Characterization of Broadband Purcell Filters with Compact Footprint for Fast Multiplexed Superconducting Qubit Readout

Abstract: Engineering the admittance of external environments connected to superconducting qubits is essential, as increasing the measurement speed introduces spontaneous emission loss to superconducting qubits, known as Purcell loss. Here, we report a broad bandwidth Purcell filter design within a small footprint, which effectively suppresses Purcell loss without losing the fast measurement speed. We characterize the filter's frequency response at 4.3 K and also estimate Purcell loss suppression by finite-element-method simulations of superconducting planar circuit layouts with the proposed filter design. The measured bandwidth is over 790 MHz within 0.29 mm$^2$ while the estimated lifetime enhancement can be over 5000 times with multiple Purcell filters. The presented filter design is expected to be easily integrated on existing superconducting quantum circuits for fast and multiplexed readout without occupying large footprint.