Fast multiplexed superconducting qubit readout with intrinsic Purcell filtering

TL;DR

This paper introduces a compact notch-filter circuit for superconducting qubit readout that uses destructive interference to eliminate Purcell decay, enabling faster and more accurate simultaneous measurement of multiple qubits.

Contribution

The authors demonstrate a novel filter design that achieves high-speed, high-fidelity multiplexed qubit readout with intrinsic Purcell filtering, improving upon previous methods.

Findings

56-ns simultaneous readout of four qubits

Average assignment fidelity of 99.77%

Highest fidelity exceeding 99.9%

Abstract

Fast and accurate qubit measurement remains a critical challenge on the path to fault-tolerant quantum computing. In superconducting quantum circuits, fast qubit measurement has been achieved using a dispersively coupled resonator with a large external linewidth. This necessitates the use of a Purcell filter that protects the qubit from relaxation through the readout channel. Here we show that a readout resonator and filter resonator, coupled to each other both capacitively and inductively, can produce a compact notch-filter circuit that effectively eliminates the Purcell decay channel through destructive interference. By utilizing linewidths as large as 42 MHz, we perform 56-ns simultaneous readout of four qubits and benchmark an average assignment fidelity of 99.77%, with the highest qubit assignment fidelity exceeding 99.9%. These results demonstrate a significant advancement in speed and fidelity for multiplexed superconducting qubit readout.