Evaluating dielectric loss in hexagonal boron nitride for high-performace quantum devices

Two-dimensional van der Waals (vdWs) materials offer a promising platform for quantum information devices owing to their crystallinity and ultra-clean interfaces. Hexagonal boron nitride (hBN) is a widely studied van der Waals dielectric material. We compared the loss tangents in hBN against other dielectric materials by fabricating parallel plate capacitors with various combinations of superconductors. We measured an ultra-low dielectric loss of 2.4e-5 with a dielectric constant of 4.4 ± 1.1 for hBN at microwave frequencies. Further, we used this parallel plate capacitor as a shunt capacitor in superconducting qubits and calculated an energy relaxation time of > 1 μs. The control experiments suggest that the measured dielectric loss is limited by fabrication process and not by the intrinsic material properties of hBN. This demonstrates that hexagonal boron nitride is an excellent material for use as a dielectric in fabricating quantum devices.