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Although light is the main tool in quantum gas physics, its quantumness is often neglected. We show that elevating light to a quantum variable leads to a plethora of novel many-body phenomena, unobtainable in classical optical setups. First, we prove that the quantum backaction of a weak global measurement can efficiently compete with standard short-range processes in a strongly correlated system (ultracold bosons or fermions in an optical lattice), leading to novel phenomena. We demonstrate generation of the multimode generalizations of Schroedinger cat and NOON states, nonlocal quantum Zeno dynamics, and non-Hermitian processes without the need of postselection. For fermions, we show the measurement-induced antiferromagnetic states, as well as the protection and break-up of strongly interacting fermion pairs. The backaction results in the generation of genuinely multipartite entangled modes of matter waves, which show non-Gaussian properties beyond quantum optical analogues. Second, trapping quantum gases inside a high-Q cavity, creates a paradigm of quantum optical lattices. We demonstrate the emergence of novel many-body phases: delocalized dimers, trimers, etc. of matter waves, even beyond the density orders such as density waves and supersolids. We show that cavity QED of strongly correlated systems can efficiently simulate systems with short- and long-range interactions, while still profiting from the collective enhancement of the light-matter interaction.

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Igor Mekhov, Oxford University
Seminar room 0.03, ETP
Contact: Philipp Strack