Dresden 2006 – scientific programme

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TT: Tiefe Temperaturen

TT 1: Superconductivity: Tunnelling, Josephson Junctions, SQUIDs

TT 1.3: Talk

Monday, March 27, 2006, 10:00–10:15, HSZ 02

Characterisation of Nb charge-phase qubit circuits at 4.2 — •J. Könemann, H. Zangerle, B. Mackrodt, R. Dolata, S.A. Bogoslovsky, M. Götz, and A.B. Zorin — Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany

Due to their scalability superconducting circuits, based on small Josephson junctions, are promising candidates for qubits, which form the basis of a possible quantum computing processor. The Bloch transistor included in a superconducting loop can serve as a so-called charge-phase qubit. Our all-Nb circuits with junction area down to 80 nm by 80 nm and nominal critical current of individual junctions of 25-50 nA included the Bloch transistor inserted into a loop and on-chip inductor of the tank circuit. Due to appreciable charging energy of the island the critical current of the transistor was substantially suppressed. High temperature made this suppression stronger. We report the radio-frequency measurements of our Nb qubit circuits, which were possible at 4.2 K. Resonance and flux modulation curves were used to determine the characteristic parameters of the samples. From the phase modulation curves the critical current (as small as few nA) and almost harmonic phase dependence of supercurrent were found. These data are consistent with our estimation based on a multi-band quantum-statistical model.