Acoustic spontaneous emission by a superconducting qubit*

Superconducting circuits are a versatile tool in developing hybrid quantum platforms, including interfacing with the bulk acoustic waves (BAWs) of pristine crystalline substrates [1]. Recent experimental work has shown that transmons have a reduced lifetime in the presence of piezoelectric thin films used to transduce microwave photons into phonons [2]. Here, we have designed a qubit architecture that extends the qubit's lifetime (T1) by an order of magnitude as compared to the previous quantum acoustic BAW device [2].
With these improvements and an increase in the electro-mechanical coupling, we observe weak dispersive interactions between the qubit and phonon. Furthermore, we measure the qubit's acoustic density of states to investigate the role of electro-mechanical coupling in limiting coherence.
[1] Y. Chu, et al. Science (2017)
[2] Y. Chu, et al. Nature (2018)