Control And Measurement Of High-Finesse Optical Microcavity And Cold Atoms

The cavity quantum electrodynamics (Cavity QED) mainly focuses on the interaction between single atoms and quantized electromagnetic field in a confined space. It has been provided a platform to test the principles of quantum electrodynamics and help people to get a deep insight into the fundamentals of atom-photon interaction. As one of the main methods for quantum information process (QIP) the cavity QED system has been a hot research field recently to demonstrate quantum computation based on the manipulation of individual atoms inside a cavity. In the strong-coupling-regime cavity QED, the atom-photon interaction (the Rabi frequency) is much larger than atom's spontaneous decay and cavity field decay, which means that the coherence effect of atom-photon system is overwhelming the decoherence of the system. In this case the evolvement of the atom-photon-cavity system can be seen as a coherent system and it makes the cavity QED system one of the prospects studying quantum entanglements, quantum decoherence process and quantum information science. The research of cavity QED, in the meantime, boosts the research of atom manipulation, single quanta detection etc.On one hand, the technique of laser cooling and trapping for neutral atoms comprehensively enhanced the ability of manipulating large number atoms, even single atom, in the free space. In the cavity QED experiment, however, a single atom needs to be captured inside a tiny space formed by a microcavity and this is still the main challenge. We retrospect in this dissertation some methods of getting single atoms trapped in optical domain cavity QED experiment, including optical lattices and tiny single optical trap with which single atom can be trapped by the blockade effect. We propose a new method, combined the single atom optical trap and microcavity, to capture deterministic single atoms inside microcavity. At present time, based on the free-falling configuration, we have designed and built our double MOT system and realized atom transportation from up-MOT to down-MOT and demonstrated the atom falling to the cavity.On the other hand, the cavity used in the optical domain cavity QED experiments usually has a length of tens micrometers and the cavity finesse is very high (usually from 10⁴ to 10⁶). High quality cavity implies long pthoton life time inside the cavity, which dramatically decreases the dissipation of the intracacity fields. And the short cavity means small cavity volume with high amplitude of a single-photon field, consequently, strong atom-photon interaction (Rabi frequency). All these efforts can bring the whole photon-atom system to the strong coupling regime. Clearly the microcavity plays a critical role in the whole experiment, including the cavity building, the parameter measurement and the cavity control. As one of the main part of this dissertation, we will introduce in detail our microcavity building procedure, parameters measuring methods, microcavity locking and control schemes. And eventually by chopping the cavity locking beam we observed the atom transits based on the microcavity and atom control.Moreover, cavity QED is an open quantum system and the intracavity atom-photon dynamic process can be known only by the leakage of the field through the cavity mirrors. By measuring the output field one can not only know what happened inside the cavity, but also prepare certain quantum states and control the atoms by quantum feedback. However, in the strong coupling regime the intracavity mean-photon-number is so small that the leakage power is usually at the level of pW. So a very sensitive detection system on single quanta level is needed and it is another important issue for the cavity QED experiment. We have theoretically analyzed and experimentally investigated the ultra-sensitive detection based on the balanced heterodyne detection as well as the single photon counting detection.The main works of this dissertation are as follows:1. We have built a microcavity by means of two super-mirrors with 100 mm of radius and measured the effective and physical lengths as L_eff= 44.627±0.004μm and L = 43.900±0.005μm , respectively. We also measured cavity linewidth asΔv = 47.8±1.5MHz , the corresponding maximum atom-cavity coupling factor and the cavity field decay rate are 2π×39.2MHz and 2π×23.9MHz, respectively. Since the decay rates of the Cesium atom D2 line is 2π×2.61MHz, the corresponding critical photon number and critical atom number are m₀=0.0022 and N₀=0.081 , respectively. This implies that our microcavity fulfill the requirements of strong coupling.2. We theoretically analyzed the reflectivities and transmissions of an arbitary F-P cavity with incident beams on both sides. And by measuring the TEM₀₀ mode matching efficiency we have accomplished the measurement experimentally with high precision and determined the transmission losses and other unwanted losses of an asymmetric microcavity. The measured results for mirror 1 and mirror 2 are: T₁ = 5.0(9) ppm , T₂ = 4.5(8)ppm, l₁ = 33.2(7)ppm,l₂ = 45.4(6)ppm, respectively.3. We built a balanced heterodyne detection system with two home-made RF detectors. The minimum detected power can be achieved as 3.7 fW, which corresponds to a mean intracavity photon number of 0.001 for our microcavity.4. We established a detection model based on the HBT scheme and modern single photon count module (SPCM) which is not photon number resolvable. The real experimental situations have been taken into account, including total detection efficiency, background noise and the property of SPCM. The detected second order degree of coherence, g⁽²⁾, has been comprehensively analyzed. We also finished the experiment measurement of g⁽²⁾ with coherent light and thermal light and confirmed our theoretical analyses. 5. We analyzed the stability of the microcavity length and the requirement of feedback loop for the cavity locking. By using the Pound-Drever-Hall method the microcavity has been controlled with length stability of 2 pm.6. Atom transits were observed with heterodyne detection when carefully controlling the atom falling and the microcavity with a chopped auxiliary locking beam.