High-Q superconducting microwave resonators using MBE titanium nitride

Anand Ithepalli; Haoran Lu; Eegene Clara Chung; Xiangqin Wang; Amit Rohan Rajapurohita; Keun-Yeol Park; Celesta S. Chang; Peter McMahon; Huili Grace Xing; David Muller; Valla Fatemi; Debdeep Jena

arXiv · 2607.15230

High-Q superconducting microwave resonators using MBE titanium nitride

Anand Ithepalli·Haoran Lu·Eegene Clara Chung·Xiangqin Wang·Amit Rohan Rajapurohita·Keun-Yeol Park·Celesta S. Chang·Peter McMahon·Huili Grace Xing·David Muller·Valla Fatemi·Debdeep Jena

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Abstract

Using molecular beam epitaxy, we have realized thin films of titanium nitride (TiN) on c-plane sapphire that exhibit the lowest observed full-width at half maximum X-ray rocking curve width of 18 arcsec. Though the (111) oriented TiN exhibits an abrupt and crystalline interface with sapphire, for the first time we observe sub-surface defects in the sapphire substrate, which nucleate structural defects in the epitaxial TiN layer. Using quarter-wavelength coplanar waveguide (CPW) resonators in a 3 \textmu m/6 \textmu m/3 \textmu m gap/strip/gap lines in a hanger geometry, we find the internal quality factor of the TiN resonators to be $>10^{6}$ in the single-photon $\langle n \rangle \sim 1$ limit at 5.8 GHz and 10 mK, rising to $>20 \times 10^{6}$ at $\langle n \rangle \sim 10^{6}$. The results are of high interest for applications of superconducting TiN in several areas, and provide a path towards epitaxial Josephson junctions with crystalline barriers in the future for high coherence qubits.

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Anand Ithepalli, Haoran Lu, Eegene Clara Chung, Xiangqin Wang, Amit Rohan Rajapurohita, Keun-Yeol Park, Celesta S. Chang, Peter McMahon, Huili Grace Xing, David Muller, Valla Fatemi, Debdeep Jena. 2026-07-16. High-Q superconducting microwave resonators using MBE titanium nitride. https://arxiv.org/abs/2607.15230

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