Progress towards variationally optimized quantum circuits in an optical clock

Leveraging entanglement in order to reach sensitivities beyond classical limits is a central goal of quantum-enhanced metrology [1]. Recent theoretical work suggests that variationally optimized quantum circuits can yield significant metrological advantages [2]. Previous demonstrations of spin squeezing with Rydberg interactions on our strontium atom array optical clock were limited by the finite range of the interactions [3]. The variational approach of combining simple quantum operations, like global single qubit rotations and dynamics under short-range Ising interactions, into novel entangling and decoding sequences can optimize the generation of entanglement across the array and enable measurement in an entangled basis. These useful circuits are obtained by varying the constituent quantum operations and using the sensitivity as the cost function. We report progress towards implementing variationally optimized circuits on our apparatus. We aim to first implement sequences obtained from running variational optimization on numeric simulations to benchmark physical performance, with the ultimate goal of performing the optimization procedure directly on our quantum hardware. 

References:

[1] L. Pezze et al. Quantum metrology with nonclassical states of atomic ensembles, Rev. Mod. Phys. 90, 035005 (2018).

[2] R. Kaubruegger et al.. Quantum Variational Optimization of Ramsey Interferometry and Atomic Clocks, Phys. Rev. X 11, 041045 (2021).

[3] Eckner, W.J. et al. Realizing spin squeezing with Rydberg interactions in an optical clock. Nature 621, 734–739 (2023).