Decades of research into the foundational aspects of quantum mechanics — started with the Einstein-Podolsky-Rosen (EPR) paradox on entanglement and non-locality — have brought us a radically new way of thinking about physical systems: the latter can be now viewed as hosts of quantum information encoded in quantum superpositions, and as potential resources for novel quantum technologies. A central question is how to assess the non-classical nature of quantum states, namely their characterization as coherent superpositions featuring non-local correlations. This question becomes particularly intriguing and intricate when moving to many-body systems: the exponential growth of quantum information with the system size makes many-body tomography simply inaccessible, and strategies for a scalable assessment of quantumness need to be devised. This endeavor has obviously a foundational aspect, ultimately aiming at an exploration of the mysterious quantum-classical boundary; but it has also immediate bonuses, since assessing quantumness of many-body states can translate into probing their potential use as resources for quantum information tasks.

In this talk I will survey our recent activities in characterizing the quantum nature of large-scale, mixed many-body states in its various forms of increasing non-classicality, namely: quantum correlations at large; entanglement; EPR correlations; and Bell correlations. I will discuss criteria inspired by quantum information, quantum statistical physics and quantum metrology, and specifically apply them to many-body states in the vicinity of a quantum critical point, where critical quantum fluctuations lead to the strongest forms of quantum correlations known at equilibrium. Such states are readily accessible to quantum simulators for discrete variables (qubits encoded in superconducting circuits, trapped ions, Rydberg atoms, etc.) as well as continuous variables (lattice bosons). Making use of advanced numerics, we can reconstruct the “non-classicality phase diagram” (indicating the equilibrium regimes at finite temperature in which the various forms of quantum correlations can be detected) for paradigmatic models of quantum simulation -- such as the quantum Ising model and the Bose-Hubbard model. In the specific case of discrete variables, this allows us to assess the metrological utility of the equilibrium quantum many-body state, viewed as input state of an interferometer.


Seminar, April 16, 2019, 12:00. ICFO’s Seminar Room

Hosted by Maciej Lewenstein