Cooling Mechanical Oscillator In Quantum Hybrid System

In physics,a quantum is the minimum unit of any physical entity involved in an interaction.The fundamental notion that a physical property may be "quantized" is referred to as "the hypothesis of quantization".This means that the magnitude of the physical property can take on only discrete values consisting of integer multiples of one quantum.In micro regime,a photon is a single quantum of light(or of any other form of electromagnetic radiation)and can be referred to as a "light quantum".Similarly,the energy of an electron bound within an atom is also quantized,and thus can only exist in certain discrete values.Atoms and matter in general are stable because electrons can only exist at discrete energy levels in an atom.Quantization is one of the foundations of the much broader physics of quantum mechanics.Quantization of the energy and its influence on how energy and matter interact(quantum electrodynamics)is part of the fundamental framework for understanding and describing nature.In macro regime,quantum refers to the macroscopic objects whose quantum phe-nomenon do not been covered by thermal noise and have a rather long coherent time.This objects usually refers to the mechanical system,mechanical oscillator,especially.Mechanical oscillator is regarded as the ideal candidate for exploring quantum behav-iors in macro regime.The first thing we need to do is to cool the oscillator to reduce the thermal noise and other noises,which makes the quantum behaviors could be well detected,not been covered by other noises.This thesis is divided into four main parts:In Chap.1,we mainly introduce the concept of quantized mechanical oscillator and its quantum description.We also introduce the quantum hybrid system,and some basic knowledge of Bose-Einstein-Condensate cold atoms.In Chap.2,we mainly introduce four cooling methods for the mechanical os-cillators,including cooling mechanical oscillator with a diluting refrigerator,feedback cooling,sideband cooling and back-action cooling.Chap.3 is our work,we introduce the hyperfine structure of magnetic trapped 87 Rb atoms,and simplify some of the sub-levels structure to a two-level system.By make an analogy between the out-coupled atoms with the out-put atom laser,the master equation of atom laser could be used in this cooling method.With further calculation,we derived the analytical solution for this method.We also explore the final temperature of and the mean phonon number of the mechanical oscillator by some experimental parameters.Further,we also explore the range of the mechanical oscillator's initial temperature,which could be cooled down to the quantum ground state.Chap 4 is the conclusion of this thesis.We hope this cooling method could be realized one day with the rapid development of the atom chip,the micro-nano technology and the control of the coupling between the oscillator and the atoms.