A Demonstration of Multifloating Superconducting Qubits on a 3-D 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 3-D flip-chip platform. A major focus during qubit design is addressing coherence challenges caused by two-level system (TLS) losses, particularly from surface interfaces. TLS losses at 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 3-D 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 measurement of the qubit frequency.