Designing improved zero-pi qubits using small-area capacitors

The “hard” zero-pi qubit regime—a zero-pi qubit exponentially immune to decoherence—is inaccessible due, in part, to the large capacitance to ground of extant devices. Replacing coplanar capacitors with parallel-plate capacitors, which have dramatically smaller footprints [1, 2], reduces the ground capacitance and extends the accessible regime of present “soft” zero-pi qubits. Here, we show that the newly-accessible parameter regime enables a device with increased immunity to decoherence. We discuss potential design flaws and parameter regimes that need be avoided. Lastly, we discuss new opportunities for qubit control and further device improvements.

[1] 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).

[2] Melville, A., Woods, W., Serniak, K., et al. Low-loss parallel-plate capacitor for superconducting quantum circuits. Bulletin of the American Physical Society (2022).