Quantum Optics 2 - Two photons and more

"Quantum Optics 1, Single photons", allowed learners to be introduced to the basic principles of light quantization, and to the standard formalism of Quantum Optics. All the examples were taken in single photons phenomena, including applications to quantum technologies. In the same spirit, "Quantum Optics 2, Two photons and more", will allow learners to use the Quantum Optics formalism to describe entangled photon, a unique feature at the root of the second quantum revolution and its applications to quantum technologies. Learners will also discover how the Quantum Optics formalism allows one to describe classical light, either coherent such as laser light, or incoherent such as thermal radiation. Using a many photons description, it is possible to derive the so-called Standard Quantum Limit (SQL), which applies to classical light, and to understand how new kinds of quantum states of light, such as squeezed states of light, allow one to beat the SQL, one of the achievements of quantum metrology. Several examples of Quantum Technologies based on entangled photons will be presented, firstly in quantum communication, in particular Quantum Teleportation and Quantum Cryptography. Quantum Computing and Quantum Simulation will also be presented, including some insights into the recently proposed Noisy Intermediate Scale Quantum (NISQ) computing, which raises a serious hope to demonstrate, in a near future, the actively searched quantum advantage, ie, the possibility to effect calculations exponentially faster than with classical computers.