Ramsey fringes at different operating frequencies Dephasing time obtained by spin-echo


Coherent Operation of a Gap-Tunable Flux Qubit

By replacing the smallest Josephson junction of the qubit with a DC-SQUID, we demonstrate the in situ coherent tunability of the gap of a superconducting flux qubit. In a conventional design, the tunneling energy of the flux-qubit is fixed in the fabrication process. However, in the new device, we can control qubit tunneling energy in nano second while keeping the qubit at its degeneracy point (optimum flux bias) where the flux-noise is considered to be minimum. From Ramsey fringes and echo-measurement, the best dephasing time of T2=0.6 μs in this type of flux-qubit are obtained. This improved device will accelerate research of quantum information processing via quantum bus and quantum memory. (Page 31)

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