  We propose a technique for polarizing and cooling finite many-body classical
systems using feedback control. The technique requires the system to have one
collective degree of freedom conserved by the internal dynamics. The
fluctuations of other degrees of freedom are then converted into the growth of
the conserved one. The proposal is validated using numerical simulations of
classical spin systems in a setting representative of Nuclear Magnetic
Resonance experiments. In particular, we were able to achieve 90 percent
polarization for a lattice of 1000 classical spins starting from an unpolarized
infinite temperature state.

Quantum Physics;Mesoscale and Nanoscale Physics;Other Condensed Matter;Statistical Mechanics