Multipartite entangled states in dipolar quantum simulators

The scalable production of multipartite entangled states in ensembles of qubits is a fundamental function of quantum devices, as such states are an essential resource both for fundamental studies on entanglement, as well as for applied tasks. Here we focus on the $U(1)$ symmetric Hamiltonians for qubits with dipolar interactions -- a model realized in several state-of-the-art quantum simulation platforms for lattice spin models, including Rydberg-atom arrays with resonant interactions. Making use of exact and variational simulations, we theoretically show that the non-equilibrium dynamics generated by this lattice spin Hamiltonian shares fundamental features with that of the one-axis-twisting model, namely the simplest interacting collective-spin model with $U(1)$ symmetry. The evolution governed by the dipolar Hamiltonian generates a cascade of multipartite entangled states -- spin-squeezed states, Schr\"odinger's cat states, and multi-component superpositions of coherent spin states. Investigating systems with up to $N=144$ qubits, we observe full scalability of the entanglement features of these states directly related to metrology, namely scalable spin squeezing at an evolution time ${\cal O}(N^{1/3})$; and Heisenberg scaling of sensitivity of the spin parity to global rotations for cat states reached at times ${\cal O}(N)$. Our results suggest that the native Hamiltonian dynamics of state-of-the-art quantum simulation platforms, such as Rydberg-atom arrays, can act as a robust source of multipartite entanglement.
Comment: 4.5 + 3.5 pages; 5 + 5 figures