Interferometric Purcell suppression of spontaneous emission in a superconducting qubit

TL;DR

This paper introduces an interferometric Purcell filter for superconducting qubits that significantly suppresses spontaneous emission via destructive interference, enhancing qubit performance without additional filter components.

Contribution

The authors propose and experimentally demonstrate a novel interferometric Purcell filter that suppresses resonator-mediated decay without dedicated filter components.

Findings

Suppression exceeds 100x over 400 MHz bandwidth

Achieved suppression without impedance mismatch

Device suitable for all-pass readout applications

Abstract

In superconducting qubits, suppression of spontaneous emission is essential to achieve fast dispersive measurement and reset without sacrificing qubit lifetime. We show that resonator-mediated decay of the qubit mode to the feedline can be suppressed using destructive interference, where the readout resonator is coupled to the feedline at two points. This "interferometric Purcell filter" does not require dedicated filter components or impedance mismatch in the feedline, making it suitable for applications such as all-pass readout. We design and fabricate a device with the proposed scheme and demonstrate suppression of resonator-mediated decay that exceeds 2 orders of magnitude over a bandwidth of 400 MHz for a resonator linewidth of 13.8 MHz.