The Compact High-Coherence Superconducting Qubit: Realization via Meander-Shaped Capacitor

Scalable superconducting qubit architectures demand qubits with long coherence times—a critical prerequisite for developing practical quantum computers. To achieve a compact circuit footprint, we have designed a superconducting qubit featuring a meander-structured coplanar waveguide capacitor, termed the “Smon.” Numerical simulations of the electric field distribution demonstrate that the Smon exhibits a significantly lower energy participation ratio (EPR) than both Xmon qubits and conventional rectangular planar transmon qubits. For an in situ comparison between Smons and conventional rectangular planar transmons, we propose a two-dimensional (2D) hybrid qubit array test structure. The capacitor electrodes of the devices are fabricated using tantalum. Measurements of the Smon’s coherence properties yield an energy relaxation time ( T 1 ) ranging from 30 to 359 µs and a dephasing time ( T 2 ) between 18 and 20 µs. These results confirm that superconducting quantum circuits with enhanced integration density and long coherence times are experimentally feasible, thereby offering a viable pathway toward high-performance large-scale superconducting quantum computers.