Quantum Coherent Control Of Spontaneous Emission And Ionization Rate

Spontaneous emission is an important subject of physics for it is one of three basic processes of light interacting with matter. It induces some important phenomena such as quantum noises of photoelectric equipments, limited breadth of laser. Researchers have devoted themselves to cancel or restrain spontaneous emission by certain means. In recent years, quantum interference has been widely used to control the spontaneous emission and many physical effects caused by quantum interference such as Spontaneous Emission Restraint and Cancellation, Super-narrow Spectrum, Electro-magnetic Induced Transparency, and Lasing Without Inversion have been founded in theory and experiment. Early laser-based attempts at control relied either on frequency resolution of lasers to locate a frequency or on the high-power lasers to alter the dynamics. The common drawbacks of them are strong background and the use of high-power is limited in practice, so much attention has been turned to coherent phase control techniques.In this paper, we investigated the coherent control of spontaneous emission in three level system. In our system, the ground state is driven to the excited state with laser field that has different initial phase. The main conclusion through varying initial phase as follows:The distribution of the spectral line with three peaks is symmetric for energy splitting. When the initial phase difference is zero, the central peak is lower than the side peaks. With the increase of the initial phase difference, the distance of two sides peaks increases and the height of them decrease, but the height of the central spectral line increases. When the initial phase difference equals to Pi, the two sides peaks vanish and central spectral line becomes a sharp line, which realize the completely restraining effect of the side peaks.Considering dressed state | 1 > relates to bare state |1 > and |3 > , the population oscillate between the bare state |1 > and |3 > when system populates in | 1 >, so we can realize efficient population transfer by utilizing control the dressed state |1 >.Selectively ionizing atoms(or molecule) can be easily performed by means of a multistep resonance photoionization technique. Generally, one or two beams are employed to excite atoms from ground state into a bound state and another laser pumps atoms from the bound state into an ionization state. In this scheme, all the laser fields must be intense enough to ensure the high probability of ionization and must interact with atoms simultaneously. Because of the low efficiency of photo ionization lots of energy are wasted, it is important to improve the efficiency of it and lower the laser power. The population highly depends on the Rabi frequencies and the detunings. In general almost all the population are trapped in the ground state when the parameters are badly matched as if there is no fields. Although the line shape and the lifetime of the autoionization state may be manipulated, the high power laser field must be satisfied.In this paper, photoionization of three ladder level system is studied utilizing Runge-Kutta. It is shown that the population oscillate highly for the simultaneous exciting and intense laser field is needed in the traditional scheme. We can realize completely efficiency ionization probability under the condition of low Rabi frequencies by employing lower power and time-delayed laser pulse.The superposition is formed between the bound state and the autoionization state for the intense Rabi frequencies. The population of symmetric superposition is the same to that of asymmetric superposition, and the both are modulated by the delay tune.