Enhancement and inhibition of acoustic spontaneous emission from a superconducting qubit: Part I Design and characterization*

Recent experiments in quantum acoustics have demonstrated quantum coherent control of individual phonons. However, in the presence of piezoelectric materials, transmon lifetimes have been orders of magnitude lower than the state of the art. The excess loss may be attributed to parasitic loss channels introduced through electro-mechanical coupling in piezoelectric materials. Through careful microwave design and systematic testing, we have designed a qubit architecture that both suppresses acoustic spontaneous emission and increases the electro-mechanical cooperativity.

We will discuss how the qubit’s capacitive pad geometry and the crystal’s surface topography predictably change the qubit’s coherent electro-mechanical coupling and incoherent radiation into the acoustic modes of Sapphire. Our experimental approach may open the door to systematic studies of dielectric loss, a mechanism known to limit the coherence of superconducting circuits.