  Qubits on solid state devices could potentially provide the rapid control
necessary for developing scalable quantum information processors. Materials
innovation and design breakthroughs have increased functionality and coherence
of qubits substantially over the past two decades. Here we show by improving
interface between InAs as a semiconductor and Al as a superconductor, one can
reliably fabricate voltage-controlled Josephson junction field effect
transistor (JJ-FET) that can be used as tunable qubits, resonators, and coupler
switches. We find that band gap engineering is crucial in realizing a
two-dimensional electron gas near the surface. In addition, we show how the
coupling between the semiconductor layer and the superconducting contacts can
affect qubit properties. We present the anharmonicity and coupling strengths
from one and two-photon absorption in a quantum two level system fabricated
with a JJ-FET.
