Characterisation of a modular 3D-integrated superconducting circuit

We present experimental results on an eight-qubit superconducting circuit comprised of fixed-frequency transmon qubits fabricated on two separate substrates and coupled together in a 1D ring topology. The device design is based on coaxial qubits with 3D-integrated readout and control [1,2] with inter-chip couplings realized capacitively between the two stacked chips. The two chips are kept separated and aligned using the sample holder in an entirely reversible assembly process requiring no additional fabrication compared to a monolithic device. We characterize the inter- and intra-chip couplings showing good agreement with electromagnetic simulation and measure crosstalk and single-qubit gate performance on par with planar monolithic devices, demonstrating the potential to build large-scale circuits based on this 3D-integrated modular approach.

[1] Rahamim et al., APL 110, 222602 (2017)

[2] Spring et al., Science Advances 8, eabl6698 (2022)