Quantum measurement-induced antiferromagnetic order and density modulations in ultracold Fermi gases in optical lattices

Abstract

Ultracold atomic systems offer a unique tool for understanding behavior of matter in the quantum degenerate regime, promising studies of a vast range of phenomena covering many disciplines from condensed matter to quantum information and particle physics. Coupling these systems to quantized light fields opens further possibilities of observing delicate effects typical of quantum optics in the context of strongly correlated systems. Measurement backaction is one of the most funda- mental manifestations of quantum mechanics and it is at the core of many famous quantum optics experiments. Here we show that quantum backaction of weak measurement can be used for tailoring long-range correlations of ultracold fermions, realizing quantum states with spatial modulations of the density and magnetization, thus overcoming usual requirement for a strong interatomic interactions. We propose detection schemes for implementing antiferromagnetic states and density waves. We demonstrate that such long-range correlations cannot be realized with local addressing, and they are a consequence of the competition between global but spatially structured backaction of weak quantum measurement and unitary dynamics of fermions.

Feedback-Induced Quantum Phase Transitions Using Weak Measurements

“…[30]. Our approach can be readily applied to many-body settings as S x can represent various many-body variables [63][64][65], not limited to the sum of all spins: e.g., fermion or spin (staggered) magnetization [46,[66][67][68] or combinations of strongly interacting atoms in arrays, as in lattice experiments [44,45]. The feedback term GI(t) has a form of the timedependent operator-valued Rabi frequency rotating the spins (G is the feedback coefficient and I(t) is the control signal).…”

Cavityless self-organization of ultracold atoms due to the feedback-induced phase transition

“…In particular, one can measure light scattered at an angle that does not satisfy the condition (1), which would contain different information about the distribution of the atoms [58][59][60][61] . The feedback-induced maximization of this signal might result in more exotic states of the atomic ensembles, both bosons and fermions 28,29,[62][63][64][65][66][67][68][69][70] . We leave this interesting possibility for future research.…”

Quantum quasi-Zeno dynamics: Transitions mediated by frequent projective measurements near the Zeno regime

“…Whilst being relatively simple both mathematically and conceptually, this regime has previously been largely unexplored, despite the abundance of possibilities for which it lays the foundations. The field of dissipative dynamics, where the interactions between a system and its environment can be exploited to manipulate the dynamics of a system, and to prepare particular states of the system, has seen a lot of interest [25,26,[42][43][44], as has the very related field of using designed measurement as the source of dissipation for quantum system engineering [27,29,[45][46][47]. This work extends these ideas, as by eliminating particular processes at first-order only, whilst preserving them at second-order (or higher), can lead to the emergence of correlated dynamics, as demonstrated here.…”