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Hexagonal boron nitride as a low-loss dielectric for superconducting quantum circuits and qubits

Abstract

Dielectrics with low loss at microwave frequencies are imperative for high-coherence solid-state quantum computing platforms. Here 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 aluminium Josephson junctions to realize transmon qubits with coherence times reaching 25 μs, 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 with conventional all-aluminium 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.

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Fig. 1: Superconducting resonators for characterizing the microwave dielectric loss of hBN.
Fig. 2: Internal quality factor Qi of hBN-coupled LC resonators.
Fig. 3: Transmon qubits shunted by PPCs.
Fig. 4: Characterization of fixed-frequency and flux-tunable transmon qubits shunted by PPCs.

Data availability

The data that supports the findings of this study are available from the corresponding author upon reasonable request and with the cognizance of our US Government sponsors who funded the work.

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Acknowledgements

We acknowledge helpful discussions with G. Calusine, T. Hazard, D. Klein, D. MacNeill, K. O’Brien, A. Di Paolo and A. Vepsäläinen. We thank R. Das at MIT Lincoln Laboratory for technical assistance. This research was funded in part by the US Army Research Office grant number W911NF-18-S-0116, by the National Science Foundation QII-TAQS grant number OMA-1936263, and by the Assistant Secretary of Defense for Research & Engineering via MIT Lincoln Laboratory under Air Force contract number FA8721-05-C-0002. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan (grant number JPMXP0112101001) and JSPS KAKENHI (grant numbers 19H05790 and JP20H00354). 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.

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Contributions

J.I-J.W. and M.A.Y. conceived and designed the experiment. M.A.Y. performed the microwave simulation. J.I-J.W., M.A.Y., Q.L., T.D., D.K., A.J.M., B.M.N, K.S., J.L.Y. and M.E.S. contributed to the device fabrication. J.I-J.W., M.A.Y., A.H.K., S.E.M., B.K., Y.S., J.B., S.G. and R.W. participated in the measurements. M.A.Y., J.I-J.W. and A.H.K analysed the data. K.W. and T.T. grew the hBN crystal. J.I-J.W. and W.D.O. led the paper writing, and all other authors contributed to the text. T.P.O., S.G., P.J-H. and W.D.O supervised the project.

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Correspondence to Joel I-J. Wang, Pablo Jarillo-Herrero or William D. Oliver.

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Nature Materials thanks Mark Hersam and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Figs. 1–4 and Table 1.

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Wang, J.IJ., Yamoah, M.A., Li, Q. et al. Hexagonal boron nitride as a low-loss dielectric for superconducting quantum circuits and qubits. Nat. Mater. 21, 398–403 (2022). https://doi.org/10.1038/s41563-021-01187-w

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