Photon: toy, tool or mystery?

Although the concept of a light particle has been introduced more than a hundred years ago, it is only now that the technology has reached the level enabling us to generate single photons and experiment with them. Such experiments reveal numerous paradoxes associated with the deeply nonclassical nature of the photon and thus help us understand the very essence of quantum mechanics. Furthermore, the photon can play a role of an information bit in the quantum computer, a hypothetical device capable of solving certain tasks much faster than its classical counterpart.