Welcome to this new lesson of our second Quantum Optics course. In the previous lesson, you have learned what was the debate between Einstein and Bohr about the interpretation of quantum mechanics. The debate has been settled by a long series of experimental tests of Bell's inequalities, and the conclusion is clear: one must renounce Einstein's local, realist vision of the world. According to Einstein himself, we must therefore accept that the pair of entangled objects has weird properties that we can describe either as quantum non-locality or quantum holism. You are going to see today how these bizarre properties are at the root of several quantum technologies. Quantum non-locality is the fact that a measurement on one of the entangled object affects instantaneously the state of its partner, whatever is distance. This leads to applications in quantum communication of which you will see two. The first one is the Ekert protocol for a secure distribution of cryptographic keys to two distant partners. The other one is quantum teleportation, which permits quantum state transfer to a distant partner. These technologies are essential to the development of quantum networks, the so-called quantum Internet. Quantum holism is the fact that the quantum state of an entangled system can store much more information than would be expected by considering separately the individual components of the system. This opens fascinating possibilities of massively parallel calculations. That domain is evolving rapidly, and I will only superficially touch upon it. At the date of the recording of this lesson in June, 2019, it has evolved into two branches: quantum simulation on one hand, quantum computing on the other hand. Surprisingly, interesting connections have been recently established between the two branches and we have now programmable quantum simulators. This domain evolves very fast and what you will see in this lesson about quantum computing and quantum simulation is nothing more than a snapshot at the time of the recording. In section one, you will discover the Ekert protocol for Quantum Key Distribution for cryptography. It is a direct application of the experiments with polarization-entangled photons seen in the previous lesson, so you may want to have a look back at that lesson. In section two, I will tell you of the current limitation of that method, which can hardly extend beyond 100 kilometers unless one uses satellite distribution from space. I will also describe what would be quantum repeaters allowing one to extend the range, not only of the QKD protocol, but also, more generally, of quantum networks. A fascinating tool to achieve that goal is quantum teleportation, which will be presented in section four. But in order to understand quantum teleportation, you must first get familiar with Bell states and Bell measurements, an important tool in entanglement-based quantum technologies. Section four will present quantum teleportation, which is not what you have seen in Star Trek, but which is as fantastic for people who understand Quantum Physics as you. We will then turn toward the favorite subject of media: quantum computing. We will start in section five with quantum simulators, which already exist. In section six, I will tell you what would be a programmable universal quantum computer, which could solve some problems faster than the most powerful classical computer. This is the so-called quantum advantage. Universal quantum computers do not exist yet, and nobody knows whether they will ever exist. Fortunately, an intermediate version of programmable quantum computers has appeared in the recent years. It is based on quantum simulators which turn out to be richer than anticipated, and that line of research seems extremely promising to put the quantum advantage in action. In conclusion, after wrapping up as usual, I will tell you my vision of the future of quantum technologies. I have no doubt that future watchers of that sequence will laugh when they discover my naive anticipations. I think, however, that these predictions about future technologies, although usually wrong, are quite useful since they will allow future researchers to better realize where unexpected progress has happened.