A Tractor Beam from Matter Waves

It was a surprise a few years ago that a steady light beam or sound wave hitting a small object could exert a pulling force on it. Now a team of theorists has analyzed such a “tractor beam” made from another kind of wave—the quantum-mechanical matter wave of a beam of particles such as electrons. Andrey Novitsky of the Technical University of Denmark and his colleagues found the conditions under which a matter wave would produce a pulling force.