Army Researchers and Dr. Mikkel Heuck and Prof. Dirk Englund of the Massachusetts Institute of Technology have demonstrated the feasibility of a quantum logic gate comprised of photonic circuits and optical crystals.

Researchers can engineer cavities in the crystals that temporarily trap photons inside. Through this method, the quantum system can establish two different possible states that a qubit can hold: a cavity with a photon (on) and a cavity without a photon (off). These qubits can then form quantum logic gates, which create the framework for the strange states.

Physical Review Letters – Controlled-Phase Gate Using Dynamically Coupled Cavities and Optical Nonlinearities

ABSTRACT
We show that relatively simple integrated photonic circuits have the potential to realize a high fidelity deterministic controlled-phase gate between photonic qubits using bulk optical nonlinearities.