arXiv subjects
Publications and source records attributed to M. Grigorescu.
This work presents an older, but still interesting description of a superfluid condensate with two components (protons and neutrons), confined by time-dependent deformed harmonic oscillator potentials either in collective uniform rotation, or opposite angular oscillation.
The leading relativistic and QED corrections to the ground state energy of the three-body system (epe) are calculated numerically using a Hylleraas correlated basis set. The accuracy of the nonrelativistic variational ground state wave function is discussed with respect to the convergence properties at the increase of the basis dimension and to the variance of the energy expectation value. Recent progress in the numerical procedure used to calculate expectation values for products of various physical operators is presented. It is shown that the nonrelativistic ground state energy can be calculated with an accuracy below the level width. The corrections to this energy include the lowest order Breit interaction, the vacuum polarization potential, one and two photon exchange contributions, the annihilation interaction, and spin-spin contact terms. The relativistic effects and the residual interactions considered here decrease the one electron binding energy from the nonrelativistic value of 0.012 005 070 232 980 10(3) a.u. to 0.011 981 051 246(2) a.u..
A quasiclassical correspondent for the fermion degrees of freedom is obtained by using a time-dependent variational principle with Grassmann coherent states as trial functions. In the real parametrization provided by the canonical coordinates, these states satisfy a closure relationship, and this is used to calculate the partition function at finite temperature. The particular example considered here consists of a many-fermion system in a quantum double-well. Entanglement between the one-particle orbital states leads to deviations from the normal Fermi-Dirac distribution. This deviation is reflected in the dependence of the chemical potential on concentration. In the physical example of two adjacent CuO planes in a high-Tc superconductor, the dependence is suggestive of the pseudogap observed at temperatures T>Tc.
The collective dynamics of a many-body system is described as a special case of low-energy quantum dynamics, occurring when the ground state breaks a continuous symmetry of the Hamiltonian. This approach is applied to the spontaneous breaking of the rotational symmetry of a nuclear Hamiltonian. It is shown that the excitation operator of the isovector low-lying angular oscillations in deformed nuclei is a linear combination between angular momentum operators, which generate static rotations, and "angle" operators, which generate the transition to a rotating frame.
The effects of a voltage pulse on the localization probability for a Xe atom prepared in a pure state localized on the STM surface at 0 temperature is investigated by numerically integrating the time-dependent Schroedinger equation. In these calculations the environmental interactions are neglected, and voltage pulses of 20 and 7 ns with symmetric triangular and trapezoidal shapes are considered. The atom dynamics at an environmental temperature of 4 K is studied in the frame of a stochastic, non-linear Liouville equation for the density operator. It is shown that the irreversible transfer from surface to tip may be explained by thermal decoherence rather than by the driving force acting during the application of the voltage pulse.