Dresden 2006 – scientific programme
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TT: Tiefe Temperaturen
TT 32: Transport: Quantum Coherence and Quantum Information Systems - Part 2
TT 32.3: Talk
Thursday, March 30, 2006, 14:30–14:45, HSZ 304
Readout of a Flux Qubit Using a Capacitive Bias — •Frank Deppe1,2,3, Shiro Saito2,3, Kosuke Kakuyanagi2,3, Takayoshi Meno4, Kouichi Semba2,3, Hideaki Takayanagi2,3, and Rudolf Gross1 — 1Walther-Meissner-Institut, Garching, Germany — 2NTT Basich Research Laboratories, NTT Corporation, Atsugi, Japan — 3CREST JST, Saitama, Japan — 4NTT AT, Atsugi, Japan
A promising candidate for the basic information unit for (future) scalable solid state based quantum computing is the Mooij flux qubit [1]. It consists of a superconducting loop with 3 Josephson junctions. The flux signal of the qubit states ((anti-)clockwise circulating current) can be detected with a superconducting quantum interference device (SQUID).
We successfully implemented a novel variant of the pulse&hold switching method. Creating the SQUID bias current via a coupling capacitor instead of the usual coupling resistor allows faster switching pulses while keeping proper filtering conditions for the bias line. The bias capacitor also reduces external low frequency noise. Our setup allows a direct comparison between resistive and capacitive environment on the same qubit.
We present the results of measurements on a SQUID/flux qubit system based on nanoscale Al/AlOx/Al junctions. In time domain experiments near the qubit magic point we find a slighly reduced dephasing time T2≈150 ns for the capacitive bias compared to 250 ns for the resistive bias. The reults indicate that the impact of external low frequency on qubit phase coherence is small in our system.
Supported by: SFB 631 of the Deutsche Forschungsgemeinschaft
[1] J. E. Mooij et al., Science 285, 1036 (1999)