Atomic coherence

About: Atomic coherence is a research topic. Over the lifetime, 877 publications have been published within this topic receiving 29395 citations.

Theory for Raman superradiance in atomic gases

Abstract: A mean field theory for Raman superradiance (SR) with recoil is presented, where the typical SR signatures are recovered, such as quadratic dependence of the intensity on the number of atoms and inverse proportionality of the time scale to the number of atoms. A comparison with recent experiments and theories on Rayleigh SR and collective atomic recoil lasing (CARL) are included. The role of recoil is shown to be in the decay of atomic coherence and breaking of the symmetry of the SR end-fire modes.

Entropy Evolution of the Bimodal Field Interacting with an Effective Two-level Atom Via the Raman Transition

Abstract: The properties of entropy evolution of the bimodal field interacting with an effective two-level atom via the Raman transition are studied. The influences of the initial average photon number and of the atomic coherence on the evolution of the bimodal field entropy are examined. It is shown that the bimodal field is in a pure state only under certain conditions in the early stages of time evolution and later tends to a statistical mixture state with maximum entropy values; the bimodal field remains strongly entangled with the atom.

Atomic coherence changes caused by optical pumping applied to electromagnetically induced absorption

Abstract: We have investigated atomic coherence changes caused by optical pumping applied to electromagnetically induced absorption (EIA) occurring at the open system, which consists of the transition between the Fg = 2 ground state and the Fe = 3 excited state in the 85Rb D1-line. For optical pumping, another laser resonantly tuned to the transition between the Fg = 3 ground state and the Fe = 2 excited state was used. We found that the atomic coherence for EIA can be changed not by increasing the pumping rate but by pumping differently populations into the Zeeman sublevels in the Fg = 2 ground state, which is realized by changing the polarization of the pumping laser. The experimental results were able to be analysed by density matrix equations in the simple model system.

Thermometry and coherence properties of a ultracold quantum gas of metastable helium

Abstract: In 2001 metastable Helium (He*) attained Bose-Einstein condensation (BEC). The metastable state has a lifetime of 9000 sec and an internal energy of 20 eV. This energy can be used to detect individual atoms using a micro-channel plate. The extremely good time response and high gain of this detector makes it possible to carry out a density correlation measurement (HBT) with massive particles similar to the pioneering experiment of R. Hanbury Brown and R. Twiss in optics. In addition, inelastic collisions between He* atoms produce a small but detectable flux of ions proportional to the cloud's density. This allows one to follow the evolution of the cloud's density toward BEC, passing through the phase transition, in real time and in a non invasive way. In this dissertation we report on three different experiments: i) the determination of the two- and three-body ionizing rate constants of He*; ii) the determination of a, the He* scattering length; iii) the measure of the intensity correlation function of a falling He* cloud. It has been shown lately that our measure of a was affected by a large systematic error and we propose a possible explanation. We describe methods to determine the temperature and fugacity of a thermal cloud. Finally a major portion of the thesis is devoted to the derivation of an analytical expression for the intensity correlation function of the atomic flux. This theoretical analysis has derived typical values for the transverse and longitudinal atomic coherence length that confirmed the possibility of performing a HBT experiment with our apparatus.