A Demonstration of Multi-Floating Superconducting Qubits on a 3D Flip-Chip Platform with TLS Loss Mitigation via Apertures

Flip-chip platforms are among the most promising approaches for scaling up superconducting qubits in quantum computing. This work presents the design, modeling, and analysis of floating transmon qubits implemented on a 3D flip-chip platform. A major focus during qubit design is addressing coherence challenges caused by TLS (two-level system) losses, particularly from surface interfaces. TLS losses from the metal-air (MA) interface are mitigated by introducing apertures beneath the qubit pads. The aperture size is optimized to balance two key factors: minimizing total TLS loss and ensuring sufficient coupling strength between the transmon and resonator. Subsequently, A packaged 3D chip comprising 24 floating transmons is demonstrated. The transmission spectrum is measured, with all readout resonators successfully located at their designated positions on the spectrum. Two-tone spectroscopy is demonstrated, enabling precise measuring the qubit frequency.