Berlin 2005 – scientific programme

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TT: Tiefe Temperaturen

TT 14: Symposium Superconducting Quantum Systems

TT 14.3: Fachvortrag

Saturday, March 5, 2005, 14:45–15:15, TU H104

Quantum Electrometry using the Radio-Frequency Single-Electron Transistor — •Tim Duty, Kevin Bladh, Jonas Bylander, David Gunnarsson, and Per Delsing — Chalmers University of Technology, Göteborg, Sweden

The fastest and most sensitive way to measure charge is based upon the radio-frequency single-electron transistor (RF-SET). We have employed RF-SET electrometers both as a read-out device for Josephson charge qubits, and to count individual electron and Cooper-pair charge solitons passing through an 1-D array of tunnel junctions.

Our experimental studies of Josepson charge qubits demonstrate how to mitigate the effects of non-equilibrium quasiparticles and produce Cooper-pair boxes with robust even-parity ground states. Coherent free-precession with a large visibility has been observed, and measurements of dephasing indicate the presence of low-frequency background charge fluctuations. Measured relaxation times are generally shorter than expected and not yet fully understood.

The quantum mechanical tunnelling of single charges in a one-dimensional array is time correlated and consequently the detected signal exhibits the frequency f=I/e, where I is the current and e is the electron charge. For Cooper-pairs, one observes f=I/2e. We present the first direct observation of time-correlated single-electron and Cooper-pair tunnelling oscillations.