Sorting individual atoms in 3D: an omniscient Maxwell's demon

Combining site-resolved imaging, site-selective state flips and state-dependent motions, we have sorted atoms in randomly half filled 5x5x5 3D optical lattices into 96{\%} filled 5x5x2 or 4x4x3 sub-lattices. The sub-lattice ends up perfectly filled \textasciitilde 30{\%} of the time. Our experiment realizes the full essence of a Maxwell demon [Phys. Rev. A \textbf{70}, 040302(R) (2004)]. The sorting reduces the apparent configurational entropy by a factor of 8 and the total entropy by a factor of 2.4. The resulting manifestly low entropy state would be comfortably below the quantum degeneracy threshold if the lattice were adiabatically shut off and the atoms left in a 3D box trap [Phys. Rev. Lett. \textbf{89}, 090404 (2002)]. We will use the result of our Maxwell demon as the initial state of a neutral atom quantum computer.