Using qubits as a tool in materials science: unravelling the mystery of two-level defects in amorphous solids

Presenter: Associate Professor Jared Cole, RMIT University

Superconducting qubits are one of the best understood and most promising devices for realising controllable qubits in solid-state systems. Unfortunately they suffer from the presence of defects comprised of uncontrolled two-level systems (TLS), as do many other devices based on Josephson junctions. These defects appear randomly throughout the operating frequency range and can lead to dephasing, relaxation and imperfect control pulses. They are thought to exist within the amorphous metallic-oxides which form Josephson junctions and are also associated with the capping layer on most low temperature electronics.

Interestingly, this observation is directly related to a much older and well-known problem from solid-state physics: what is the origin of the two-level defects thought to dominate the behaviour of amorphous glasses at very low temperatures?

At present the microscopic origin of the defects in superconducting circuits remains a mystery, but recent experimental and theoretical results are bringing us closer to an answer.