High-fidelity gates and mid-circuit erasure conversion in an atomic qubit.

The development of scalable, high-fidelity qubits is a key challenge in quantum information science. Neutral atom qubits have progressed rapidly in recent years, demonstrating programmable processors 1,2 and quantum simulators with scaling to hundreds of atoms 3,4 . Exploring new atomic species, such as alkaline earth atoms 5-7 , or combining multiple species 8 can provide new paths to improving coherence, control and scalability. For example, for eventual application in quantum error correction, it is advantageous to realize qubits with structured error models, such as biased Pauli errors 9 or conversion of errors into detectable erasures 10 . Here we demonstrate a new neutral atom qubit using the nuclear spin of a long-lived metastable state in 171 Yb. The long coherence time and fast excitation to the Rydberg state allow one- and two-qubit gates with fidelities of 0.9990(1) and 0.980(1), respectively. Importantly, a large fraction of all gate errors result in decays out of the qubit subspace to the ground state. By performing fast, mid-circuit detection of these errors, we convert them into erasure errors; during detection, the induced error probability on qubits remaining in the computational space is less than 10 -5 . This work establishes metastable 171 Yb as a promising platform for realizing fault-tolerant quantum computing.