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Level Crossing (level + crossing)

Distribution by Scientific Domains
Physics and Astronomy60%
Chemistry40%

Selected Abstracts

Muon Implantation of Metallocenes: Ferrocene

CHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2007
Upali
Abstract Muon Spin Relaxation and Avoided Level Crossing (ALC) measurements of ferrocene are reported. The main features observed are five high field resonances in the ALC spectrum at about 3.26, 2.44, 2.04, 1.19 and 1.17,T, for the low-temperature phase at 18,K. The high-temperature phase at 295,K shows that only the last feature shifted down to about 0.49,T and a muon spin relaxation peak at about 0.106,T which approaches zero field when reaching the phase transition temperature of 164,K. A model involving three muoniated radicals, two with muonium addition to the cyclopentadienyl ring and the other to the metal atom, is postulated to rationalise these observations. A theoretical treatment involving spin-orbit coupling is found to be required to understand the Fe,Mu adduct, where an interesting interplay between the ferrocene ring dynamics and the spin-orbit coupling of the unpaired electron is shown to be important. The limiting temperature above which the full effect of spin-orbit interaction is observable in the ,SR spectra of ferrocene was estimated to be 584,K. Correlation time for the ring rotation dynamics of the Fe,Mu radical at this temperature is 3.2,ps. Estimated electron g values and the changes in zero-field splittings for this temperature range are also reported. [source]

A single qubit Landau-Zener gate

FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 1 2003
V.G. Benza
We study the hamiltonian and dissipative dynamics of a system undergoing a sequence of level crossings. The resulting Landau-Zener effect makes a new implementation of a general single qubit gate possible. In the dissipative case, with a periodic bias, the level crossing counteracts the interlevel relaxation and drives the system toward a two dimensional attractor. This feature can in principle be used to implement quantum memory devices of new type. [source]

Exponentially accurate quasimodes for the time-independent Born,Oppenheimer approximation on a one-dimensional molecular system

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2005
George A. Hagedorn
Abstract We consider the eigenvalue problem for a one-dimensional molecular-type quantum Hamiltonian that has the form where h(y) is an analytic family of self-adjoint operators that has a discrete, nondegenerate electronic level ,(y) for y in some open subset of ,. Near a local minimum of the electronic level ,(y) that is not at a level crossing, we construct quasimodes that are exponentially accurate in the square of the Born,Oppenheimer parameter , by optimal truncation of the Rayleigh,Schrödinger series. That is, we construct an energy E, and a wave function ,,, such that the L2 -norm of ,, is ,,(1) and the L2 -norm of (H(,) , E,),, is bounded by , exp(,,/,2) with , > 0. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source]

A single qubit Landau-Zener gate

FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 1 2003
V.G. Benza
We study the hamiltonian and dissipative dynamics of a system undergoing a sequence of level crossings. The resulting Landau-Zener effect makes a new implementation of a general single qubit gate possible. In the dissipative case, with a periodic bias, the level crossing counteracts the interlevel relaxation and drives the system toward a two dimensional attractor. This feature can in principle be used to implement quantum memory devices of new type. [source]

The Hubbard model extended by nearest-neighbor Coulomb and exchange interaction on a cubic cluster , rigorous and exact results

ANNALEN DER PHYSIK, Issue 6 2010
R. Schumann
The Hubbard model on a cube was revisited and extended by both nearest-neighbor Coulomb correlation W and nearest-neighbor Heisenberg exchange J. The complete eigensystem was computed exactly for all electron occupancies and all model parameters ranging from minus infinity to plus infinity. For two electrons on the cluster the eigensystem is given in analytical form. For six electrons and infinite on-site correlation U we determinded the groundstate and the groundstate energy of the pure Hubbard model analytically. For fixed electron numbers we found a multitude of ground state level crossings depending on the various model parameters. Furthermore the groundstates of the pure Hubbard model in dependence on a magnetic field h coupled to the spins are shown for the complete U-h plane. The critical magnetic field, where the zero spin groundstate breaks down is given for four and six electrons. Suprisingly we found parameter regions, where the ground state spin does not depend monotonously on J in the extended model. For the cubic cluster gas, i.e. an ensemble of clusters coupled to an electron bath, we calculated the density n (,, T, h) and the thermodynamical density of states from the grand potential. The ground states and the various spin-spin correlation functions are studied for both attractive and repulsive values of the three interaction constants. We determined the various anomalous degeneration lines, where n (,, T = 0, h = 0) shows steps higher than one, since in this parameter regions exotic phenomena as phase separation are to expect in extended models. For the cases where these lines end in triple points, i.e. groundstates of three different occupation numbers are degenerated, we give the related parameter values. Regarding the influence of the nn-exchange and the nn-Coulomb correlation onto the anomalous degeneration we find both lifting and inducing of degeneracies depending on the parameter values. [source]