A New Technique to Measure Microwave Dielectric Material Loss*

Qubit coherence time is essential in quantum computation, since, in tandem with gate speed, it governs the number of coherent operations one can eventually perform on a quantum computer. In the field of circuit quantum electrodynamics, a qubit is often formed by the non-linearity of a Josephson junction fabricated on a dielectric substrate. Therefore, any dielectric loss in the substrate can be an important contribution to qubit coherence. Indeed, recent studies suggest that among different qubit loss channels dielectric loss may be a substantial one. In this talk, we describe a sensitive method to selectively measure microwave dielectric substrate loss and present preliminary measurements with the technique.