Mitigation of dielectric loss in aluminium-based superconducting transmon qubits*

Recent months have seen a jump in qubit coherence as a result of new materials exploration, surpassing the values that seemed to have reached a plateau in the traditional aluminium-based devices.

A pressing limitation of superconducting qubits is dielectric loss at surface interfaces caused by parasitic two-level systems. These two-level systems can reside at substrate-air, metal-air, or substrate-metal interfaces. However, these interfaces do not contribute equally to the overall dielectric loss. In this work we devise experiments to pinpoint the source of these losses, and show strategies to mitigate them.

We discuss various surface treatments and show the effect they have on qubit coherence, improving it beyond values usually observed in aluminium-based devices.