Regensburg 2004 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 29: Quantenkoh
ärenz und Quanteninformationssysteme II

TT 29.10: Vortrag

Donnerstag, 11. März 2004, 17:00–17:15, H19

Cavity QED using superconducting qubits - intermediate temperatures — •Göran Johansson, Alexander Shnirman, and Ileana Rau — Institut für Theoretische Festkörperphysik

Inspired by recent experiments we investigate the dynamics of a Josephson qubit resonantly coupled to a damped harmonic oscillator. We specifaclly investigate the temperature dependence of the cavity susceptebility, which in solid state devices corresponds to the impedance of the LC-circuit. At zero temperature the uncoupled resonant peak is Rabi splitted by the qubit. At temperatures comparable to the oscillator frequency we find an intricate multiple peak structure, while at high temperatures the uncoupled single peak is recovered. We treat the dynamics of the system numerically by exact diagonalizing of the qubit plus up to 100 states in the oscillator. We then include the bath within the Bloch-Redfield formalism, without making the secular approximation. Specifically we investigate the break-down of the secular approximation at finite temperatures, caused by the Liouvillian degeneray, i.e. two or more transitions with approximately equal energy. In the impedance this is seen as the overlap of nearby peaks, which cannot be calculated as the sum of the two peaks.