Strong coupling of a transmon qubit to propagating surface acoustic waves

Recently, a transmon qubit predominantly coupling to propagating Surface Acoustic Waves (SAW) was experimentally demonstrated [1]. The coupling was achieved by forming the shunting capacitance of the qubit into an interdigital transducer (IDT). By choosing a material with strong piezoelectricity, it is possible to reach coupling strengths where the spontaneous emission rate is comparable to the qubit level splitting. In this study, we theoretically explore the effect of increasing the coupling beyond the previously analysed weak coupling regime [2]. In particular, we analyse the case when the smallest energy scale of the problem is the transmon anharmonicity. In the limit of vanishing anharmonicity, we recover the classical linear description from our full quantum model.

[1] M. Gustafsson, et. al. Science, 1245993 (2014)
[2] A. F. Kockum, et al. Phys. Rev. A 90, 013837 (2014)