Entanglement is a key feature of quantum mechanics. Usually, it is discussed in the context of two subsystems at a given time. A natural question is whether the notion of entanglement can be extended to subsystems at different times. I will present a novel family of such entanglement measures. Their key property is providing upper bounds to time-separated correlation functions, akin to the bound on spatially separated correlators in terms of the mutual information. For relativistic quantum field theories our definition agrees with the analytic continuation from space-like to time-likes separated regions. I will discuss the measurement protocols and report explicit computations for Ising chain, free fermions, 1+1 dimensional conformal field theories and holographic theories.
This is a work in progress with Zofia Adamska and John Preskill
