Resolved Sideband Cooling In Cavity-Optomechanics With Si₃N₄ Membrane And Efficient Suppression Of Laser Noises

In the 17th century,radiation pressure forces of light were already postulated by Kepler,who noted that the dust tails of comets point away from the sun during a comet transit.The first unambiguous experimental demonstrations of the radiation pressure force predicted by Maxwell were performed using a light mill configuration.And the mechanical effects of light were theoretically derived when Maxwell proposed his famous equations.However,there were few application of this minute force for a long time.This changed until the invention of the laser,which enabled high intensity,coherent light sources.Radiation pressure of a highly focused beam became a tool to trap small particles in the 1970s.It was then used to laser cool the translational motion of individual atoms,and later led to the creation of Bose-Einstein condensate(BEC),which is a purely quantum state.In recent years,developments in micro-fabrication technologies and nanomechanical oscillator fabrication techniques eventually enabled radiation pressure to be applied to manipulate the motional mode of more macroscopic mechanical devices.This created a new frontier in physics,known as "cavity optomechanics".So far,devices have spanned from hundreds of nanometer to tens of centimeters,but they all intend to use radiation pressure to generate,detect,and utilize mechanical quantum states.In these applications,reaching the mechanical quantum ground state using laser cooling is an important goal.The device in our group consists of a high-Q silicon nitride membrane mechanical oscillator coupled to a high-finesse optical cavity.Our work presented in this thesis describes an effort to cool mechanical oscillator to ground state by using the resolved sideband cooling at a room temperature.I will first review some basic concepts in optomechanics,the physical properties of the membrane resonator,the optical cavity,and their mutual interaction.Then I will give the theory of resolved sideband cooling and the detection of mechanical motion.In the experiment,we design a high-Q,high-stress silicon nitride membrane and a high-finesse Fabry-Perot cavity and present the preliminary cooling down to 1/3131 at a room temperature.Moreover,in order to reduce the excess noises of light source which has the negative effects on cooling and is non-negligible in detection spectra,we propose and experimentally implemented an efficient filtering system for laser excess noise based on a cascaded imbalanced Mach-Zehnder interferometer.