3D-integrated tunable transmon qubits with long coherence time and low crosstalk

Large-scale quantum computers with more than a thousand qubits are expected to be built within the next decade. However, planar wiring for superconducting qubits would limit the system size to around a hundred qubits. Achieving a scalable qubit structure with three-dimensional (3D) wiring that can fully control the qubit in terms of σ_z and σ_x is still a significant challenge. Here, we demonstrate a 4×4 concentric tunable transmon qubit chip measured in a pogo-pin package with vertical wiring. We show that we can apply more than 600μA of dc current through the pogo pins to all the qubits without affecting their coherence time and thermal excitation. Besides, our chip shows quite low σ_z-crosstalk (<5x10^-3), and σ_x-crosstalk (<30dB) with long coherence time (T₁ >200μs at 4GHz, T_2echo >100μs at the sweet point). These key 3D-integration technologies pave the way for tunable qubit-based large-scale superconducting quantum computing and quantum simulation.