Investigation Of Directional And Directionally-Unbiased Devices In Linear Optics For Quantum Walk Applications

The optical beam splitter is one of the main building blocks in photonics-based quantum information processing. Traditionally, beam splitters are used in feed-forward configurations that reflect their natural directional-bias, meaning a photon cannot leave the scattering element through the entrance port. However, this directional-bias constraint can be circumvented by designing new linear-optical configurations that include mirrors in addition to the beam splitter. This directionality removal restores a full symmetry in the scattering element and allows the input photon to leave the system also from the input port. Such a system can be seen as a scattering center, enabling execution of quantum walks on rather complex optical graph networks with great savings in hardware resources when compared with existing approaches utilizing directionally-biased devices. The directionally-unbiased configuration can be realized using different optical systems. Analysis of some originally directional optical devices and the basic principles of their conversion into directionally-unbiased systems form the base of this paper. Several quantum walk procedures executed on graph networks constructed using directionally-unbiased nodes are discussed.