Grover multiports are higher-dimensional generalizations of beam splitters in which inputs to any of the four ports have an equal probability of exiting at any of the four ports, including the input port. This offers direct access to a greater number (4x4) of degrees of freedom.

We demonstrate that even standard interferometers can obtain novel features when directionally unbiased multi-ports replace traditional beam splitters. It will be shown that the Grover-based counterpart of the conventional Michelson interferometer can substantially (>10x) enhance the phase measurement sensitivity. The Grover-Michelson interferometer demonstrates a tunable intensity-phase slope instead of a traditional fixed Cos^2 profile, thus enabling super-resolution phase measurement while utilizing only linear optical elements and classical states of light.

The two-photon Hong-Ou-Mandel (HOM) effect could be expanded onto a higher-dimensional set of four spatial modes when combining the Grover coin with quantum-correlated two-photon states and coincidence measurements. The original HOM effect only enables photon pairs to exit in two directions in space We introduce a novel quantum photonic state router design that allows controllable redistribution (switching) of quantum states over all four modes using directionally unbiased linear-optical four-ports without post-selection and controllable by changing the phases in the system. By this means, spatial and temporal control of the propagation of the two-photon entangled state through a large network of quantum user nodes (quantum state routing) can be achieved.

Prof. Alexander Sergienko (e-mail: alexserg@bu.edu) holds joint appointments in the Department of Electrical and Computer Engineering, in the Photonics Center, and the Department of Physics at Boston University since 1996.

His research interests cover quantum information processing, including quantum simulation, computing, and communications, quantum networking, quantum imaging, and the development of novel ultra-precise optical measurement and characterization techniques (quantum metrology and sensing) based on using non-classical states of light. He pioneered the experimental development of practical quantum measurement and quantum imaging techniques with entangled photon states in the 90s.

Prof. Sergienko has published over 150 research journal papers and 330 conference presentations. He holds six patents in experimental quantum optics and entanglement manipulation. He is the editor of "Quantum Communications and Cryptography" (CRC/Taylor & Francis, 2006) and co-author of “Quantum Metrology, Imaging, and Communication" (Springer, 2017). He is an Associate Editor for Physical Review Letters (APS) and Journal of Optics (IOP). He is a Fellow of the Optical Society of America and a member of the APS, IEEE, and SPIE.