Digital Quantum Algorithms for Generating and Utilizing Spin Squeezed States

Spin squeezed states (SSSs) are conventionally viewed as analog resources for quantum metrology. Here we develop algorithms to efficiently generate and exploit SSSs on a digital quantum computer. We introduce an adaptive local-circuit protocol that prepares SSSs with squeezing parameter $\xi$ in depth $\mathrm{O}(\log 1\mathrm{/}\xi )$, yielding an exponential improvement over non-adaptive approaches. We prove that this depth is optimal for permutation symmetric SSSs by deriving a matching lower bound on entanglement entropy. We further leverage the squeezing paradigm to deterministically prepare the Dicke states using asymptotically fewer resources than prior methods. Remarkably, classical simulations of our preparation protocols under realistic noise models predicts a metrological gain of 4.2 dB beyond the standard quantum limit with 55 superconducting qubits in total including ancillae. Our work paves the way for performing quantum metrology on near-term digital quantum devices.