isoscalar modes of a hot and dilute nuclear droplet are presented. As compared to the adiabatic limit (part I), realistic dissipation yields a substantial reduction of the growth rates for all unstable modes, while the area of spinodal instability in the ($\varrho$,T)-plane remains unchanged. The qualitative features of multifragmentation through spinodal decomposition as obtained in the adiabatic limit are not significantly affected by dissipation.

nucl-th↗
arXiv2001

Spin-orbit pendulum in Dirac oscillator

The dynamics of wavepackets in a relativistic Dirac oscillator (DO) is considered. A comparison to nonrelativistic spin-orbit pendulum effect is discussed. Particular relativistic effects, like Zitterbewegung in spin motion, are found in Dirac representation. This trembling motion disappears in Foldy-Wouthuysen representation. A substantial difference between the dynamics of wavepackets corresponding to circular and linear orbits of a particle is obtained and discussed.

quant-ph↗
arXiv2000

Stability and instability of a hot and dilute nuclear droplet

The diabatic approach to collective nuclear motion is reformulated in the local-density approximation in order to treat the normal modes of a spherical nuclear droplet analytically. In a first application the adiabatic isoscalar modes are studied and results for the eigenvalues of compressional (bulk) and pure surface modes are presented as function of density and temperature inside the droplet, as well as for different mass numbers and for soft and stiff equations of state. We find that the region of bulk instabilities (spinodal regime) is substantially smaller for nuclear droplets than for infinite nuclear matter. For small densities below 30% of normal nuclear matter density and for temperatures below 5 MeV all relevant bulk modes become unstable with the same growth rates. The surface modes have a larger spinodal region, reaching out to densities and temperatures way beyond the spinodal line for bulk instabilities. Essential experimental features of multifragmentation, like fragmentation temperatures and fragment-mass distributions (in particular the power-law behavior) are consistent with the instability properties of an expanding nuclear droplet, and hence with a dynamical fragmentation process within the spinodal regime of bulk and surface modes (spinodal decomposition).

nucl-ex↗
arXiv2000

Spin dynamics of wave packets evolving with the Dirac Hamiltonian in atoms with high Z

The motion of circular WP for one electron in central Coulomb field with high Z is calculated. The WP is defined in terms of solutions of the Dirac equation in order to take into account all possible relevant effects in particular the spin-orbit potential. A time scale is defined within which spin dynamics must be taken into account mainly in the atoms with high Z. Within this time scale there exists a mechanism of collapses and revivals of the spin already shown by the authors for harmonic oscillator potential and called the 'spin-orbit pendulum'. However this effect has not the exact periodicity of the simpler model, but the WP's spatial motion is nevertheless quite similar.

quant-ph↗
arXiv1999

Squeezed angular momentum coherent states: construction and time evolution

A family of angular momentum coherent states on the sphere is constructed using previous work by Aragone et al [1]. These states depend on a complex parameter which allows an arbitrary squeezing of the angular momentum uncertainties. The time evolution of these states is analyzed assuming a rigid body hamiltonian. The rich scenario of fractional revivals is exhibited with cloning and many interference effects.

quant-ph↗
arXiv1999

Spin-orbit pendulum - Relativistic extension

We discuss an extension of the theory of {\em spin-orbit pendulum} phenomenon given in [1] to relativistic approach. It is done within the so called Dirac Oscillator. Our first results, focusing on circular wave packet motion have been published recently [2]. The scope of this paper is motion of a linear wave packet. In relativistic approach we found {\em Zitterbewegung} in spin-orbit motion (in Dirac representation) due to coupling to negative energy states. This effect is washed out in the Foldy-Wouthuysen representation. Another important change with respect to non-relativistic case is the loss of periodicity. The phenomenon reminds the time evolution of population inversion in Jaynes-Cummings model.

