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Topic Name: Schrödinger cat: The coherence also works with light!
Category: Quantum Computing
Research persons: Serge Haroche
Location: Paris, France
Details
A team of French researchers has just completed an experiment featuring the famous Schrödinger cat, not with the material, but with light. In agreement with the theory of decoherence, they were able to visualize the different stages of a quantum state in the classic.
A team of the Kastler Brossel Laboratory and the College de France just to talk with her experiences at the border of the classical world and the quantum world to probe the foundations of quantum theory. Among the names of the authors an article published by Nature, found that Serge Haroche, professor at College de France, famous for the decoherence experiments with Rydberg atoms. It was precisely to test the theory of decoherence, central to explain the paradox of Schrödinger cat, rather than in the case of matter, but of light.
Briefly recall what this paradox. In the quantum world, all aspects of the classical world are vague and in some ways potential. We can just talk about the probability of observing an object in a classic and it is forbidden to give an existence in the sense that we think, for example, that planets have a well-defined position and speed, and we are confident that our office computer still exists when we are not there to observe.
Schrödinger, like Einstein, could not bear this world view implied by the equations of quantum mechanics, including one bearing his name, Schrödinger equation. It sought to show that the quirks of quantum mechanics and its orthodox interpretation, that of Copenhagen, could not be confined by a cordon sanitaria around the world of atoms and should occur at our level.
Thus, if we saw a cat trapped in a box with a radioactive atom may disintegrate, it was necessary, according to quantum mechanics, consider the macroscopic object, ie the cat as one quantum object with the atom due to a phenomenon called quantum entanglement. However, according to the laws of quantum mechanics, the atom should be in a superposition of states. It could thus simultaneously disintegrate or not, only an observer looking at whether the break had occurred or not cause the passage of the state of the atom in one of these two alternatives.
Only then, if a Geiger counter was present in the box and can trigger the movement of a hammer to break a flask containing cyanide in case of disintegration of the atom, it led to a surprising conclusion: As one observer n 'Not opened the box to the cat out of the experience of thought proposed by Schrödinger, he was in a quantum superposition of states, both living and dead!
For Schrödinger, the fact that such a situation obviously not met in everyday life was proof that the orthodox interpretation of quantum theory was wrong. This does not convinced physicists like Heisenberg and Bohr and years later, an explanation was found: the theory of decoherence. In her view, the situation with a cat and a radioactive atom was a completely isolated view of mind and there is nowhere in the universe. The superposition of two states was in fact very fragile and slight disturbances from the external environment caused the destruction of the superposition in a time shorter than the one set to open the box by an observer.
This theory was tested a few years ago, notably by Serge Haroche and his colleagues, but with atoms, the theory she worked with entangled photons in a state of quantum superposition in a superconducting cavity walls? To find out, researchers have used the measure of what is called the Wigner function.
Introduced in 1930 by different physicists whose future Nobel Prize in Physics Hungarian Eugene Wigner, it is a powerful generalization of the wave function of Schrödinger, for instance, the probability of observing the position of an electron around an atom. There is a second wave function giving the probability of observing the electron with a given amount of movement and function of Wigner is a kind of fusion of these two descriptions into one. Applied to the case of entangled photons in the cavity before, this function which in this case depends on two parameters shows oscillations with positive and negative values that were represented in red and blue on the diagram below.
By passing the Rydberg atom in the cavity and measuring their status to the exit, it is possible to reconstruct the state of entangled photons and especially the Wigner function. In a few tens of milliseconds, while there is the oscillations of light disappear Wigner never let that positive values, ie precisely what is expected by decoherence theory of the disappearance of A state of entanglement with an overlay of death and a living for a Schrödinger cat.
As might be expected because of the dual wave-corpuscle, the theory of decoherence also works well in the case of light as in the field ...
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