Ground-state Cooling Of A Trapped Atom Using The Quantum Interference

The laser cooling of a trapped atom, a trapped ion or microscopic systems, has been a subject of intense research and is now a routine tool in many laboratories. Many interesting applications have been made possible by laser cooling, such as the direct observation of quantum jumps, high-precision spectroscopy and the preparation of atoms in the motional ground state. The ability to laser cooling of a atom to within the vicinity of the motional ground state is a key factor in the realization of efficient quantum computation. Various cooling schemes have been suggested and implemented, achieving lower and lower temperature and increased cooling rates. The schemes range from the simplest Doppler cooling to more sophisticated sideband cooling, resolved-sideband cooling, cooling schemes based on electromagnetically-induced transparency (EIT) and cavity-mediated laser cooling. Therefore, this thesis is devoted to the investigation of the schemes for the ground-state cooling of an atom in different systems.Firstly, we propose a cooling scheme for the V-type three-level atom tightly confined in a harmonic trap. Our approach is based on the two-level system with an auxiliary transition, where the carrier transition is eliminated by trapping the atom in the nondissipative lower dressed state. Meanwhile, we replace the restriction of the pair of the same Rabi frequency lasers in Stark-shift cooling scheme with a single weak laser, which is easier to realize. Two excited levels of the atom are coupled to the ground state by a quadrupole transition with a small dissipation rate and a dipole transition with a large dissipation rate, respectively. The quadrupole transition is strongly driven by a running-wave laser1, which acts as the cooling channel in the Lamb-Dicke regime. The dipole one is weakly driven by another running-wave laser2as the auxiliary transition. By using second-order perturbation theory in the Lamb-Dicke regime, we realize the ground-state cooling with a large rate through the appropriate choice of Rabi frequency for laser1and the detuning of the auxiliary transition.Secondly, we propose a ground-state cooling scheme for a trapped atom comprised of four levels in tripod configuration, where the atom is confined in a high-finesse optical cavity. D-ifferent from the cooling dynamics of the trapped atom in the intracavity EIT system, which demonstrates an efficient ground-state cooling with the elimination of carrier transition, the cooling scheme here merges the phenomenon of cavity-induced double EIT with the cavity quantum electrodynamics. Carrier transition can be eliminated due to the destructive quantum interference effect between excitation paths of one cavity-induced EIT when the involved one cavity photon and two laser photons fulfill the three-photon resonance condition. Meanwhile, the blue-sideband transition mediated by cavity field can destructively interfere with the appro- priate tuned additional transition between the third ground state and the excited state, leading to the elimination of heating process. As last, the trapped atom can be cooled to the motional ground state in the leading order of the Lamb-Dicke parameters. In addition, the cooling rate is of the same order of magnitude as that obtained in the cavity-induced single EIT scheme.Thirdly, we present a ground-state cooling scheme for a trapped A-configuration atom con-fined inside a highfinesse optical cavity, which can be cooled down by using a standing-wave cooling laser. We assume that the strength of the laser driving the cavity is sufficiently weak that the average photon number of the cavity mode is much smaller than unity. The carrier transition can be prohibited by placing the atom at the node of the cavity field, where the atom can not be irradiated by the field in the zeroth-order Lamb-Dicke parameters. In addition, the atom should be located at the antinode of the standing-wave cooling laser at the same time, where the atomic motion does not couple to the laser in the leading order of the Lamb-Dicke parameters. After a series of calculations, we get the explicit expressions for the cooling coefficients and zero heat-ing coefficient via tuning the frequency of the cooling laser. At last, the ground-state cooling for the trapped atom can be achieved. Moreover, we numerically demonstrate the superiority of using the standing-wave cooling laser as compared with the running-wave cooling laser, and the robustness of the scheme using the standing-wave laser. We also give the explicit expression for the final phonon number in higher order.In addition, We investigate a hybrid quantum system combining cavity quantum electrody-namics and optomechanics, where a photon mode is coupled to a four-level tripod atom and to a mechanical mode via radiation pressure. Our system is close to the regime of single-photon nonlinear optomechanical effects becoming significant. We focus on the strong coupling be-tween the atomic transitions and cavity field and neglect the external motion of the atom. The heating process can be dramatically suppressed via utilizing the completely destructive interfer-ence involving atom, photon and phonon, and it is only connected to the scattering of cavity damping path, which is also far-off resonance. The obtained result is analogous to that of the resolved sideband regime. Meanwhile, the cooling process assisted by the atomic transition can be notably enhanced. As a consequence, the ground-state cooling of movable mirror is achiev-able, and the enhanced cooling rate can make the cooled movable oscillator more robust against heating process and thermal noise.