Regensburg 2007 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 3: Quantum Coherence and Quantum Information Systems I

TT 3.1: Invited Talk

Monday, March 26, 2007, 09:30–10:00, H20

Experimental investigation of superconducting flux qubits — •Evgeni Ilichev — Institute for Physical High Technology, P.O. Box

We have investigated systems consisting of one, two, three or four flux qubits. In order to determine the magnitude of the coupling energy, we have measured the magnetic susceptibility of the qubit system through their influence on the resonant properties of a weakly coupled high-quality tank circuit. We show, that the system's Hamiltonian could be completely reconstructed from measurements far away from the common degeneracy point of a flux qubit system. The subsequent measurements around this point show complete agreement with the theoretical predictions following from its Hamiltonian. The ground state anti-crossings of the system could be read-out directly from these measurements. For a three-flux-qubit system this allows the determination of the ground-state flux diagram in the complete three dimensional flux space. We have also demonstrated that the fixed coupling energy can be varied in a wide range: from several millikelvins up to several kelvins. Recently, we have also demonstrated a tuneable coupling between flux qubits.