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Nature Physics 5, 682–686 (1 September 2009) | doi:10.1038/nphys1367

A phonon laser

K. Vahala , M. Herrmann , S. Kn|[uuml]|nz , V. Batteiger , G. Saathoff , T. W. H|[auml]|nsch & Th. Udem

Red-detuned laser pumping of an atomic resonance will cool the motion of an ion or atom. The complementary regime of blue-detuned pumping is investigated in this work using a single, trapped Mg+ ion interacting with two laser beams, tuned above and below resonance. Widely thought of as a regime of heating, theory and experiment instead show that stimulated emission of centre-of-mass phonons occurs, providing saturable amplification of the motion. A threshold for transition from thermal to coherent oscillating motion has been observed, thus establishing this system as a mechanical analogue to an optical laser—a phonon laser. Such a system has been sought in many different physical contexts.