Title: "Diagnosing quantum chaos in many-body systems using entanglement"

Abstract: Classical chaotic systems exhibit exponentially diverging trajectories
due to small differences in their initial state. The analogous
diagnostic in quantum many-body systems is an exponential growth of
out-of-time-ordered correlation functions (OTOCs). These quantities can
be computed for various models, but their experimental study requires
the ability to evolve quantum states backward in time, similar to the
canonical Loschmidt echo measurement. In some simple systems, backward
time evolution can be achieved by reversing the sign of the Hamiltonian;
however in most interacting many-body systems, this is not a viable
option. In this talk I will discuss a new family of protocols for OTOC
measurement that do not require backward time evolution. Instead, they
rely on ordinary time-ordered measurements performed in an entangled
state formed between two identical copies of the system. I will show
that, remarkably, in this situation the Lyapunov chaos exponent λ can be
extracted from the measurement of an ordinary two-point correlation
function under equilibrium conditions.