Forced Entanglement of Circularly Polarized Photons

The Quantum Zeno effect reveals that a quantum system being continuously observed will have its natural time-evolution suppressed. More generally, the number of states accessible to the system is reduced depending on the type of measurement being performed. It is conceivable, therefore, that one might be able to "force" a group of particles into an entangled quantum state by restricting the system's access to only those states which compose an entangled state of a system. A numerical simulation is performed such that an unentangled pair of photons is evolved into a polarization entangled state. Beginning with one photon each of right and left circular polarization, the pair are sent through a pair of coupled waveguides in separate modes. The coupled waveguides cause the photons to gradually switch between modes with 4 possible states of the system; two in which the photons are in the same mode, bunched states, and two in which they are in opposite modes, unbunched states. Placing diamond configuration 4-level absorbers in the path of both waveguides, bunched states are suppressed so the system only evolves between unbunched states. Appropriate choice of length for the coupled waveguides then leaves the photons in an entangled state at the output.