Cecilia Cormick, Giovanna Morigi
Singly-charged ions in traps can form strings at low temperatures, where ordering is due to the interplay of the confining potential and the Coulomb repulsion. When an optical transition of the ions strongly couples to the mode of a high-finesse resonator, the mechanical force of light concurs in determining the crystal properties. Such force depends on the position of all ions coupling to the field, and is a manifestation of a photon-mediated interaction. While this interaction is usually small compared to the Coulomb repulsion, it can become significant close to a structural instability. We analyse the mechanical properties of an ion chain close to the linear-zigzag transition, and show that the instability can be driven by the intensity of the laser pumping the resonator. At large cooperativity, in particular, parameter regimes are found for which both linear and zigzag arrays are stable in finite chains, in contrast to free space where the structural transition is continuous. For these regimes photonic and vibrational excitations are strongly coupled. This effect is visible in the spectrum of light at the cavity output. When the crystal vibrations are cooled by the cavity field, Fano-like resonances are observed, signalling quantum correlations between photons and crystal.
View original:
http://arxiv.org/abs/1203.0470
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