Dynamics of phonon mode in superradiance regime of laser cooling of crystals

Eugene K. Bashkirov

The kinetics of the extended crystal doped by rare-earth ions in the regime of anti-Stokes laser cooling has been considered taking into account the collective radiation effects. The system of Markovian equations for impurities and pseudolocal phonons has been obtained. As would be expected, the collective radiation effects cause an acceleration in relaxation depletion of the phonon mode and, therefore, an increase in crystal cooling efficiency.

I. E. Mazets, Boris G. Matisov

Ivan Vybornyi, Artem Zhdanov, Matthias Bock +4 more

Low-entropy motional states of ion Coulomb crystals are an essential prerequisite for a plethora of applications and are typically prepared by laser cooling. As larger crystals are operated in the quantum regime, it remains unclear, and has recently become debated, whether increasing the ion number can be beneficial for cooling. Here, we investigate theoretically and experimentally many-ion sideband cooling and the role of collective effects in different spin-motion coupling regimes. For weak coupling, the many-body effects are insignificant. In the strong-coupling regime, however, the spin and motional subsystems undergo a coherent state swap, enabling cooling by a suitably timed laser pulse. Using planar Coulomb crystals with up to 91 ions, we demonstrate that the residual mean phonon occupation after one such pulse scales as $1/N^2$ with the number of ions. By iterating the pulses, we measure mean phonon occupations $<2\cdot10^{-4}$. For large crystals in the coherent regime, we further show that the spin-motion dynamics becomes largely independent of the initial phonon statistics. Through spin measurements, the state-swap mechanism can be utilized to probe the phonon distribution in the mode.

Evgenii Dmitrievich Trifonov

С. Н. Андрианов, В. В. Самарцев, Yu. E. Sheǐbut

Eugene K. Bashkirov, Башкиров Е. К

The process of laser cooling of an extended impurity crystal in a superradiance regime is explored with using the alternative scheme of a pumping of the impurity ions. Possibility of cooling of samples at the expense of collective radiation is shown.