The authors thank M. Augeri, J. Birenbaum, P. Baldo, G. Fitch, M. Hellstrom, K. Magoon, A. Melville, P. Murphy, B. M. Niedzielski, B. Osadchy, D. Rosenberg, R. Slattery, C. Thoummaraj and D. Volfson at MIT Lincoln Laboratory for technical assistance. This research was funded in part by the US Army Research Office grant no. W911NF-17-S-0001, and by the Assistant Secretary of Defense for Research & Engineering via MIT Lincoln Laboratory under Air Force contract no. FA8721-05-C-0002. P.J.-H. and L.B. were partly supported by the Gordon and Betty Moore Foundation’s EPiQS Initiative through grant no. GBMF4541. L.B. acknowledges support of Agence Nationale de la Recherche through grant ANR-18-CE47-0012 (JCJC QIPHSC). This work made use of the MRSEC Shared Experimental Facilities at MIT, supported by the National Science Foundation (NSF) under award no. DMR-14-19807 and of Harvard CNS, supported by NSF ECCS under award no. 1541959. Growth of BN crystals was supported by the Elemental Strategy Initiative conducted by the MEXT, Japan and JSPS KAKENHI grant numbers JP15K21722 and JP25106006. D.R.-L. acknowledges support from Obra Social ‘la Caixa’ Fellowship. M.K. acknowledges support from the Carlsberg Foundation. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements of the US Government.