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Applied Physics

Influence of Vapor Pressure and Doppler Effect on the Optical Property of a Coherent Atomic Vapor

行 赵

Published Jan 1, 2013• 1 citation
Publisher

Abstract

研究了在不同温度下三能级相干原子气体的光学特性(介电系数和群速)色散行为。求解三能级原子系统完备密度矩阵方程,得到所有密度矩阵元的色散行为,然后考虑多普勒频移修正和原子气体饱和蒸汽压(饱和密度)随着温度的变化关系,进行数值求解,给出了探针光群速的色散行为及与原子蒸汽温度的函数依赖关系图示。本文所研究的不同温度下三能级相干原子气体的光学特性可以作为某些温控光子学器件(如光子开关、光逻辑门、光子晶体管)的基本物理原理。 The dependence of dispersion characteristics of electric permittivity and group velocity on the temperature in a three-level quantum coherent atomic vapor is considered based on the numerical solution of the density matrix equation of the three-level atomic system. The behavior of dispersion of all the density matrix elements has been obtained, and both the Doppler frequency shift and the saturation density that depend upon the temperature of the saturated atomic vapor have been taken into account. The presented optical response of the quantum coherent vapor can be utilized as a fundamental mechanism for some temperature-controlled photonic devices such as optical switches, photonic logic gates and optical transistors.

DOI
10.12677/app.2013.31005

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Influence of Vapor Pressure and Doppler Effect on the Optical Property of a Coherent Atomic Vapor

