"When the quantum system contains more than one particle, the superposition principle gives rise to the phenomenon of entanglement. It is now not just a particle interfering with itself—it is a system interfering with itself: an entangled system. Amazingly enough, Erwin Schrödinger himself realized that particles or photons produced in a process that links them together will be entangled, and he actually coined the term entanglement, both in his native German and in English. Schrödinger discovered the possibility of entanglement in 1926, when he did his pioneering work on the new quantum mechanics, but he first used the term entanglement in 1935, in his discussion of the Einstein, Podolsky, and Rosen (EPR) paper."