Laser cooling is a well-established technique in which the random motion or the temperature of neutral or charged atoms and molecules is reduced by dissipative optical radiation forces. Doppler cooling and sideband cooling methods are routinely used to cool these particles close to their vibrational ground state.
This is often a prerequisite for experiments in quantum optics and quantum information science.
Recent years have witnessed the emergence of long-wavelength radiation in the radio frequency (RF) regime as an alternative for ground state cooling. We investigate RF sideband cooling in which RF radiation is applied to the bare ionic states of one and two trapped ions exposed to a static magnetic field gradient. Our method showcases experimental simplicity avoiding the necessity of any additional dressing field. In addition, this cooling method is demonstrated at a low trap frequency that is often encountered also in neutral atom traps, thereby giving perspective to the application in ground state cooling of neutral atoms.
Furthermore, we demonstrate the first realization of sympathetic RF sideband cooling of a two ion crystal. A Doppler cooled ion (target ion) in the crystal is further cooled by applying RF sideband cooling on the second identical Doppler cooled ion (refrigerant ion). This complements the conventional sympathetic cooling using lasers.
- Radio frequency sideband cooling and sympathetic cooling of trapped ions in a static magnetic field gradient, T. Sriarunothai et al., Journal of Modern Optics DOI:10.1080/09500340.2017.1401137 (2017)