# Mechanical Purcell Filters for Microwave Quantum Machines

## TL;DR

This paper introduces a novel mechanical Purcell filter using nanomechanical resonators in lithium niobate to improve qubit measurement in microwave quantum systems by reducing decoherence.

## Contribution

It proposes, fabricates, and characterizes a mechanical Purcell filter with a ladder topology, offering a compact and crosstalk-free alternative to electromagnetic filters.

## Key findings

- The filter exhibits a bandpass response with steep edges.
- It effectively isolates qubits from decoherence channels.
- The design is suitable for integration in microwave quantum machines.

## Abstract

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.