Universal quantum operations and ancilla-based read-out for tweezer clocks.

Abstract

Enhancing the precision of measurements by harnessing entanglement is a long-sought goal in quantum metrology^1,2. Yet attaining the best sensitivity allowed by quantum theory in the presence of noise is an outstanding challenge, requiring optimal probe-state generation and read-out strategies^3-7. Neutral-atom optical clocks⁸, which are the leading systems for measuring time, have shown recent progress in terms of entanglement generation^9-11 but at present lack the control capabilities for realizing such schemes. Here we show universal quantum operations and ancilla-based read-out for ultranarrow optical transitions of neutral atoms. Our demonstration in a tweezer clock platform^9,12-16 enables a circuit-based approach to quantum metrology with neutral-atom optical clocks. To this end, we demonstrate two-qubit entangling gates with 99.62(3)% fidelity-averaged over symmetric input states-through Rydberg interactions^15,17,18 and dynamical connectivity¹⁹ for optical clock qubits, which we combine with local addressing¹⁶ to implement universally programmable quantum circuits. Using this approach, we generate a near-optimal entangled probe state^1,4, a cascade of Greenberger-Horne-Zeilinger states of different sizes, and perform a dual-quadrature⁵ Greenberger-Horne-Zeilinger read-out. We also show repeated fast phase detection with non-destructive conditional reset of clock qubits and minimal dead time between repetitions by implementing ancilla-based quantum logic spectroscopy²⁰ for neutral atoms. Finally, we extend this to multi-qubit parity checks and measurement-based, heralded, Bell-state preparation^21-24. Our work lays the foundation for hybrid processor-clock devices with neutral atoms and more generally points to a future of practical applications for quantum processors linked with quantum sensors²⁵.