Classical Coherent States Based Quantum Information Processing and Quantum Computing Analogs

It has been recently demonstrated by Bellini's group that macroscopic states, such as coherent states, can be entangled by the delocalized photon addition. Deymier's group has shown that phase bits (phi-bits) gates implemented by employing the topological acoustics (TA) principles can be used to implement the TA-based quantum computing analogs. This motivates us to revisit our previous papers where we have already described how to implement the universal quantum gates in integrated optics using optical hybrid, directional coupler, Mach-Zehnder interferometer, and periodically poled lithium niobate (PPLN) waveguides, but in a different context. In this paper, we describe how to implement the universal set of quantum gates classical analogs in integrated optics by employing classical polarization states derived from classical coherent states. The main problem for integrated optics implementation on a single photon level has been to implement the controlled-phase gate because the existing optical nonlinear devices where incapable of introducing the ${\pi }$ rad phase shift on a single photon level through the Kerr effect, which is not a problem at all when the classical polarization states are used instead. We also describe how to implement quantum qudit analogs based on orbital angular momentum (OAM) states and corresponding qudit gates. To highlight the importance of the proposed concepts, we experimentally demonstrate the controlled-phase gate analog operation between the classical coherent states.