3D-wired coaxial circuit QED I: Extension to multi-qubit devices

In order to realise superconducting circuits at a sufficient scale for useful near-term applications, an architecture is required which implements good connectivity between qubits, and allows for selective readout and control of the qubits without introducing detrimental crosstalk or decoherence. Since the number of readout and control lines increases linearly with the number of qubits, scaling up a circuit which is constrained to a 2D surface becomes increasingly difficult. Here we present the extension of our recently demonstrated 3D-wired coaxial circuit QED architecture [1] to 2D arrays of qubits. Qubits and readout LC resonators are fabricated on opposing sides of a substrate and entirely off-chip coaxial wiring is built into the chip enclosure and runs perpendicular to the chip plane. Scaling is simply achieved by the repetition of the unit cell across a 2D plane. We present the performance of multi-qubit circuits based on this architecture, including coherence times and two-qubit gate fidelities.
[1] J. Rahamim et al., Appl. Phys. Lett. 110, 222602 (2017)