Quantum coherence and control is foundational to the science and engineering of quantum systems1,2. In van der Waals materials, the collective coherent behaviour of carriers has been probed successfully by transport measurements3,4,5,6. However, temporal coherence and control, as exemplified by manipulating a single quantum degree of freedom, remains to be verified. Here we demonstrate such coherence and control of a superconducting circuit incorporating graphene-based Josephson junctions. Furthermore, we show that this device can be operated as a voltage-tunable transmon qubit7,8,9, whose spectrum reflects the electronic properties of massless Dirac fermions travelling ballistically4,5. In addition to the potential for advancing extensible quantum computing technology, our results represent a new approach to studying van der Waals materials using microwave photons in coherent quantum circuits.
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The data that support the plots within this paper and other finding of this study are available from the corresponding author upon reasonable request.
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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.