Restoring polarization entanglement from solid-state photon sources by time-dependent photonic control
Quantum states of light are central resources for quantum communication, networking, and photonic information processing. In many quantum emitters, coherent internal dynamics arising from intrinsic or field-induced level splittings imprint a deterministic, time-dependent phase on the emitted light. When emission times are stochastic and detector timing resolution is finite, this phase evolution becomes effectively unresolved, suppressing observable entanglement. Here, we demonstrate a photonic-compensation protocol that removes this emitter-induced phase evolution directly in the photonic domain. Rather than modifying the emitter, we apply synchronized, time-dependent coherent operations to the emitted photons that reverse the accumulated phase independently of the emission time. Using exciton fine-structure splitting in a semiconductor quantum dot as a model system, we implement dynamic phase modulation and perform time-resolved two-photon polarization tomography. We show that this restores a stationary two-photon polarization state and recovers polarization entanglement without temporal post-selection and independently of detector timing resolution. Our approach provides a scalable route to robust solid-state entangled-photon sources and, more broadly, establishes a strategy for removing the imprint of coherent emitter dynamics on photonic entanglement in integrated platforms.