Single-photon interferometry has been used to simulate quantum computations. Its use has been limited to studying few-bit applications due to rapid growth in physical size with numbers of bits. We propose a hybrid approach that employs n photons, each having L degrees of freedom yielding Ln basis states. The photons are entangled via a quantum nondemolition measurement. This approach introduces the essential element of quantum computing, that is, entanglement into the interferometry. Using these techniques, we demonstrate a controlled-NOT gate and a Grover's search circuit. These ideas are also applicable to the study of nonlocal correlations in many dimensions.
J. C. Howell and J. A. Yeazell, Quantum Computation Through Entangling Single Photons in Multipath Interferometers, Phys. Rev. Lett. 85(1), 198. https://doi.org/10.1103/PhysRevLett.85.198
American Physical Society