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P Cejnar

Publications and source records attributed to P Cejnar.

7 recordsLinked to original sources
PubMed2004

Experimental confirmation of the Alhassid-Whelan arc of regularity.

Evidence is presented to show that a group of nuclei, spanning a range of structures, corresponds to a previously proposed isolated region of regular behavior between vibrational and rotational structures that was never before observed empirically. Nuclei predicted to show such regular spectra correspond to Hamiltonian parameters that lie amidst those giving more chaotic spectra. We identify a key observable that has a one-to-one correspondence to this arc of regularity and which therefore provides both an empirical signature for it and a clue to its underlying nature.

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PubMed2002

Triple point of nuclear deformations.

We show that the second-order phase transition between spherical and deformed shapes of atomic nuclei is an isolated point following from the Landau theory of phase transitions. This point can occur only at the junction of two or more first-order phase transitions which explains why it is associated with one special type of structure and requires the recently proposed first-order phase transition between prolate and oblate nuclear shapes. Finally, we suggest the first empirical example of a nucleus located at the isolated triple-point.

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PubMed2001

Decoherence and thermalization in a simple bosonic system.

Properties of a parameter-dependent quantum system with the Hamiltonian H(lambda) randomized by fluctuations of the parameter lambda in a narrow range are investigated. The model employed (the interacting boson model-1) exhibits a crossover behavior at a critical parameter value. Due to the fluctuations, individual eigenstates /psi(alpha)(lambda)> of the Hamiltonian become statistical ensembles of states [density matrices rho(alpha)(lambda)], which allows us to study effects related to the decoherence and thermalization. In the decoherence part, we evaluate von Neumann and information entropies of the density matrices rho(alpha)(lambda) and the overlaps of the eigenstates of the density matrix with various physically relevant bases. An increased decoherence at the " phase transitional" point and an exceptional role of the dynamic-symmetry U(5) basis are discovered. In the part devoted to the thermalization, we develop a method of how a given density matrix rho(alpha)(lambda) can be represented by an equivalent canonical (thermal) ensemble. Thermodynamic consequences of the quantum "phase transition" (related, in particular, to the specific heat of the thermal equivalent) are discussed.

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PubMed2000

Quantum phase transitions studied within the interacting boson model

We study quasicritical phenomena in transitions between two "quantum phases" of a finite boson system, described by the interacting boson model 1 used in nuclear physics. The model is formulated in the algebraic framework and has a simple geometrical interpretation; the "phases" represented by dynamical symmetries U(5) and SU(3) correspond to spherical and deformed nuclear shapes. The quasicriticality of the U(5)-SU(3) transition is shown to be connected with the following phenomena simultaneously occurring in a narrow parameter region between the symmetries: (a) abrupt structural changes of eigenstates, (b) multiple avoided crossing of levels, (c) peaked density of exceptional points, (d) qualitative changes of the corresponding classical potential. We show that these spectroscopic features influence the dynamics of intersymmetry transitions in the model parameter space if the parameters themselves become dynamical variables.

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