Surface Acustic Wave filters for superconducting qubits

In an open system, the dynamical evolution of a qubit state is non-deterministic due to the stochastic noise, leading to qubit state decoherence. In the case of the qubit readout circuit, even when the readout resonator is far off-resonance, the qubit is still damped to some degree. By using a Purcell filter, qubit loss is reduced by several orders of magnitude.

In this work, we propose to use acustic wave filters, well-established in the Telecommunications industry, as a Purcell filter. Using acustic wave filters, like bulk acustic wave (BAW) or surface acoustic wave (SAW), versus the current state-of-the-art Purcell filters would provide several advantages: higher isolation of the qubit to the readout frequencies since SAW/BAW filters allow multiple transmission zeros to be placed at the qubit frequency, as well as being quite miniaturized compared to usual filter alternatives.

In this work, we characterize at qubit environmental conditions of single photon-level powers and milikelvin temperatures a 1.5 GHz LiNbO SAW resonator. We also characterize its frequency and internal quality factor dependence on temperature and drive power and infer its intrinsic loss mechanisms. This resonator design can be included into the 1.5 GHz stopband SAW filter design that we expect will improve the lifetime of our qubits.