3D Integration with Protected Qubits*

Large-scale quantum computation will require 3D integrated architectures to achieve all-to-all connectivity, individual qubit addressability, and protection against crosstalk and decoherence channels. A central challenge in 3D quantum hardware is ensuring that additional materials and structures (such as dielectrics) do not suppress qubit lifetimes. Thus far, 3D integration schemes have typically involved a vacuum region between the qubit and other structures to avoid dielectric loss [1,2,3]. In this talk, we propose to use intrinsically protected qubits for 3D integration: resistance to dielectric loss allows for simple layered structures similar to classical 3D architectures. We show that disjoint support in fluxonium qubits leads to relaxation times ~10ms, even when low-quality-factor SiN is deposited on top. We demonstrate a two-layer fluxonium device fabricated with techniques common in single-layer processing. The ideas explored here will allow for simple, repeatable fabrication processes for 3D quantum processors based on protected qubits.

[1] Rosenberg et. al. npj Quantum Information 3, 42 (2017).
[2] Brecht et. al. npj Quantum Information 2, 16002 (2016).
[3] Foxen et. al. Quantum Sci. Technol. 3, 014005 (2018).