Quantum correlations at infinite temperature: The dynamical Nagaoka effect

The interplay of quantum correlations and thermal decoherence is key to understanding the fundamental properties of many-body systems. Coherence is usually easily destroyed by interaction with the environment and local fluctuations inherent to thermal ensembles. Hence experimental demonstrations of many-body quantum correlations rely on cooling the system close to its ground state or pumping it into a well-defined quantum state. Here, the authors instead show how quantum correlations can arise in the opposite limit of an infinite temperature. Motivated by recent experiments with ultracold atoms in optical lattices, they study the dynamics of a hole created in a fermionic or bosonic Mott state in the atomic limit. They demonstrate that the propagating hole entangles the surrounding spins leading to sizable and lasting dynamical spin correlations. In the absence of interactions, these correlations arise solely due to quantum interference. Furthermore, they are both ferromagnetic and antiferromagnetic, in contrast to the equilibrium Nagaoka effect.