A Josephson junction is a key component designed to allow electrons to travel through quantum tunneling through a thin insulating layer connecting two superconductors. Although this structure is miniscule in size that it is invisible to the naked eye, it plays a crucial role in implementing qubits, the fundamental unit of quantum computers, by precisely controlling current and phase. This technology is now a key factor of the development of superconducting quantum computers.

Aluminum is considered the most suitable material for fabricating Josephson junctions. The naturally formed thin, uniform oxide film (Al₂O₃) provides a stable insulating layer, enabling precise control of current and phase. Furthermore, its simple and highly reproducible process facilitates large-scale quantum chip fabrication, and its low noise makes it ideal for securing long qubit (coherence time) performance. These properties have made aluminum a key material for today's superconducting quantum computers.