Flux Qubits with Long Coherence Times for Hybrid Quantum Circuits
  We present measurements of superconducting flux qubits embedded in a three dimensional copper cavity. The qubits are fabricated on a sapphire substrate and are measured by coupling them inductively to an on-chip superconducting resonator located in the middle of the cavity. At their flux-insensitive point, all measured qubits reach an intrinsic energy relaxation time in the 6-20 microseconds range and a pure dephasing time comprised between 3 and 10 microseconds. This significant improvement over previous works opens the way to the coherent coupling of a flux-qubit to individual spins. 
Michael Stern, Gianluigi Catelani, Yuimaru Kubo, Cecile Grezes, Audrey   Bienfait, Denis Vion, Daniel Esteve, Patrice Bertet
cond-mat.mes-hall cond-mat.supr-con