A Crystal of Light and Atoms
Using an optical lattice, researchers can corral cold atoms into a crystalline array to simulate phenomena found in solids, such as magnetism and superconductivity. A theoretical proposal now shows how a crystalline phase could emerge without the artificial order imposed by a lattice. The scheme, which involves a uniform gas and lasers, mimics the spontaneous breaking of symmetry that occurs when a liquid becomes a solid, and it hosts wave-like lattice vibrations akin to phonons. The atom-light crystal may therefore offer a new way to simulate materials.
Helmut Ritsch and colleagues from the University of Innsbruck, Austria, considered a long, cigar-shaped Bose-Einstein condensate lying along the path of two counterpropagating laser beams. This setting allows for a dynamical atom-light interaction, in which the atoms move to the strongest regions in the optical field, and the refractive index is modified wherever the atoms bunch. The team found that, above a threshold laser density, this interaction causes the atoms to cluster into regularly spaced peaks. These peaks act as a diffraction grating for the beams, producing a periodic optical field, or a “light crystal.”
Such self-ordering has been predicted when the atoms and light are bounded within a cavity, but cavity walls cut off phonon-like excitations. Based on numerical simulations, Ritsch and colleagues suggest that their atom-light crystal would host a spectrum of phonon modes. These could be used to investigate phonon-mediated pairing interactions, like those that drive superconductivity in metals.
This research is published in Physical Review X.
Jessica Thomas is the Editor of Physics.
Spontaneous Crystallization of Light and Ultracold Atoms
S. Ostermann, F. Piazza, and H. Ritsch
Published May 24, 2016