Quantum chaos in the mesoscopic device for the Josephson flux qubit

E. POZZO, D. DOMINGUEZ AND M. J. SÁNCHEZ

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

Año: 2008 vol. 77 p. 24518 - 24527

0163-1829

We study the quantum spectra and eigenfunctions of the three-junction superconducting quantum interference device designed for the Josephson flux qubit at high energies. We analyze the spectral statistics of the parameter region where the system has a mixed classical phase space where regular and chaotic orbits can be found at the same classical energy. We perform a numerical calculation of eigenvalues and eigenstates for different values of the ratio of the Josephson and charging energies, EJ/EC, which is directly related to an effective parameter. We find that the nearest-neighbor distributions P(s) of the energy-level spacings are well fitted by the Berry-Robnik theory employing as free parameters the pure classical measures of the chaotic and regular regions of phase space in the different energy regions in the semiclassical case. The phase-space representation of the wave functions is obtained via the Husimi distributions, and the localization of the states of classical structures is analyzed. We discuss for which values of EJ/EC it can be possible to perform experiments that could be sensitive to the structure of a mixed classical phase space.