It was the photon that started the world of quantum in 1905, when Einstein took seriously a concept introduced by Planck and such proposed the laser. Soon, photons seen as exchange particles for the electromagnetic force triggered QED and Feynman to postulate quantum machines. Discovery of photon’s quantum statistical properties led to the understanding and practical technical use of quantum correlations, entanglement and quantum coherence. The photon is the most accessible handle for quantum information. It is used to set and read-out qubits, quantum sensors, etc. It is the only carrier to allow large distance transport of quantum information. Tamed photons are the key enabling tool for Quantum 2.0 and today’s laser are an incarnation thereof, as basis for QT applications we can only start to anticipate.
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