The effective potentials of the rf-SQUID and three-Josephson junction loop with a penetrating external magnetic flux are studied. Using the periodic boundary condition for the phase evolution of the wave function of Cooper pairs, we obtain new periodic potentials with cusp barriers in contrast with the usual smooth double-well potential. The tunneling through the cusp barrier becomes dominant for a parameter regime where the self inductance of the superconducting loop and the Josephson coupling energy are large. Calculating the tunneling frequency we see that the cusp potential may offer a more efficient qubit.

No abstract

No abstract

We model a four-site tight-binding Aharonov-Bohm (AB) ring whose sites house dispersionless Einstein phonons. The resonant tunnelling of an electron through the AB ring in the presence of a time-periodic magnetic flux which threads the ring is investigated. The Floquet scattering approach is followed within the electron-phonon Fock space. The Ricatti matrix method, a nonperturbative pruning technique, is utilized to extract the transmission properties of the system from the time-dependent Schrödinger equation. We observe additional satellite peaks in the total transmission graphs representing the photon-assisted tunnelling, as well as side resonances due to the phononassisted tunnelling. There happen to exist unusually stiff main transmission peaks that are not disturbed by the strong time-periodic magnetic flux, a finding attributed to the geometric characteristics of the AB ring.

No abstract