Precision Measurement of the Microwave Dielectric Loss of Sapphire in the Quantum Regime with Parts-per-Billion Sensitivity

To better understand decoherence in superconducting qubits, the authors develop a technique to measure the loss tangent of dielectric substrates and predict the impact of dielectric loss on qubit lifetimes. This is done with no need to fabricate planar devices; the technique is independent of material platform. Measurements of sapphire in a demonstration of the approach suggest that coherence of superconducting qubits on a common form of sapphire is limited significantly by bulk dielectric loss. The same technique also shows that another form of sapphire would substantially mitigate this bulk dielectric loss and prolong qubit coherence.