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研究了在不同温度下三能级相干原子气体的光学特性(介电系数和群速)色散行为。求解三能级原子系统完备密度矩阵方程,得到所有密度矩阵元的色散行为,然后考虑多普勒频移修正和原子气体饱和蒸汽压(饱和密度)随着温度的变化关系,进行数值求解,给出了探针光群速的色散行为及与原子蒸汽温度的函数依赖关系图示。本文所研究的不同温度下三能级相干原子气体的光学特性可以作为某些温控光子学器件(如光子开关、光逻辑门、光子晶体管)的基本物理原理。 The dependence of dispersion characteristics of electric permittivity and group velocity on the temperature in a three-level quantum coherent atomic vapor is considered based on the numerical solution of the density matrix equation of the three-level atomic system. The behavior of dispersion of all the density matrix elements has been obtained, and both the Doppler frequency shift and the saturation density that depend upon the temperature of the saturated atomic vapor have been taken into account. The presented optical response of the quantum coherent vapor can be utilized as a fundamental mechanism for some temperature-controlled photonic devices such as optical switches, photonic logic gates and optical transistors.
th , 2012; revised: Dec. 14 th , 2012; accepted: Dec. 23 rd , 2012 Abstract: The dependence of dispersion characteristics of electric permittivity and group velocity on the temperature in a three-level quantum coherent atomic vapor is considered based on the numerical solution of the density matrix equa- tion of the three-level atomic system. The behavior of dispersion of all the density matrix elements has been obtained, and both the Doppler frequency shift and the saturation density that depend upon the temperature of the saturated atomic vapor have been taken into account. The presented optical response of the quantum coherent vapor can be util- ized as a fundamental mechanism for some temperature-controlled photonic devices such as optical switches, photonic logic gates and optical transistors.
对三能级电磁感应透明原子系统的密度矩阵方程进行解算,获得该系统九个密度矩阵元的色散行为,同时研究探针光与控制光所对应的原子气体介电系数的色散曲线和一般相干操控特性。本文将控制光与探针光同等看待,即不同于以往着重于探针光特性、将控制光仅当作调控电磁感应透明介质光学特性的外部条件看待、从而没有研究控制光本身如何受探针光的影响。本文研究探针光与控制光之间的彼此影响(即彼此受对方操控的行为)。电磁感应透明介质内由光来控制光的量子相干行为可以作为新型光子学器件设计的基本原理。 The equation of motion of the density matrix of a three-level EIT (electromagnetically induced transparency) atomic system is solved and the behavior of dispersion of the nine density matrix elements is presented. The general optical response of the electric permittivity corresponding to both the probe and the control fields is addressed based on the numerical results of the equation of motion of the density matrix. The probe and the control fields are treated in the same way, in which the influence of the probe field on the control field (and vice versa) is considered. The optical be- havior of controlling light with light can be a fundamental mechanism for new photonic and quantum optical device design.
The author of this thesis concentrates his attention on quantum optical properties of some artificial electromagnetic media, such as quantum coherent atomic vapors (various multilevel electromagnetically induced transparency vapors) and negative refractive index materials, and suggests some possible ways to manipulate wave propagations inside the artificial electromagnetic materials based on quantum coherence and quantum vacuum effects. In Chapters 1 and 2, the author reviews the previous papers on quantum coherence as well as the relevant work such as electromagnetically induced transparency (EIT), atomic population trapping and their various applications. The basic concepts of quantum coherence (atomic phase coherence, quantum interferences within atomic energy levels) and quantum vacuum are introduced, and the theoretical formulations for treating wave propagations in quantum coherent media are presented. In Chapter 3, the author considers three topics on the manipulation of light propagations via quantum coherence and quantum interferences: i) the evolutional optical behaviors (turn-on dynamics) of a four-level N-configuration atomic system is studied and the tunable optical behavior that depends on the intensity ratio of the signal field to the control field is considered. Some typical photonic logic gates (e.g. NOT and NOR gates) are designed based on the tunable four-level optical responses of the N-configuration atomic system; ii) the destructive and constructive quantum interferences between two control transitions (driven by the control fields) in a tripod-type four-level system is suggested. The double-control quantum interferences can be utilized to realize some photonic devices such as the logic-gate devices, e.g., NOT, OR, NOR and EXNOR gates; iii) some new quantum coherent schemes (using EIT and dressed-state mixed-parity transitions) for realizing negative refractive indices are proposed. The most remarkable characteristic (and advantage) of the present scenarios is such that the isotropic left-handed media (with microscopic structure units at the atomic level) in the optical frequency band can be achieved. Quantum vacuum (the ground state of quantized fields) can exhibit many interesting effects. In Chapter 4, we investigate two quantum-vacuum effects in artificial materials: i) the anisotropic distribution of quantum-vacuum momentum density in a moving electromagnetic medium; ii) the angular momentum transfer between quantum vacuum and anisotropic medium. Such quantum-vacuum macroscopic mechanical effects could be detected by current technology, e.g., the so-called fiber optical sensor that can measure motion with nanoscale sensitivity. We expect that these vacuum effects could be utilized to develop sensitive sensor techniques or to design new quantum optical and photonic devices.In Chapter 5, the author suggests some interesting effects due to the combination of quantum coherence and quantum vacuum, i.e., the quantum coherent effects, in which the quantum-vacuum fluctuation field is involved. Two topics are addressed: i) spontaneous emission inhibition due to quantum interference in a three-level system; ii) quantum light-induced guiding potentials for coherent manipulation of atomic matter waves (containing multilevel atoms). These quantum guiding potentials could be utilized to cool and trap atoms, and may be used for the development of new techniques of atom fibers and atom chips, where the coherent manipulation of atomic matter waves is needed.In Chapter 6, we conclude this thesis with some remarks, briefly discuss new work that deserves further consideration in the future, and present a guide to the previously published papers by us.
Quantum interference and coherence lead to many interesting phenomenon and applications in quantum optics. In this dissertation, we study the quantum coherent properties in the following systems and aspects. We first investigate the optical bistability in a combined cavity-cold atoms system. In such a system the atom-photon interaction provides an optical lattice to the atoms and affects the mechanical motion of the atoms while atoms induce a position dependent phase shift on the cavity field. This highly nonlinearity induces optical bistability of intra-cavity photon number with respect to the pumping light added along the cavity axis. We show that the presence of this bistability can be controlled by a second pumping field added perpendicular to the cavity axis. It is also found that the critical input intensity of switching from one branch of bistability to the other depends on the the way of the field being added. This behavior is similar to the anomalous switching of the dispersive optical bistability of atomic media in the cavity. We also study the effect of counter-rotating terms in the control of spontaneous emission. We make use of a unitary transformation method and investigate the effect of dynamic energy shifts on the spontaneous emission modification via quantum interference in a four-level atomic system. We show that the counter-rotating terms, which are normally neglected in the usual investigation of atomic systems, do produce a significant influence on the evolution of the atomic amplitudes and the emission spectrum. This effect of counter-rotating terms can be observed in the time scale of the decay rate even when the dipole moments of the two upper levels are orthogonal to each other. The effect of counter-rotating terms on the spontaneous emission in a 3-D anisotropic photonic crystal is also discussed. It is shown that the behavior of the emission is similar to the case making rotating wave approximation, i.e., the localized and propagating fields are also separated by two characteristic atomic transition frequencies. However, the two characteristic frequencies are shifted due to the full Lamb shift which is obtained with counter-rotating terms being included in the Hamiltonian. We also utilize the unitary transformation method to show how the Lamb shift in a multi-level atom can be controlled by a driving field. Finally, we propose a subwavelength atom localization scheme for an atom located in a standing-wave field. The strategy is based on the observation that the photon statistics of resonance fluorescence depends on the position-dependent Rabi frequency.
Understanding the processes underlying the optical excitation of atomic vapor in the vicinity of solid surfaces is of interest both from physical and technical points of view. Selective reflection spectra of laser light from an interface of a transparent dielectric material and resonant vapor are known to be Doppler-free and to provide important spectroscopic information about the atom-wall interaction. On the other hand, atomic vapors have such a large and fast nonlinear response on or near resonances that they are capable of processing signals and images with milliwatt lasers at a time scale of submicroseconds. In the present paper we investigate linear and nonlinear optical properties of a thin film of atomic vapor confined between two solid surfaces. Assuming two-level atoms, we solve the Maxwell- Bloch equations for light reflection from resonant atoms. The interaction between the resonant atoms and the wall is accounted for through the boundary conditions for all elements of density matrix. The transient polarization is shown to make an important contribution not only to the field structure in the vicinity of the wall but also to the interference pattern of the reflected field. It is found that the spectrum of reflection depends remarkably on the film thickness. Strong enhancement of signal is also found from this study and possible devices for the detection are discussed.