  Quantum entanglement is the quintessence of quantum information processing
mostly limited to the microscopic regime governed by Heisenberg uncertainty
principle. For practical applications, however, macroscopic entanglement gives
great benefits in both photon loss and sensitivity. Recently, a novel method of
macroscopic entanglement generation has been proposed and demonstrated in a
coupled interferometric system using classical laser light, where superposition
between binary bases in each interferometric system plays a key role. Here, the
function of path superposition applied to independent bipartite classical
systems is analyzed to unveil secrets of quantum features and to convert a
classical system into a quantum system without violating quantum mechanics.
