Quantum systems with external parameters

Marek Pechal

S. I. Ali

Abstract This paper examines the dynamics of a W-configuration four-level atom in a quantized cavity field and the system driven by an external classical field. By applying some canonical transformations, we derive analytical solutions to the Schrödinger equation for the corresponding Hamiltonian. We have analyzed the impact of the external field and detuning parameters on the system’s relative entropy of coherence, Wigner function, and Pancharatnam phase. Our findings suggest that the external field parameter greatly affects the coherence of the system, whereas the detuning parameters may increase its maximum bounds. Furthermore, we have utilized the Wigner function as a tool to measure the quantumness and classicality of the system in its phase space. Our results indicate that the external field has a greater impact on the classicality of the system than the detuning parameters. Additionally, we have observed rapid oscillations in the dynamics of the Pancharatnam phase for large detuning values. It is worth noting that the external field reduces the number of phase jumps in the system.

L. E. Reichl

J. Oitmaa, Z Weihong

As an extension of a one-parameter series expansion, a two-parameter expansion technique for quantum spin systems is developed. As examples of the method the authors present results for three different models on the square lattice: the (2+1)-dimensional Ising model with an external magnetic field, and the Heisenberg antiferromagnet with both an external staggered parallel magnetic field and an external perpendicular magnetic field. Analysis of the resulting series is also presented.

V. M. Kolomietz, S. V. Radionov

Within random matrix model, the response of a complex quantum system Ĥ(q[t]) on time variations in an external parameter q. In the limit of weak coupling of the external parameter to the quantum system, the different dynamical regimes of the diffusion in a space of the occupancies of eigenstates of Ĥ(q) are considered. The main focus is made on measuring the role of memory effects in the quantum diffusive dynamics. Possible macroscopic manifestations of the quantum mechanical diffusion are discussed in the context of the cranking approach, where the time variations in the classical parameter q provides the constancy of energy of the total system.

Heinz K. H. Siedentop