@article{13404,
  author = {Alec Cao and William Eckner and Theodor Yelin and Aaron Young and Sven Jandura and Lingfeng Yan and Kyungtae Kim and Guido Pupillo and Jun Ye and Nelson Oppong and Adam Kaufman},
  title = {Multi-qubit gates and  Schrödinger cat  states in an optical clock},
  abstract = {<p>Many-particle entanglement is a key resource for achieving the fundamental precision limits of a quantum sensor. Optical atomic clocks, the current state-of-the-art in frequency precision, are a rapidly emerging area of focus for entanglement-enhanced metrology. Augmenting tweezer-based clocks featuring microscopic control and detection with the high-fidelity entangling gates developed for atom-array information processing offers a promising route towards leveraging highly entangled quantum states for improved optical clocks. Here we develop and employ a family of multi-qubit Rydberg gates to generate 'Schrödinger cat' states of the Greenberger-Horne-Zeilinger (GHZ) type with up to 9 optical clock qubits in a programmable atom array. In an atom-laser comparison at sufficiently short dark times, we demonstrate a fractional frequency instability below the standard quantum limit using GHZ states of up to 4 qubits. A key challenge to improving the optimal achievable clock precision with GHZ states is their reduced dynamic range. Towards overcoming this hurdle, we simultaneously prepare a cascade of varying-size GHZ states to perform unambiguous phase estimation over an extended interval. These results demonstrate key building blocks for approaching Heisenberg-limited scaling of optical atomic clock precision.</p>
},
  year = {2024},
  journal = {Submitted},
  url = {https://arxiv.org/abs/2402.16289},
}