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Bohr played a central role in the interpretation of quantum mechanics. He based many discussions of its strange consequences on thought experiments. He imagined moving slit interferometers, able to record which path information, he played with photon boxes, storing photons for such long times that they could be weighed. The technological progress provided by quantum physics itself now make it possible to realize some of these thought experiments. We describe in this paper a few experiments based on microwave Cavity Quantum Electrodynamics (CQED) techniques. We trap photons in boxes and weigh them with scales at the atomic level. We are able to count the number of photons in the box without absorbing them in an ideal Quantum Non Demolition measurement of the field intensity. We can record which-path information in an atomic interferometer and directly illustrate complementarity. We can also prepare mesoscopic quantum superpositions reminiscent of the famous Schrödinger cat. We can get insight into the decoherence of these states and into ways to protect them, for instance by quantum feedback strategies.

DOI: 10.1007/978-3-319-14316-3_5

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