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Dielectrics with low loss at microwave frequencies are imperative for high-coherence solid-state quantum computing platforms. We study the dielectric loss of hexagonal boron nitride (hBN) thin films in the microwave regime by measuring the quality factor of parallel-plate capacitors (PPCs) made of NbSe2-hBN-NbSe2 heterostructures integrated into superconducting circuits. The extracted microwave loss tangent of hBN is bounded to be at most in the mid-10-6 range in the low temperature, single-photon regime. We integrate hBN PPCs with aluminum Josephson junctions to realize transmon qubits with coherence times reaching 25 $mu$s, consistent with the hBN loss tangent inferred from resonator measurements. The hBN PPC reduces the qubit feature size by approximately two-orders of magnitude compared to conventional all-aluminum coplanar transmons. Our results establish hBN as a promising dielectric for building high-coherence quantum circuits with substantially reduced footprint and, with a high energy participation that helps to reduce unwanted qubit cross-talk.
Low-dimensional wide bandgap semiconductors open a new playing field in quantum optics using sub-bandgap excitation. In this field, hexagonal boron nitride (h-BN) has been reported to host single quantum emitters (QEs), linking QE density to perimete
The loss of amorphous hydrogenated silicon nitride (a-SiN$_{x}$:H) is measured at 30 mK and 5 GHz using a superconducting LC resonator down to energies where a single-photon is stored, and analyzed with an independent two-level system (TLS) defect mo
When a crystal is subjected to a periodic potential, under certain circumstances (such as when the period of the potential is close to the crystal periodicity; the potential is strong enough, etc.) it might adjust itself to follow the periodicity of
We investigate the effect of surface acoustic waves on the atomic-like optical emission from defect centers in hexagonal boron nitride layers deposited on the surface of a LiNbO$_3$ substrate. The dynamic strain field of the surface acoustic waves mo
Optically addressable spins in materials are important platforms for quantum technologies, such as repeaters and sensors. Identification of such systems in two-dimensional (2d) layered materials offers advantages over their bulk counterparts, as thei