New MIT qubit design consists of two strongly coupled modes: one for data storage and one for coupling, allowing faster, higher-fidelity entangling gates and readout

Jeremy B. Kline and colleagues at the Massachusetts Institute of Technology have designed a superconducting qubit achieving microwave-only CZ gates with an infidelity of just 1×10⁻⁵ in just 17 nanoseconds. This new "arm qubit" utilizes two strongly coupled modes, one for data storage and one for coupling, to enable faster, higher-fidelity operations and readout. Simulations demonstrate a Purcell-limited lifetime of 167 milliseconds without requiring a Purcell filter, a component typically needed to extend qubit coherence. These fidelities, achieved through capacitive coupling, position the arm qubit as a promising component for scalable, fault-tolerant quantum computers. Single-qubit gate infidelities remain below 1×10⁻⁵ within simulations of the new "arm qubit" design, a level of…