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Shedding new light on Schrödinger’s cat.

Professor Serge Haroche, Ecole Normale Supérieure and Collège de France, Paris.

Abstract: In the early days of quantum physics, the founding fathers of the theory used to imagine “thought experiments” in which they assumed that they were manipulating and observing isolated atoms or photons evolving according to the strange and counterintuitive laws which they had just discovered. At that time, they believed that these experiments would remain forever virtual. Technological advances have recently changed this state of affairs and made possible the actual control and manipulation of isolated quantum particles, in ways which were previously thought impossible to achieve. At the fundamental level, the goal of these studies is to explore the transition between the microscopic world where quantum laws are dominant and our macroscopic environment which appears to be “classical”. More practically, physicists are hoping that these experiments will open the way to new technologies exploiting the strange logic of the quantum world to compute, communicate or measure physical quantities better than what was previously conceivable. In Ecole Normale Supérieure in Paris, we perform such experiments by juggling with atoms interacting with photons trapped between highly reflecting mirrors. We have realized the non-destructive counting of photons and the preparation of states of radiation analogous to the famous “Schrödinger cat” that the Austrian physicist had imagined to be suspended between life and death. We have also studied the decoherence of these states, i.e. the process by which they lose in a short time their strange “quantumness”. I will give a simple description of these experiments and try to make a few guesses about their possible applications.