Spectroscopy and modeling of ^171Yb Rydberg states for high-fidelity two-qubit gates

We present multichannel quantum defect (MQDT) models for highly excited ^174Yb and ^171Yb Rydberg states with L ≤ 2. The models are developed using a combination of existing literature data and new, high-precision laser and microwave spectroscopy in an atomic beam, and validated by detailed comparison with experimentally measured Stark shifts and magnetic moments. We then use these models to compute interaction potentials between two Yb atoms, and find excellent agreement with direct measurements in an optical tweezer array. From the computed interaction potential, we identify an anomalous Förster resonance that likely degraded the fidelity of previous entangling gates in ^171Yb using F=3/2 Rydberg states. We then identify a more suitable F=1/2 state, and achieve a state-of-the-art controlled-Z gate fidelity of ℱ=0.994(1), with the remaining error fully explained by known sources. This work establishes a solid foundation for the continued development quantum computing, simulation and entanglement-enhanced metrology with Yb neutral atom arrays.