Cooling crystals by disorder
Prof. Dr. Giovanna Morigi (Theoretische Physik, Universität des Saarlandes)

Trapped one-component plasmas at low temperatures organise in ordered structures which minimise the potential of the external trap and of the Coulomb repulsion. In presence of a pumped standing-wave resonator, to which the ions dipolar transitions strongly couple, the potential also comprises the optical lattice of the cavity, which mediates infinitely long-ranged interactions between the ions. We analyse the dynamics of the ions vibrations when they form a chain and the ordering imposed by the cavity potential competes with the Coulomb interaction. In this regime, depending on the parameters, the chain ground state can be in a sliding or in a pinned phase. Here, the defects (kinks) couple the chains normal modes with the cavity field fluctuations and the cavity field can act as a tunable reservoir which is controlled by the parameters of the external pump and may cool the chain modes. We show that, due to the cavity nonlinearity, changing the structural phase of the crystal can modify and/or enhance the effect of cavity cooling. Close to the Aubry transition, localised modes of the chain can be individually cooled to the zero-point motion and become strongly correlated with the cavity field fluctuations. Deep in the pinned phase, instead, the whole normal modes of the chain can be efficiently brought to the ground state and cavity field fluctuations are suppressed. We connect our predictions with the features of the spectra of the light at the cavity output, which allows one to non-destructively monitor the coupled dynamics.