quant-ph↗
arXiv1999

Pictures of quantum nuclear rotation beyond the correspondence principle

We analyze the time evolution of simple nuclear rotational wave packets (WP) called circular, linear or elliptic, depending on squeezing parameter $η$, assuming that $E=\hbarω_0 I(I+1)$. The scenario of fractional revivals found by Averbukh and Perelman is adapted to symmetric WP and compared to that which holds for asymmetric WP. In both cases various shapes are identified under these lines in particular many cases of cloning. 'Mutants' WP are found most often. Finally the time evolution of a WP formed by Coulomb excitation on $^{238}$U and calculated by semiclassical theory is also presented.

quant-ph↗
arXiv1999

The Dirac Oscillator. A relativistic version of the Jaynes--Cummings model

The dynamics of wave packets in a relativistic Dirac oscillator is compared to that of the Jaynes-Cummings model. The strong spin-orbit coupling of the Dirac oscillator produces the entanglement of the spin with the orbital motion similar to what is observed in the model of quantum optics. The collapses and revivals of the spin which result extend to a relativistic theory our previous findings on nonrelativistic oscillator where they were known under the name of `spin-orbit pendulum'. There are important relativistic effects (lack of periodicity, zitterbewegung, negative energy states). Many of them disappear after a Foldy-Wouthuysen transformation.

quant-ph↗
arXiv1998

A Phase in a Coherent State Wave Function - Is It Always Irrelevant?

We point out that harmonic oscillator coherent states, in coordinate representation, require particular phase factor, in order to represent classical time evolution properly. The presence of such a phase is clearly stated only in a minority of scientific sources discussing properties of coherent states.

quant-ph↗
arXiv1998

Towards new understanding of nuclear rotation

Properties of time evolution of wave packets built up from rotator eigenstates are discussed. The mechanism of perfect cloning of the initial wave packet for "circular states" at fractional revival times is explained. The smooth transition from "circular" to "linear" through intermediate "elliptic" is described. Example of time evolution of a nuclear wave packet created in Coulomb excitation mechanism is presented.

quant-ph↗
arXiv1998

Clones and other interferance effects in the evolution of angular momentum coherent states

The aim of this article is to present the interference effects which occur during the time evolution of simple angular wave packets (WP) which can be associated to a diatomic rigid molecule (heteronuclear) or to a quantum rigid body with axial symmetry like a molecule or a nucleus. The time evolution is understood entirely within the frame of fractional revivals discovered by Averbukh and Perelman since the energy spectrum is exactly quadratic. Our objectives are to study how these interference effects differ when there is a change of the initial WP. For this purpose we introduce a two parameter set of angular momentum coherent states. From one hand this set emerge quite naturally from the three dimensional coherent states of the harmonic oscillator, from another hand this set is shown to be buit from intelligent spin states.We have also compared our coherent states to some previously constructed using boson representation of angular momentum. The time evolution of coherent states for symmetric top is also discussed.

quant-ph↗
arXiv1997

New mechanism of collapse and revival in wave packet dynamics due to spin-orbit interaction

The article discusses the properties of time evolution of wave packets in a few systems. Dynamics of wave packet motion for Rydberg atoms with the hierarchy of collapses and revivals is briefly reviewed. The main part of the paper focuses on the new mechanism of quantum reccurrences in wave packet dynamics. This mechanism can occur (in principle) in any physical system with strong enough spin-orbit interaction. We discuss here the SPIN_ORBIT PENDULUM effect that consists in different motions of subpackets possessing different spin fields and results in oscillations of a fraction of average angular momentum between spin and ordinary subspaces. The evolution of localized wave packet into toroidal objects and backwards (for other class of initial conditions) is also subject to discussion.

quant-ph↗
arXiv1997

Time dependent partial waves and vortex rings in the dynamics of wave packets

We have found a new class of time dependent partial waves which are solutions of time dependent Schrödinger equation for three dimensional harmonic oscillator. We also showed the decomposition of coherent states of harmonic oscillator into these partial waves. This decomposition appears perticularly convenient for a description of the dynamics of a wave packet representing a particle with spin when the spin--orbit interaction is present in the hamiltonian. An example of an evolution of a localized wave packet into a torus and backwards, for a particular initial conditions is analysed in analytical terms and shown with a computer graphics.

quant-ph↗