Regensburg 2004 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
TT: Tiefe Temperaturen
TT 22: Quantenkoh
ärenz und Quanteninformationssysteme I
TT 22.8: Vortrag
Mittwoch, 10. März 2004, 16:15–16:30, H19
Decoherence without T2 — •Frank Wilhelm — Sektion Physik und CeNS, Ludwig-Maximilians-Universität, Theresienstr. 37, 80333 München
In order to achieve coherent manipulation of quantum states in solid-state systems, it is crucial to analyze and engineer the decoherence of the system. Traditionally, its impact is parameterized using the relaxation and dephasing times T1 and T2. In particular, T2 is the time constant of the exponential decay of quantum coherent oscillations at times longer than the bath correlation time. Recent experiments on well-controlled superconducting quantum bits show however, that T2 does not account for the complete supression of the oscillations: The overall amplitude (visibility) appears to be further reduced. In order to explain this effect, I propose a consistent model invoking an environment whose spectrum is gapped or at least supressed at low frequencies. It is shown from the exact solution of the pure dephasing case, that the coherent oscillation amplitude decays up to times of the order of the inverse infrared cutoff and then remains constant, i.e. the system quickly decoheres to a constant level although T2 defined from the long-time limit is infinite. Such baths are ubiquitous in the experiments in question, e.g. in the quasiparticle channel parallel to the Josephson junctions.