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 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.

Arm Qubit Design: Coherence and Coupling Architecture

Single-qubit gate infidelities remain below 1×10^-5 within simulations of the new “arm qubit” design, a level of precision enabled by the architecture’s focus on both coupling strength and coherence preservation. This performance surpasses existing experimental benchmarks, suggesting a pathway toward more reliable quantum computations and reduced error correction overhead. The qubit’s design utilizes capacitive coupling exclusively, streamlining fabrication and scalability compared to approaches requiring multiple material layers or complex control schemes.