Atomic Coherence Effects Of Rubidium And CPT Magnetometer

The interaction between coherent optical field and atoms led to a variety of atomic coherence effects, such as four-wave mixing (FWM), electromagnetically induced transparency (EIT) and coherent population trapping (CPT), electromagnetically induced absorption, entanglement state, which are always hot topics in quantum optics and has been applied in many practical applications. With the development of technologies, such as semiconductor laser, anti-relaxation coating, eliminating the spin-exchange relaxation, optical magnetometer also has received widespread attention, which based on atomic coherence effects. The sensitivity and spatial resolution of optical magnetometer could be comparable to the superconducting quantum interference magnetometer, but it does not need the low temperature environment. Our study focused on the atomic coherent effects in multi-level system of rubidium atom, we also have designed a magnetometer based on coherent population trapping practically, and found that it had good performance by analyzing the testing results.The effect of FWM is a nonlinear process that three coherent optical fields interact with atomic system and produce the fourth optical field, which is a most typical representative of multi-wave mixing effect. EIT is a phenomenon that using the atomic coherence to control the atomic properties of optical absorption and dispersion. These two phenomena can be generated in the same kind of atomic energy level structure, and we also can use the electromagnetically induced transparency to study the four-wave mixing effect.According to the equation of FWM, we studied the relationship of output signal of FWM effect, optical field detuning, optical field intensity and temperature of atomic system with Doppler Effect in 87Rb atom system. We found that the amplitude of four-wave mixing signal decreased with the increasing of temperature, and the signal decreased with the increasing of field intensity of control optical and pump light, and we also found that the output of four-wave mixing could be controlled by means of velocity of atoms? According to the equation of absorption and absorption coefficient, electromagnetic induction transparent and saturated absorption effect could be found in the output spectrum. We also studied the variation of output signals by changing optical field intensity and temperature of atomic system with Doppler Effect. According to the theory of three optical field interact with each other in three level system of A type, we built up the experiment system mainly consisted of two external cavity semiconductor laser and rubidium atomic vapor cell, it have verified electromagnetically induced transparency effect and saturated absorption effect according to the theory with the experimental system,.CPT is a phenomenon that atomic population of each energy level remains unchanged and the coherent optical fields do not vary with time evolution when coherent optical fields interact with atoms.In this paper, we mainly studied the CPT effect of A type energy structure and designed a magnetometer based on CPT and Zeeman effects. We also studied the basic principle of magnetometer to measure magnetic field using bichromatic linear optical field. According to the theory of sensitivity, we have proposed some methods to improve the sensitivity of magnetometer, and provided the reference value of atomic vapor cell.Based on the principle of measuring magnetic, we designed the scheme of the magnetometer and established the experimental system with circuits, optical configuration, laser and others. Based on the experimental system, line width of Vertical Cavity Surface Emitting Laser (VCSEL) is 0.13nm, the coefficient of wavelength to temperature is 0.0538 nm /?, and the coefficient of wavelength to current is 0.3245 nm/mA, frequency to voltage of voltage controlled oscillator 7166.7659 Hz / V, the line width of CPT is 0.64 Hz /V and characteristics of absorption spectrum of 87Rb. The resolution of magnetometer is less than 3nT, which agreed with the measurement result of commercial magnetometer GSM-19.Finally, we also studied the quadripartite entanglement of five levels atom and application prospect in magnetometer. We proposed a scheme to generate quadripartite entanglement by coherently preparing the five-level K-type atoms in a superposition initially. The conditions of initial atomic populations and atomic coherences to obtain the output genuine quadripartite entanglement have been analyzed numerically in detail. According to the structure feature of five-level atom, we analyzed the advantages and possibilities of using this kind of structure to design the optical magnetometer with better performance.