Multi-level cold atoms in the EIT system to enhance the study of nonlinear effects

Title: Multi-level cold atoms in the EIT system to enhance the study of nonlinear effects Author: Han Yanxu Degree-granting units: Shanxi University Keywords: electromagnetically induced transparency;; MOT;; more dark state;; Tripod system;; cross-phase modulation;; optical thickness Abstract:
 Coherent light and the role of atomic physics in an important research content, the use of coherent light field and over the role of multi-level atomic
Process of quantum interference effects, Neodymium Magnets can produce a lot of interesting physical phenomena. Among them, the electromagnetically induced transparency (EIT) effect by people
General concern, due to reduced EIT medium with absorption and dispersion characteristics of rapid change, in the theoretical and experimental studies have been widely
.
 In the hot atomic vapor atomic physics experiments. Atomic thermal motion of atoms relative to the Doppler effect and
Each collision leading to decoherence effects to experiment brought many negative effects. With laser cooling and trapping neutral atoms and technological development
Cold atomic medium has become the http://www.everbeenmagnet.com/en/products/110-sintered-neodymium-magnets object of study as atomic physics and quantum optics focus of attention.
 This paper describes our experiments on
Establish a set of capture ~ (87) Rb magneto-optical trap cold atoms device to be captured by EIT effect of cold atoms in the observed multi-media
Dark-state phenomenon, the fine cold atomic energy levels in the preparation and magnetic measurements to study the interaction between dark state and trigger the light of the probe light
Enhanced nonlinear effects, and the transformation of the magneto-optical trap system to achieve a light pulse in the cold atomic medium in the storage and release. This
Completed work includes the following:
 1) a brief introduction to laser cooling and trapping neutral atoms in principle, a detailed
Units for cooling and trapping ~ (87) Rb magneto-optical atom trap device. Experimental method to measure the fluorescence collection had captured the number of cold atoms,
Cold atomic cloud size according to deduce the density of cold atomic cloud. The bottom of the cold atoms through the 4mm, 7mm, 10mm cylindrical three incident
Probe beam, the atomic process to obtain short-range free-fall time of flight (Time of Flight, TOF) absorption signal, through the numerical fitting
Get cold atom cloud temperature. The results showed that: the number of trapped cold atoms is about 10 ~ 9, the density is about 10 ~ (11) months / cm ~ 3, cold
But the temperature is about 200μK, the cold atom cloud EIT media can be used as well for our experimental study of atomic coherence.
 
2) observe cold atoms in multi-media phenomenon of the dark state, the magnetic fine level of preparation and distribution of atomic state population-based measurement. In many
Zeeman sub-level system of cold atoms, due to different transitions between Zeeman sub-levels of varying intensity and selection rule restrictions, only
Coupling probe light beam using a bunch of light can form two different EIT system and the width of an absorption system, and observed probe
Light of the multiple transparent windows. In the atomic system through the pump light to select the appropriate incident polarization direction and the direction of high-purity atoms can be
Degree of preparation in the atomic ground state Zeeman sub-levels on any. By the incident probe beam circularly polarized light, the distribution of populations of atoms into the
Line non-destructive measurement. This technology can be used in cold atoms in quantum information and quantum optics experiments being.
 
3) the interaction between dark state and the two beams between the nonlinear optical field cross-phase modulation. In the cold atomic medium, the use of state preparation technique
About 95% of the atoms prepared in the ground state Zeeman sub-level on one, select the appropriate polarization of the probe light, coupling light trigger
Light constitutes an ideal four-level Tripod structure. Coupling light in both resonance frequency of the trigger light conditions, between two dark states
Interaction, accompanied by enhanced non-linear effects, and the use of MZ interferometer measurement of the probe light of the phase change. Adjust the trigger light
The light intensity can be achieved on the probe nonlinear optical field cross-phase modulation, cross-Kerr nonlinearity coefficient to be a maximum of 7.2 × 10 ~
(-5) Cm ~ 2 / W, the nonlinear phase shift produced by 1 × 10 ~ (-2) rad, the results of quantum phase gate toward the goal of achieving a step forward.
 
4) high optical thickness of the magneto-optical trap system. As the original MOT trapping cold atomic medium unit optical thickness is low, can not meet the test
Further request, we will extend the cooling light beam diameter to 22mm, a tapered power amplifier (TPA) system to cool the light
Power amplification, to obtain high optical thickness of the cold atomic medium, and short-range by collecting fluorescence measurement of flight time to get cold the original
Sub-cloud size of 8 × 8 × 6mm ~ 3, the number of cold atoms is about 2.6 × 10 ~ (10), the temperature is about 250μK, mathematical fitting the probe light through the cold
Atomic cloud transmission signal to be trapped cold atomic cloud of optical thickness of 11. In order to further improve the optical thickness of the cold atomic medium,
The four magnetic field gradient by the 8G/cm gradually increased to 20G/cm, on the magneto-optical trap is compressed, the measured optical thickness of the cold atom cloud
16, the temperature is about 300μK.
 5) in high optical thickness of the cold atom cloud will produce a semiconductor laser into the laser probe
Pin light coupling light, and two round trips through the use of sound and light system will shift the frequency of the probe light shift 6.8GHz, observed that the probe light pulse
Cold atomic medium in the storage and release signals, and to study the release of the signal intensity with changes in the parameters of dependence.
 One record
New sex include:
 Ⅰ. The different Zeeman sub-atomic transition between the different intensity levels, in view of the cold atomic medium
Hot atoms in the police to observe more than the dark-state phenomenon, on this basis, by choosing different combinations of coupling light polarized pump light, the
Preparation of high-purity atoms in a magnetic fine any level, the measure proposed and demonstrated a sophisticated level atomic magnetic distribution of all populations
Optical methods.
 Ⅱ. The use of state preparation technique in the cold atomic medium, the preparation of more than 95% of the atoms in a particular
Zeeman sub-level, select the appropriate combination of the probe light polarization, coupling light and trigger the light to form an ideal four-level structure Tripod
. Coupling of the trigger light and light are resonant conditions, the study of the interaction between the dark state, the probe light for measuring light trigger non-linear cross-
Cross-phase modulation.
 Ⅲ. By expanding the cooling light spot diameter, a tapered power amplifier (TPA) system into the cooling power of light
Line amplification, to obtain a high optical depth (OD = 11) of the cold atomic medium, and measured the number of trapped cold atoms and optical thickness of the light with the cooling
The dependence of power changes. Four magnetic field gradient by the 8G/cm gradually increased to 20G/cm, further compressing the MOT, it can be light
Thickness further increased to 16 school. Degree Year: 2009