Marlies Goorden¹ und •Frank Wilhelm^2
1Dpt. of Applied Physics, Delft University of Technology, The Netherlands
²Sektion Physik and CeNS, Ludwig-Maximilians-Universität, München

Superconducting persistent current quantum bits, small superconducting loops interrupted by three Josephson junction, are a promising candidate for performing manipulations of the quantum state of a macroscopic device, in particular for the realization of a quantum computer [1]. Recently, it has been shown, that such devices can be brought in superpositions of clockwise and counterclockwise current states, which can be viewed as Schrödinger's cat states.

The influence of the decohering environment to this device can be analyzed in terms of the spin-boson model. We present a detailed theoretical and numerical analysis of the driven spin-boson model based on the Bloch-Redfield formalism. We do in detail discuss the properties of linear and nonlinear resonances of this system and perform a comparison to recent experiments, which allows to infer the coherence and driving properties of the system. We moreover analyze the possibility to optimize single-qubit gates in a hostile environment using pulse-shaping techniques.

[1] C.H. van der Wal et al., Science 290, 773 (2000).