  Out-of-time-ordered correlation functions (OTOCs) play a crucial role in the
study of thermalization, entanglement, and quantum chaos, as they quantify the
scrambling of quantum information due to complex interactions. As a consequence
of their out-of-time-ordered nature, OTOCs are difficult to measure
experimentally. Here we propose an OTOC measurement protocol that does not rely
on the reversal of time evolution and is easy to implement in a range of
experimental settings. The protocol accounts for both pure and mixed initial
states, and is applicable to systems that interact with environmental degrees
of freedom. We demonstrate the application of our protocol by the
characterization of scrambling in a periodically-driven spin that exhibits
quantum chaos.
