And then they need to interact with them, poke them individually with the right amount of force, make them see their neighbours, or make them feel isolated. One of the milestones in atomic control is the ability to shape a beam of light almost at will, which is what Zupancic and colleagues did. Aberrations influence the direction of light, the plane where it focusses, the curvature of the wave front and so on. Aberrations don't matter when you use a laser to play with your cat, but when you want to hit an atom, they really do!
In this work, the authors used a deformable array of microscopic mirrors (digital micromirror device, or DMD) to reflect a laser beam and make it in the shape they wanted. The mirrors can be programmed to move in the desired direction and correct for aberrations to one-fiftieth of the wavelength (that's about 10 nanometers), allowing the team to produce arbitrary potentials to push around the atoms in the array. And as they remind us in the conclusion, "Even better performance than demonstrated here can be achieved with DMD with more pixels, which are rapidly becoming available."
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