Damping of the states in a two-level system with crossing terms

Andrea Sacchetti

While the phenomenon of the exact crossing of energy levels is a rarely occurring event, in the case of quantum resonances associated with metastable states this phenomenon is much more frequent and various scenarios can occur. When there is an exact crossing of the imaginary parts of the resonances in a two-level quantum system subject to an external DC electric field, then a damped beating phenomenon occurs, which is absent if there is no such crossing. This fact, tested numerically on an explicit one-dimensional model, suggests the possibility of designing quantum sensors to determine in a very simple way whether the external field strength has an assigned value or not.

W. Zwerger

Ya. D. Klubis

R. Rouse, Siyuan Han, James E. Lukens

We report the first observation of resonant tunneling of a system between two macroscopically distinct states: energy levels in different fluxoid wells of a weakly damped superconducting quantum interference device which differ in mean current by approximately 6 \ensuremath{\mu}A. Near 50 mK, the tunneling rate $\ensuremath{\gamma}({\ensuremath{\Phi}}_{x})$ from the metastable well vs applied flux ${\ensuremath{\Phi}}_{x}$ is found to exhibit a series of local maxima where the levels (spaced by $\ensuremath{\approx}1.9$ K) in the two wells cross. The positions of these maxima agree well with the level crossings calculated using independently determined system parameters.

A. Widom, Yogendra Narain Srivastava, Terrence D. Clark

In a standard two-level model of macroscopic quantum tunneling between two potential wells, the damping is described by coupling into a thermal oscillator bath. When the oscillator bath is classical and the two-level system is quantum mechanical, the free energy of the total system is that of the two systems with no interactions. The result is discussed in terms of the Bohr view of quantum measurements.

Vladimir I Kogan, Valerii S. Lisitsa, A.D. Selidovskin