In circuit quantum electrodynamics, measuring the state of a superconducting qubit introduces a loss channel which can enhance spontaneous emission through the Purcell effect, thus decreasing qubit lifetime. This decay can be mitigated by performing the measurement through a Purcell filter which forbids signal propagation at the qubit transition frequency. If the filter is also well-matched at the readout cavity frequency, it will protect the qubit from decoherence channels without sacrificing measurement speed. We propose and analyze design for a mechanical Purcell filter, which we also fabricate and characterize at room temperature. The filter is comprised of an array of nanomechanical resonators in thin-film lithium niobate, connected in a ladder topology, with series and parallel resonances arranged to produce a bandpass response. The modest footprint, steep band edges, and absence of cross-talk in these filters make them a novel and appealing alternative to analogous electromagnetic versions currently used in microwave quantum machines.
@article{arxiv.1905.08403,
title = {Mechanical Purcell Filters for Microwave Quantum Machines},
author = {Agnetta Y. Cleland and Marek Pechal and Pieter-Jan C. Stas and Christopher J. Sarabalis and Amir H. Safavi-Naeini},
journal= {arXiv preprint arXiv:1905.08403},
year = {2020}
}