Non-Markovian memory strength bounds quantum process recoverability

Generic non-Markovian quantum processes have infinitely long memory, implying an exact description that grows exponentially in complexity with observation time. Here, we present a finite memory ansatz approximates (or recovers) the true process errors bounded by strength of memory. The introduced is operational quantity and depends on way probed. Remarkably, recovery error smallest over all possible probing methods. This allows for unambiguous efficient phenomena, enabling compression techniques pivotal to near-term technologies. We highlight implications our results analyzing exactly solvable model show truncation even highly regime.