Characterizing Niobium Nitride-Based Superconducting Coplanar Waveguide Resonators for Microwave Hybrid Circuit Quantum Electrodynamics

The high critical magnetic field and relatively high critical temperature of niobium nitride (NbN) make it a promising material for applications in superconducting quantum technology. However, NbN-based superconducting circuits are sensitive to decoherence sources such as two-level system (TLS) defects. Here, we numerically and experimentally investigate NbN superconducting microwave coplanar waveguide resonator arrays with a 100 nm thickness, capacitively coupled to a common coplanar waveguide on a silicon chip. We observe that the resonators' internal quality factor (Qᵢ) decreases fromQᵢ~ 1.07× 10⁶in a high power regime toQᵢ~ 1.36× 10⁵in the single photon regime. Data from this study is consistent with the TLS theory, which describes the TLS interactions in resonator substrates and interfaces. Moreover, we study the temperature (T) dependence ofQᵢand resonance frequencyfᵣof coplanar waveguide resonators to characterize the quasiparticle density. We observe that the increase in kinetic inductance at higher temperatures is the main reason for the frequency shift. Finally, we measurefᵣandQᵢin response to in-plane magnetic fields (B||). We verify thatQᵢstays well above10⁴up toB||= 240 mT in the photon number< \! nₚₕ \! >= 1.8 atT= 100 mK. Our results could enable the development of robust microwave superconducting circuits for circuit quantum electrodynamics at high magnetic fields required for hybrid superconducting-semiconducting quantum circuits.