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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.