Imprinting of the dynamics of a single electron spin on a coherent state

The interaction of quantum objects is of fundamental nature in the exploration of the quantum properties of the world and for a wide range of quantum technologies. Specifically, the interactions between a photon or a coherent state and a quantum emitter are among the most well-studied areas. The interactions between two qubits are generally simplified into two quantum objects in static well defined states. In this work we explore a fundamentally new dynamic type of spin-photon interaction. We show the imprinting of the dynamics from a single electron spin in the ground state of a quantum dot. A quantum modulation of the output phase (either 0 or π but no values in between) is observed, forming a novel quantum state of light that cannot be described classically. This state of light can directly witness the underlying dynamics of a spin in a quantum emitter.