Entropy Exchange and Thermodynamic Properties of the Single Ion Cooling Process.

A complete quantum cooling cycle may be a useful platform for studying quantum thermodynamics just as the quantum heat engine does. Entropy change is an important feature which can help us to investigate the thermodynamic properties of the single ion cooling process. Here, we analyze the entropy change of the ion and laser field in the single ion cooling cycle by generalizing the idea in Reference (Phys. Rev. Lett. 2015, 114, 043002) to a single ion system. Thermodynamic properties of the single ion cooling process are discussed and it is shown that the Second and Third Laws of Thermodynamics are still strictly held in the quantum cooling process. Our results suggest that quantum cooling cycles are also candidates for the investigation on quantum thermodynamics besides quantum heat engines.

Ground state cooling of an optomechanical resonator assisted by a Λ-type atom.

We propose a ground state cooling scheme for an optomechanical resonator based on the system of one Λ-type three-level atom trapped in an optomechanical cavity. This cooling scheme works in a single-photon coupling, and strong atom-cavity coupling regimes. By investigating the cooling dynamics, we find that there is an EIT-like quantum coherent effect in this system which can suppress the undesired transitions for heating. Moreover, our study shows that the final average phonon number of the optomechanical resonator can be smaller than the one based on the sideband cooling. Furthermore, the ground state cooling of the resonator can still be achieved after thermal fluctuations included. In addition, in comparison with previous cooling methods, there are fewer limitations on the decay rates of both the cavity and the atom in this scheme. As a result, this scheme is very suitable to realize the ground cooling of an optomechanical resonator in the experiment.