Epitaxial α-Ta (110) film on a-plane sapphire substrate for superconducting qubits with long coherence times

  1. Boyi Zhou,
  2. Lina Yang,
  3. Tao Wang,
  4. Yanfu Wu,
  5. Kanglin Xiong,
  6. and Jiagui Feng
Realization of practical superconducting quantum computing requires large-scale integration of qubits with long coherence times. It has been reported that {lpha}-Ta (110) film can
greatly improve the coherence times of qubits. Compared to the commonly used {\alpha}-Ta (110) film deposited on c-plane sapphire, {\alpha}-Ta (110) film can be epitaxially grown on a-plane sapphire because of the atomic relationships at their interface. Here, we demonstrate the growth of a large-scale well-ordered quasi-single crystal {\alpha}-Ta (110) film with a low density of defects on a-plane sapphire. The root mean square of the film with thickness of 200 nm is below 0.7 nm over a 10 {\mu}m \times 10 {\mu}m area and the residual resistance ratio is as high as 15.5. Transmon qubits are also fabricated using this kind of film and show relaxation times exceeding 150 {\mu}s. These results suggest {\alpha}-Ta (110) film grown on a-plane sapphire is an alternative promising choice for large-scale superconducting circuits with long coherence times of qubits.