Strongly Coupled Cavity Quantum Electrodynamics And The Measurement Of Single Atom Trajectory

Cavity quantum electrodynamics (cavity QED) mainly focuses on the interaction between matter and electromagnetic field in a confined space. The basic model of cavity QED is the J-C model which treats the interaction between single atom and optical field inside a cavity. Since the early discovery by E. M. Purcell, who found that the spontaneous emission of an atom could be changed by the external environment in 1940s, cavity QED has made great development which benefited on the progress of the manipulation of atoms and molecules. As an important and subtle quantum system, cavity QED has greatly promoted the development of quantum physics and quantum optics. The cavity QED experiments have been a wonderful workhorse to explore the fundamentals of many quantum problems. When the interaction between single atom and cavity field reaches strong coupling regime, a single atom will have a big effect on the cavity transmission. Strongly coupled cavity QED has improved the sensitivity of single atom detection. Besides, it has been used in diverse areas such as generation of various quantum sources, for example, quantum entanglement and deterministic and controllable single-photon sources which are the foundation of quantum information process. Quantum internal states can be well controlled and detected by using cavity QED, for example, quantum entanglement between atom and photon or atom and atom by using the vacuum-stimulated Raman adiabatic passage (v-STIRAP). The condition of strong coupling is also necessary to achieve the reversible mapping of quantum states between atoms and photons, which provides the essential basis for quantum optical interconnects and is a fundamental primitive for quantum networks. Moreover, cavity QED system can be used for precision measurements and quantum metrology due to its ability to manipulate various quantum states with high probability and fidelity.In this thesis, focusing on the realization of strong coupling between single neutral Cesium atom and cavity and the measurement and control of single atom, we have finished some experimental works. The main works shown in the thesis are follows:1. The strong coupling between single neutral Cesium atom and cavity is obtained. We have built a cavity QED system,which includes high-finesse optical microcavity, vacuum and cold atoms system, frequency chain system, detection system and time sequence control system. The microcavity is placed in the ultra-high vacuum chamber. The length of cavity and the detunings are all controlled by the frequency chain system. Cold atoms trapped in the magneto-optical trap are right above the center of the microcavity. The detection system is used to detect the transmission of cavity. The parameters of our system is (g0,κ,γ)/2π=(23.9,2.6,2.6)MHz. The critical photon number and the critical atom number are m0=0.006 and N0=0.024, respectively.2. We demonstrate the trajectory measurement of the single neutral atoms deterministically using the high-finesse optical microcavity. Single atom strongly couples to a tilted high-order transverse vacuum TEM10 cavity mode. Thanks to the tilted TEM10 mode, which breaks the spatial symmetry and it thus helps us eliminate the degenerate trajectory of the single atom falling through the cavity and obtain a unique atom trajectory. The position of the atom is measured with a high precision of 0.1μm in the off-axis direction 5.6μm in vertical direction in a time interval of 10μs. The result is published in the form of rapid communication in Phys. Rev. A and is highlighted by Physics of APS.3. We demonstrate that light-induced atom desorption (LIAD) can be used for flexibly controlling the loading of magneto-optical traps (MOT) of Cesium atoms. A theoretical model based on an atom loading rate equation is built which can well explain the magneto-optical trap loading process with LIAD. The theoretical results are in good agreement with experiment.4. We experimentally demonstrate sensitive detection of individual Cesium atoms by using a high-finesse optical microcavity in a strong coupling regime. The atoms fall down freely in gravitation after shutting off the magneto-optical trap and pass through the cavity. The cavity transmission is strongly affected by the atoms in the cavity. The average duration of atom-cavity coupling is measured and is about 110μs. Strong coupling between single atom and cavity field has been achieved.5. We demonstrate an alternative method of measuring the temperature of cold atoms in magneto-optical traps using strong coupling cavity QED system. The microcavity is used as a point-like single-atom counter. The atoms fall down freely in gravitation after shutting off the magneto-optical trap and pass through the cavity. The temperature of the cold atoms in the MOT is determined by counting the exact arrival times of the single atoms. A theoretical model based on a ballistic expansion of a cloud of trapped atoms falling in the earth's gravitational field is used to fit the probability distribution of atom arrivals, and the temperature is obtained.6. We discuss the scheme to trap single atom in the cavity by FORT and the generation of deterministic single photon source based on our cavity QED system.