Da Hsuan Feng

The fermion dynamical symmetry model

The bulk of contemporary research in nuclear structure physics deals with nuclei that are at least moderately collective in their low-lying states.These are usually well removed from closed shells and constitute a difficult theoretical problem. The most successful descriptions of such nuclei have neglected the many-body nature of the problem, replacing it instead with some form of single-particle field, often deformed, always violating fundamental symmetries that must be restored through projection. Such approaches allow calculations that otherwise would have been impossible, and have been central to the rapid advance in quantitative descriptions of nuclear structure.

Studies of the ground-state properties of the Lipkin-Meshkov-Glick model via the atomic coherent states

Abstract The ground-state energy of the Lipkin-Meshkov-Glick hamiltonian was estimated by the Bogoliubov-Lieb inequalities which involve the atomic coherent states. It was found that the so-called Q -representation of the pseudospin hamiltonian provides a good estimation of the ground-state energy. Furthermore, nuclear phase transitions can be vividly described by the deviations of the pseudospin from the southpole of the so-called Bloch sphere.

Quantum nonintegrability in finite systems

Abstract Quantum nonintegrability in finite systems, as viewed from geometry and dynamical symmetry breaking, is discussed in this article. The concept of quantum nonintegrability can be constructed from the mathematical structures of quantum mechanics. It is shown that there is a natural geometrical description for a quantum system, which provides a suitable stage to investigate the time-honored question of quantum-classical correspondence as well as the underlying problem of nonintegrability in quantum mechanics. The implication of dynamical symmetry breaking to quantum nonintegrability and chaos is explored.

TDHF equations of motion for algebraic hamiltonians in a coherent state representation

Abstract Time-dependent Hartee-Fock (TDHF) equations are derived for nuclear systems with internal dynamical group U(r). The coordinates which appear in the TDHF equations are the coordinates which parameterize the U(r) coherent states. The TDHF orbits for the hamiltonian H are identical with equations of motion for a classical system described by the hamiltonian function 〈 H 〉 obtained directly from the operator H . This quantum-classical correspondence facilitates interpretation of TDHF orbits. The phenomena of coexistence and critical elongation are discusses, as is the relation between the critical points of the function 〈 H 〉 and the spectral properties fo the operator H .

A thermal LBGK model for large density and temperature differences

We present a new lattice-Boltzmann method for hydrodynamic simulations, which is capable of handling very large density and temperature gradients. Unlike other LBGK models, the discrete velocities we used center at the local mean flow velocity, and their values vary according to the local temperature. The adiabatic index of the gas can be easily controlled by a parameter.

Non-Markovian Complexity in the Quantum-to-Classical Transition.

Heng-Na Xiong, Ping-Yuan Lo, Wei-Min Zhang, ∗ Franco Nori, 3 and Da Hsuan Feng Department of Physics and Center for Quantum Information Science, National Cheng Kung University, Tainan 70101, Taiwan Center for Emergent Matter Science, RIKEN, Saitama 351-0198, Japan Physics Department, The University of Michigan, Ann Arbor, Michigan, 48109-1040, USA Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan (Dated: Oct. 15, 2013)The quantum-to-classical transition is due to environment-induced decoherence, and it depicts how classical dynamics emerges from quantum systems. Previously, the quantum-to-classical transition has mainly been described with memory-less (Markovian) quantum processes. Here we study the complexity of the quantum-to-classical transition through general non-Markovian memory processes. That is, the influence of various reservoirs results in a given initial quantum state evolving into one of the following four scenarios: thermal state, thermal-like state, quantum steady state, or oscillating quantum nonstationary state. In the latter two scenarios, the system maintains partial or full quantum coherence due to the strong non-Markovian memory effect, so that in these cases, the quantum-to-classical transition never occurs. This unexpected new feature provides a new avenue for the development of future quantum technologies because the remaining quantum oscillations in steady states are decoherence-free.

Anomalous crossing frequency in odd proton nuclei.

A generic explanation for the recently observed anomalous crossing frequencies in odd proton rare earth nuclei is given. As an example, the proton 1/2[541] band in [sup 175]Ta is discussed in detail by using the angular momentum projection theory. It is shown that the quadrupole pairing interaction is decisive in delaying the crossing point and the changes in crossing frequency along the isotope chain are due to the different neutron shell fillings.

HIGH SPIN SPECTROSCOPY WITH THE PROJECTED SHELL MODEL

Abstract We review recent applications of the projected shell model to the high spin spectroscopy. In particular, various high spin phenomena related to band crossing and signature dependence, for which the standard cranked shell model encounters difficulties, are extensively discussed.

Dynamical Pauli effects and the saturation of nuclear collectivity

Abstract Global fits to B (E2; 0 1 + →2 1 + ) data using the fermion dynamical symmetry model (FSDM), the interacting boson model (IBM), and the Moller-Nix geometrical model (GM) are compared. The results indicate large dynamical Pauli effects leading to shell-dependent saturation of E2 strength consistent with the FDSM and GM, but not the IBM. The FDSM calculation is analytical with only a single adjustable parameter in each major shell, yet its accuracy rivals that of the best large-scale numerical calculations.

An algebraic fermion description of band termination and loss of collectivity in heavy nuclei

Abstract An algebraic fermion model is used to interpret the loss of E2 collectivity observed in two- and four-quasiparticle aligned bands, and the termination of collective bands at high spins in rare-earth nuclei. Both can be understood as a systematic consequence of finite angular momentum content in a coherent SU3 core.