Regensburg 2010 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 36: TR: Poster Session
TT 36.31: Poster
Donnerstag, 25. März 2010, 14:00–18:00, Poster A
Gradiometric superconducting flux qubit with tunable gap — •Manuel Johannes Schwarz1, Tomasz Niemczyk1,2, Frank Deppe1, Achim Marx1, and Rudolf Gross1,2 — 1Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, Walther-Meissner-Str. 8, 85748 Garching — 2Physics Department, TU München, 85748 Garching
One promising candidate for the implementation of scalable quantum information processing is a superconducting flux qubit. In its gradiometric version, it consists of two galvanically coupled superconducting loops with three or four nanoscale Josephson junctions, one of them being slightly smaller than the others, placed on the shared line. In principle, the qubit transition frequency can be controlled by applying an external flux to the loop. However, in order to maintain long phase coherence time, the qubit must be operated at a certain optimal flux bias. Nevertheless, tunability can be obtained by replacing the smaller junction with a DC SQUID loop acting as an effective junction, whose critical current can be varied via an additional flux line without changing the flux bias in the qubit loop [1]. Using electron beam lithography, two-angle shadow evaporation and Al technology, we have fabricated such a device together with a readout SQUID. At 30 mK, we observe a clear qubit signature in the switching current of the readout SQUID. Furthermore, we show the results of spectroscopic measurements and discuss to which extent an additional flux through the small SQUID loop affects this data. This work is supported by the DFG via SFB631 and NIM.
[1] F.G. Paauw et al., Phys. Rev. Lett. 102, 090501 (2009)