Microwave dielectric loss of hexagonal Boron Nitride in the low-temperature, single-photon regime*

The use of 2D van der Waals (vdW) heterostructures in quantum computing devices, due in part to the potential of combining different materials with epitaxial precision, has begun to merge the superconducting and 2D material platforms. Hexagonal boron nitride (hBN), a vdW material widely used as an ultra-clean substrate, gate dielectric, and protection layer in vdW heterostructures, may be used in building high-quality Josephson elements and qubit capacitors. VdW materials have been extensively studied in the DC and optical regimes, but understanding their response to microwave excitations is vital to introducing them into superconducting circuits. We study hBN in the microwave regime by integrating the material in a superconducting LC resonator to extract its loss tangent. Our scheme can be used for characterizing not only the electromagnetic properties of hBN, but also other 2D materials.