ABSTRACT
This chapter discusses some of the guiding principles on systems based optical photons from lasers. Optical photons constitute suitable physical system to represent a qubit. The orthodox view of quantum mechanics is that after the measurement the system collapses to a wave function that gives the result of measurement of the physical property. But according to the realistic view of Einstein, Podolsky and Rosen (EPR), the system has the property even before the measurement since it gives a certain result in the measurement. Hence according to EPR paradox quantum mechanics is an incomplete theory, since there is some external information that is necessary for interpretation of physical reality. In quantum information science the qubit levels are usually denoted as |0> and |1>. An important application of quantum entanglement is quantum teleportation or quantum information transfer. In this process, a quantum state is transferred from one place to another that may be wide apart.
