Continuous operations on non-Markovian processes

Abstract

Continuous measurements are central to quantum control and sensing, yet lack a model-independent operational description that can be applied to arbitrary non-Markovian processes without specifying a microscopic measurement model. Existing multi-time frameworks, such as process matrices, allow for an arbitrary sequence of operations to be applied on a general process, but are restricted to interventions at discrete times and cannot represent measurements of finite duration. We introduce a continuous-time extension of multi-time quantum processes based on process and operation functionals, which generalize the Feynman-Vernon influence functional and yield a continuous Born rule that cleanly separates processes from operations. This framework provides a consistent representation of non-Markovian dynamics under continuous monitoring and leads to a natural definition of Markovianity in continuous time. We illustrate the formalism by analyzing continuous measurements in a generalized Caldeira-Leggett model, demonstrating its applicability to realistic non-Markovian scenarios.