The Quantum Socket and DemuXYZ-Based Gates with Superconducting Qubits

Building large-scale superconducting quantum computers requires two complimentary elements: scalable wiring techniques and multiplex architectures. In our previous work [Béjanin et al., Phys. Rev. Applied 6, 044010 (2016)], we have introduced and characterized a truly vertical interconnect named the quantum socket. In this paper, we exercise the quantum socket using high-coherence flux-tunable Xmon transmon qubits. In particular, we test potential qubit heating and one-qubit gate performance. We observe no heating effects and time-stable gate fidelities in excess of 99.9%. We then propose and experimentally characterize a demultiplexed gate technique based on flux pulses and a common continuous drive signal: DemuXYZ. We discuss DemuXYZ's working principle, show its operation, and perform quantum process tomography on a selection of one-qubit gates to confirm proper operation. We obtain fidelities around 93% likely limited by flux-pulse imperfections. We finally discuss future solutions for wiring integration as well as improvements to the DemuXYZ technique.