Regensburg 2004 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 29: Quantenkoh
ärenz und Quanteninformationssysteme II
TT 29.4: Vortrag
Donnerstag, 11. März 2004, 15:15–15:30, H19
Dynamic Features of a Superconducting Ring-Type Charge Qubit — •Detlef Born1, Wolfram Krech1, Vladimir Shnyrkov1, Thomas Wagner2, Evgeni Il’ichev2, Uwe Hübner2, and Hans-Georg Meyer2 — 1FSU, Institut für Festkörperphysik, 07743 Jena — 2IPHT e.V., 07702 Jena
We study dynamic properties of a special Josephson charge qubit consisting of a single-Cooper-pair transistor with capacitive gate closed by a superconducting loop.
Within the framework of a two-band model we consider analytically the features of the oppositely circulating ring currents corresponding to ground and upper quantum state, respectively, in terms of gate charge and total Josephson phase across the transistor. We determine basic device characteristics, e.g. the critical current, current-phase relationships as well as the critical loop parameter and the oppositely acting Josephson inductances belonging to the separate bands.
We observed experimentally dynamic features of the described quantum object. For this purpose, we investigated the total impedance of a configuration consisting of the ring qubit inductively coupled to the coil of a high-quality tank circuit. Measuring the phase shift between tank current and voltage (MHz range), we demonstrated the modulation of the qubit ground state impedance with respect to both electric gate voltage and magnetic flux bias. Illuminating the qubit by means of an UHF source (GHz range), we detected the effect of the (negative) inductance of the upper state.