Unimon qubit

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, ω 01 /(2 π ), and increased anharmonicity α /(2 π ) at the optimal operation point, yielding, for example, 99.9% and 99.8% fidelity for 13 ns single-qubit gates on two qubits with ( ω 01 , α ) = (4.49 GHz, 434 MHz) × 2 π and (3.55 GHz, 744 MHz) × 2 π , 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. While transmon is the most widely used superconducting qubit, the search for alternative qubit designs with improved characteristic is ongoing. Hyyppä et al. demonstrate a novel superconducting qubit, the unimon, that combines high anharmonicity and protection against low-frequency charge noise and flux noise.