26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

High-impedance TiN resonators for flip-chip integration with SiMOS electron spin qubits

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Poster ANZOS | Quantum Computing and Quantum Information (ANZCOP QCQI)

Description

Coupling electron spins to microwave photons directly is a challenge, due to the intrinsically weak magnetic dipole interaction. To overcome this, most work involved creating an artificial spin-orbit coupling (SOC) via micromagnets. This, however, imposes spatial constraints on device scaling. Recently, it was shown that the intrinsic SOC in SiMOS spin qubits can be heavily amplified by operating at orbitals degeneracies, without micromagnets [1]. The coupling strength scales with the resonator’s zero-point voltage fluctuation, motivating high-kinetic-inductance superconducting films. Furthermore, the high temperature processing of silicon MOS qubits is known to severely degrade resonator quality factors [2, 3]. Utilizing a flip-chip architecture allows the separation of the fabrication of the resonator and qubit chips [3]. We report half-wavelength TiN coplanar waveguide resonators with a sheet kinetic inductance of L_(k,□) ≈ 150 pH/□ at a thickness of 15nm. Counter-intuitively, maximizing resonator impedance is not always optimal in a flip-chip geometry. A low-impedance top-chip fanout creates an impedance discontinuity at the inter-chip transition, leading to partial reflections and a finite-impedance optimum in the gate-voltage zero-point fluctuations. Following this, we design for a characteristic impedance of ~590 Ω for a width of 5μm. Hanger-mode resonators show resonance frequencies in quantitative agreement with predictions across seven resonators, with internal quality factors up to Q_i ~ 116,000. ABCD matrix analysis and CST simulations of the flip-chip geometry predict a zero-point voltage fluctuation of V_zpf ≈ 3.6 µV at the quantum dot gate near 6 GHz, corresponding to a spin–photon coupling of g_eff/2π ≈ 0.7 MHz when using transverse spin-orbit coupling parameters extracted from pulsed electron spin-orbital spectroscopy (PESOS) measurements on comparable Si-MOS devices [1].

References
[1] Guo, W., Feng, M. et al., arXiv:2308.12626 (2023).
[2] Yu, C. X. et al., Nature Nanotechnology 18, 741 (2023).
[3] Granel, S. et al., arXiv:2604.25871 (2026).