On-chip filters for high-impedance superconducting resonators in the hybrid cQED device architecture

In hybrid quantum dot (QD)-cQED systems, superconducting microwave resonators are used as mediators for non-local qubit interactions. High-impedance resonators are desirable, as the increased impedance enhances the charge-photon coupling rate and moves the system deeper into the strong spin-photon coupling regime. However, higher impedance can cause significant microwave leakage through the dc bias lines used to form the QDs. On-chip LC filters on each gate line have been shown to improve the quality factor of the high-Z resonator [1,2]. Last year, we reported direct current resistivity measurements and microwave investigations of niobium nitride (NbN) films of different thicknesses. We measured a large kinetic inductance of LK ∼ 41.2 pH/sq and sheet resistance of R_s ~ 274 Ohm/sq for 15 nm NbN thin films. I will summarize our previous findings and introduce the next step to incorporate low-pass LC filters into our current cavity design. We measured the transmission through the filters to evaluate the attenuation of different filter designs. Implementing the LC filters on the QD-cQED chip will suppress microwave leakage through the dc bias lines, resulting in a significant increase in the cavity quality factor.

[1] Mi et al., APL 110, 043502 (2017)

[2] Harvey-Collard et al., PRApplied 14, 034025 (2020)