Phase dependence of localization in the driven two-level modelC. E. Creffield
Dipartimento di Fisica, Università di Roma "La Sapienza" Piazzale Aldo Moro 2, I-00185, Roma, Italy
(Received 10 March 2004; accepted in final form 6 April 2004)
A two-level system subjected to a high-frequency driving field can exhibit an effect termed "coherent destruction of tunneling", in which the tunneling of the system is suppressed at certain values of the frequency and strength of the field. This suppression becomes less effective as the frequency of the driving field is reduced, and we show here how the detailed form of its fall-off depends on the phase of the driving, which for certain values can produce small local maxima (or revivals) in the overall decay. By considering a square-wave driving field, which has the advantage of being analytically tractable, we show how this surprising behavior can be interpreted geometrically in terms of orbits on the Bloch sphere. These results are of general applicability to more commonly used fields, such as sinusoidal driving, which display a similar phenomenology.
03.65.Xp - Tunneling, traversal time, quantum Zeno dynamics.
33.80.Be - Level crossing and optical pumping.
03.67.Lx - Quantum computation.
© EDP Sciences 2004