State-Dependent Quantum Copying and the limits of the No-Cloning Theorem

Abstract: In this work, we examine the physical process of stimulated emission as a model for state-dependent quantum copying. We explore how a quantum state, for instance, a photon polarization, can be cloned through light-matter interactions when the ancillary system, such as an excited atom, effectively encodes prior information about the quantum state. This process, while resembling quantum cloning, adheres to the no-cloning theorem due to its state-dependent and non-universal nature. We clarify the distinction between universal cloning and conditional copying, and demonstrate that stimulated emission offers a concrete physical realization of state-dependent quantum copying.