Nonclassical Phenomena in Multiphoton Interferometry: More Stringent Tests Against Local Realism

Abstract

The thesis is divided into three parts. In the first part a new theoretical analysis of interferometric experiments by Alley-Shih, Ou-Mandel and the entanglement swapping experiment is performed. It is shown that the double- and single-photon distinguishability is not necessary for the experiments to be genuine tests against local realism. In the second part, basing on simple geometrical properties of Hilbert space, new, stronger Bell inequalities for M qubits in a maximally entangled state are derived. Application of the same method to two maximally entangled qubits yields an inequality for all possible positions of the local measuring apparatus. Finally, the series of the Greenberger-Horne- Zeilinger paradoxes for M maximally entangled quNits observed via symmetric unbiased 2N ports is derived. The last part of the thesis is devoted to the numerical approach to the Bell theorem. The necessary and sufficient conditions for the violation of local realism in the case of two and three maximally entangled qubits, on which each observer performs up to 10 (two qubits) and up to 5 (three qubits) local measurements, are shown. It is also numerically shown that in the case of two maximally entangled quNits (3 < N < 9) a properly defined magnitude of violation increases with N. In both cases the approach neither involves any simplifications, or additional assumptions, nor does it utilise any symmetries of the problem.