A trilayer process for the fabrication of Al phase qubits

Herein we develop an Al/AlO _x /Al trilayer process, feasible to fabricate complex circuits with wiring crossovers, for the preparation of Al junctions and phase qubits. The AlO _x layer is obtained by in situ thermal oxidation, which provides high-quality junction tunnel barriers. The Al junctions show a considerably low leakage current and the Josephson critical current density can be conveniently controlled in the range of a few to above 100 A/cm², which is favorable in the phase qubit application. Macroscopic quantum tunneling, energy spectrum, energy relaxation time, Rabi oscillation, and Ramsey interference of the Al phase qubits are measured, demonstrating clearly quantum coherent dynamics with a timescale of 10 ns. Further improvements of the coherent dynamic properties of the device are discussed.