Eliminating Junction Fluctuators using Epitaxial Barrier in Josephson Qubit

Before a multi-qubit solid-state quantum computer is realized, many obstacles need to be overcome. The most significant problem with any solid- state qubit implementation is strong coupling to sources of decoherence in the environment. Accordingly, identifying and removing these sources is an important prerequisite for construction of a solid-state quantum computer. Among other things, all the present-day superconducting qubits use amorphous AlO$_{x}$ as a tunnel barrier. However, there is growing evidence that the amorphous AlO$_{x}$ tunnel barriers have undesirable two-level fluctuators that adversely affect the qubit. Along this line, we have fabricated the first epitaxial Josephson phase qubit with single-crystal Al$_{2}$O$_{3}$ barrier and observed substantially reduced density of two-level fluctuators in this new type of qubit. This is the first clear evidence showing the relationship between crystallinity of the tunnel barrier and the two-level fluctuators. With this new epitaxial Josephson qubit technology, we are one-step closer to realization of a practical multi-qubit solid-state quantum computer. This talk will be focused more on the fabrication side of the epitaxial qubit and the following talk will discuss the details of its measurement.