Quantum simulators as quantum sensors: quantum entanglement and correlations from strongly interacting phases of matter

Quantum simulation aims at the controlled realization of highly entangled states of quantum many-body systems, with the scientific as well as technological bonus that such states may be potentially intractable on a classical... [ view full abstract ]

Quantum simulation aims at the controlled realization of highly entangled states of quantum many-body systems, with the scientific as well as technological bonus that such states may be potentially intractable on a classical computer. Here we theoretically propose to view the many-body entanglement that a quantum simulator can naturally produce in equilibrium states as a resource, establishing a link with quantum metrology. We shall discuss such a link with two concrete examples. The entanglement developing at and around the quantum critical point of quantum Ising models (naturally realized by quantum simulators based on trapped ions, Rydberg atoms or superconducting circuits) is found to be of obvious metrological utility. Indeed such entanglement is witnessed by extreme spin squeezing, overcoming the scaling of the standard quantum limit for short-range interactions in dimensions d=3, or with long-range interactions in all dimensions [1]. In the case of ultracold bosonic atoms loaded in an optical lattice, realizing the Bose-Hubbard model, interparticle interactions generate strong entanglement in momentum space. Such entanglement is found to evolve from two-mode squeezing mediated by the condensate in the weakly interacting regime, to massive many-mode entanglement upon approaching the quantum phase transition to the Mott-insulating phase.  

[1] I. Frérot and T. Roscilde, Quantum critical metrology, arXiv:1707.08804 (Phys. Rev. Lett., in press)