Happy centenary, photon.

One hundred years ago Albert Einstein introduced the concept of the photon. Although in the early years after 1905 the evidence for the quantum nature of light was not compelling, modern experiments--especially those using photon pairs--have beautifully confirmed its corpuscular character. Research on the quantum properties of light (quantum optics) triggered the evolution of the whole field of quantum information processing, which now promises new technology, such as quantum cryptography and even quantum computers.