Characterizing Neon Thin Film Growth with an NbTiN Superconducting Resonator Array

Abstract

Electrons levitating above the surface of solid neon have recently emerged as a promising platform for high-quality qubits. The morphology and uniformity of the neon growth in these systems is crucial for qubit performance in a scalable architecture. Here we report on the controlled growth and characterization of thin solid neon films using multiplexed superconducting microwave resonators. By monitoring changes in the resonant frequency and internal quality factor ($Q_i$) of an array of frequency multiplexed quarter-wave coplanar waveguide resonators, we quantify the spatial uniformity of the film. A pulsed gas deposition protocol near the neon triple point results in repeatable film formation, generating measurable shifts in frequency and variations in $Q_i$ across the resonator array. Notably, introducing a post-deposition anneal at 12 K for one hour improves the film homogeneity, as shown by the reduced resonator-to-resonator variance in frequency and $Q_i$, consistent with enhanced wetting. These results demonstrate resonator-based metrology as an in-situ tool for characterising neon film growth, directly supporting the development of electron on inert quantum solid qubit platforms.

Figures (4)

• Figure 1: (a) Render of the multiplexed hanger resonator device and (b) microwave transmission measured as a function of frequency, showing 8 distinct resonances. (c) Zoom in of resonator 4, with fit as described in Eq. \ref{['eqn:s21']}. (d) Extracted internal quality factor for resonator 4 before the second deposition with anneal, as a function of photon number, together with a fit to the data given by Eq. \ref{['eqn:qi']}. The regime studied in this paper is indicated by the black arrow.
• Figure 2: (a) $S_{21}$ measurement of resonator 4 before and after neon deposition (without anneal). (b) Relative shift in frequency and absolute change in $Q_i$ before and after neon deposition for each resonator.
• Figure 3: Relative changes in frequency and internal quality factor mapped to the resonator locations on chip for cooldowns without, (a-c), and with, (d-f), a high temperature anneal at 12 K. (a) and (d) display the mixing chamber plate temperature as a function of time during the cooldowns. (b) and (e) show the relative changes in frequency, and (c) and (f) show the relative changes in $Q_i$ post neon deposition, mapped onto the location on the chip.
• Figure 4: (a) Schematic of the analytical model of the neon-covered CPW with capacitors and inductors, (b) Estimation of Neon thickness from the analytical model and FEM simulation with Neon thickness before and after annealing