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'You're making me dizzy.'

What is the idea you have of an ensemble of many thousands of atoms? Well, it is hard to imagine, isn't it? Probably something you might think of is... chaos: atoms traveling in all directions in a crazy way, making collisions, spinning around... We like to put order into this chaos. In our experiment we first remove most of the kinetic energy laser-cooling the atoms. Then we isolate them by holding in an intense, focused beam. Finally we make them spinning all in the same direction, aligning their angular momentum that is the same to say we magnetize the sample.

Why we do this? Because after we make all this effort in minimizing the classical chaos, the interesting one manifests itself. It is the chaos resulting from the randomness of quantum mechanics, which in this way we can investigate.

Such inherent randomness affects for example the alignment of all the atoms. We can make them pointing all in the same direction, like one vector pointing from the center to the surface of a sphere. But, the Heisenberg uncertainty principle avoids this process to be perfect. The pointing of the vector is smeared into a disk of uncertainty.

What if we will be able to squeeze this disk into an ellipse? In fact this is allowed by the Heisenberg principle, which fix just the area not the shape of the uncertainty. Such spin squeezing corresponds to reduced fluctuation of one component of the angular momentum, and finds application for improved magnetic field sensitivity. Moreover, a reduced quantum noise of the sample means that the individual atoms have correlated their fluctuations in a way not explicable classically. Entanglement among the sample has been established.

We can perform spin squeezing on our ensemble of Rb atoms because of the high control we can achieve by interacting the atoms with polarized probing photons. Once we can order the chaos, what comes next? Can we really sense magnetic fields with improved precision? Can we manipulate and make use of the quantum correlation between atoms for computational purpose? There is a lot of science still to be studied.