Recently, much effort has been devoted to developing techniques that bridge the gap between laser cooling of atomic species and optical trapping of colloidal materials in order to study quantum phenomena at mesoscopic length scales. The aim is to explore and exploit quantum effects, e.g., entanglement, quantum superposition of motional states and long quantum coherence, in systems larger than atomic species. Experimentally, the first step towards this goal is the trapping and laser cooling of nanoparticles in vacuum, extending the methodologies used for neutral atoms and ions, which we discussed in Chapter 24. This trend fits naturally within the miniaturisation of optomechanics, i.e., the study and control of mechanical motion induced by optical forces. In particular, in optomechanical systems, thermal fluctuations of a mechanical oscillator can be reduced by the interaction with an optical field and, thus, the system can be effectively cooled by a controlled back-action of the light, as shown in Fig. 25.1. In this Chapter, we will explore these novel experimental schemes and how they open new perspectives towards the cooling of colloidal particles to their quantum motional ground state in vacuum.
25.1 Cavity optomechanics: The classical picture
25.2 Cavity optomechanics: The quantum picture
25.3 Laser cooling of levitated particles
25.4 Feedback cooling schemes
25.5 Below the Doppler limit