Gradiometric flux qubits with tunable gap

摘要: For gradiometric three-Josephson-junction flux qubits, we perform a systematic study on the tuning of minimal transition frequency, so-called qubit gap. By replacing one qubit's Josephson junctions by dc SQUID, critical current this SQUID and, in turn, gap can be tuned situ control threading loop. We present spectroscopic measurements demonstrating well-defined controllability between zero and more than 10 GHz. In future, enables to tune into out resonance with other superconducting quantum circuits, while operating at its symmetry point optimal dephasing properties. The experimental data agree very well model calculations based full Hamiltonian. From numerical fit, determine coupling charging energies junctions. derived values those measured for fabricated same chip. also demonstrate biasing qubits near trapping an odd number quanta gradiometer way, effect significant kinetic inductance, thereby obtaining valuable information design.