All counterintuitive and mysterious phenomena exhibited by the quantum theory are linked with the concept of quantum coherence in one way or the other. The best available tool to explicitly explore the in depth meaning of the quantum coherence is to utilize single-particle quantum interference under any preselected experimental scenario. Present thesis employs the themes of Delayed-Choice Quantum Eraser (DCQE) under single and double tag settings as well as the ideology of complementarity tested through Atomic Mach-Zehnder-Bragg interferometer for the purpose. For the DCQE case, our results clearly demonstrate that coherence and hence the interference fringes that get lost due to coupling with the tag ancilla can not only be retrieved back but strangely enough can also be tuned in a delayed-choice manner much later than the due data recording. This delayed-choice adjustability of the fringes shed out many controversies surrounding the quantum eraser along with the conception of the time in the quantum theory, meanings of the state vector reduction, measurement, information and the entropy as well as raises questions about the Ψ- ontic models. The second proposal suggests that quantum coherence apparently seems to lie beyond our classical space-time structure. Whereas the proposal based on atom interferometer with final beam splitter being quantum mechanical i.e. in superposition of being absent and present simultaneously, was used to observe both the wave and particle aspects under a single experimental setting, as suggested recently by Ionicioiu et.al. [Phys. Rev. Lett. 107, 230406 (2011)], and thus questioned the universality of the Bohr''s conjecture. We demonstrated it in a most realistic scenario based on an atomic interferometer with the final beam splitter taken as a high-Q cavity containing the field superposition of zero and one photon. The setup operates through first order off-resonant Atomic Bragg diffraction from the cavity fields with atom''s particle (wave) nature marked through the absence (presence) of a photon in the final cavity and explicitly exhibit wave-particle morphic behavior versus interaction variables. The thesis concludes with demonstration of experimental feasibility of the presented proposals and highlights future directions with a comprehensive philosophical discussion.