Engineering high-Q superconducting tantalum microwave coplanar waveguide resonators for compact coherent quantum...

Tantalum (Ta) has recently received considerable attention in manufacturing robust superconducting quantum circuits. Ta offers low microwave loss, high kinetic inductance compared to aluminium (Al) and niobium (Nb), and good compatibility with complementary metal-oxide-semiconductor (CMOS) technology, which is essential for quantum computing applications. Here we demonstrate the fabrication engineering of thickness-dependent high-quality-factor (high-[Formula: see text]) Ta superconducting microwave coplanar waveguide resonators. All films are deposited on high-resistivity silicon substrates at room temperature without additional substrate heating. Before Ta deposition, a niobium (Nb) seed layer is used to promote a body-centred cubic lattice ([Formula: see text]-Ta) formation. We further engineer the kinetic inductance ([Formula: see text]) of the resonators by varying Ta film thicknesses. High [Formula: see text] is a key advantage for applications because it facilitates the realisation of high-impedance, compact quantum circuits with enhanced coupling to qubits. The maximum internal quality factor [Formula: see text] of [Formula: see text]3.6 × 10⁶ in the high power regime and [Formula: see text] of [Formula: see text]4.5 × 10⁵ in the single-photon regime is achieved for 100 nm Ta which represents an improvement over previous room-temperature deposited Ta resonators on silicon substrates in the single photon regime, while the highest kinetic inductance of 0.6 pH/sq is obtained for the thinnest film, which is 40 nm. This combination of high [Formula: see text] and high [Formula: see text] highlights the potential of Ta microwave circuits for high-fidelity operation of compact quantum circuits.