Superconducting qubits seem promising for useful quantum computers, but the currently wide-spread qubit designs and techniques do not yet provide high enough performance. Here, we introduce a superconducting-qubit type, the unimon, which combines the desired properties of increased anharmonicity, full insensitivity to dc charge noise, reduced sensitivity to flux noise, and a simple structure consisting only of a single Josephson junction in a resonator. In agreement with our quantum models, we measure the qubit frequency, ω₀₁/(2π), and increased anharmonicity α/(2π) at the optimal operation point, yielding, for example, 99.9% and 99.8% fidelity for 13 ns single-qubit gates on two qubits with (ω₀₁, α) = (4.49 GHz, 434 MHz) × 2π and (3.55 GHz, 744 MHz) × 2π, respectively. The energy relaxation seems to be dominated by dielectric losses. Thus, improvements of the design, materials, and gate time may promote the unimon to break the 99.99% fidelity target for efficient quantum error correction and possible useful quantum advantage with noisy systems.

超导量子位对于有用的量子计算机似乎很有希望，但目前广泛使用的量子位设计和技术尚未提供足够高的性能。在这里，我们介绍了一种超导量子位类型unimon ，它结合了所需的特性，即增加的非谐波性、对直流电荷噪声完全不敏感、对通量噪声的敏感性降低以及仅由谐振器中的单个约瑟夫森结组成的简单结构。与我们的量子模型一致，我们测量了最佳操作点处的量子位频率ω ₀₁ /(2 π ) 和增加的非谐性α /(2 π )，例如，13 ns 的保真度为 99.9% 和 99.8%两个量子位上的单量子位门，分别为 ( ω ₀₁ , α ) = (4.49 GHz, 434 MHz) × 2 π和 (3.55 GHz, 744 MHz) × 2 π 。能量弛豫似乎主要由介电损耗决定。因此，设计、材料和门时间的改进可能会促进 Unimon 突破 99.99% 的保真度目标，实现有效的量子纠错，并可能在噪声系统中发挥有用的量子优势。