A process for entangling quantum states of respective quantum systems measures electromagnetic radiation emitted from a first system and from a second system. The two systems are exposed to excitation radiation having a probability per time of producing a photon, and an interference element is coupled to receive photons from the first and second systems. The process further includes measuring a time during which the first and second systems were exposed to the excitation radiation before a photon is detected on either output channel of the interference element and applying an electromagnetic pulse that causes a relative phase shift of a portion of a quantum state of the first and second systems. Parameters of the electromagnetic pulse are selected based on measurements of the electromagnetic radiation from the first and second systems and the time measured.