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Manipulating Spin-Torque Dynamics in Atomic Media with Electromagnetic Waves Interference

Amir Hamza, Muhammad Tariq, Abuzar Khan, Bakht Amin Bacha, Saeedullah Jan

Published Sep 26, 2023• 0 citations
Publisher

Abstract

Abstract In this article, Spin density and Torque of two interfering waves are controlled and manipulated by applying two interacting control fields and a probe field using a four-level N-type atomic configuration of Rubidium-87 isotope. The spin density of light can be controlled coherently in the atomic medium by electromagnetically induced transparency (EIT). When the strong interacting control fields and the weak probe field are applied to the atomic medium, the Rubidium atoms become transparent to the probe field. It is due to the control fields that "dress" the atoms, creating a new energy state that the weak probe field can interact with. As a result, the weak probe field can pass through the Rubidium atomic medium without being absorbed. Substantial variations can be seen in the electric SAM and Torque of two interfering waves with variations in the angle $\beta$ between the two interfering waves, the Rabi frequencies of the control fields, the detuning of the probe field, and the phase difference $\delta \phi$ between waves. By introducing these changes of parameters in the atomic medium, the spin density of two interfering waves can be made to rotate in a specific direction or at a specific rate. The parameters of control fields and probe field detuning play an essential role in the modification of electric SAM and electric spin vector field distribution of the probe field. The modified work of this manuscript is useful for Quantum computing, Optical communication, Quantum information processing. Key Words: Dynamical properties of light, Electric spin density, Two-wave interference, coherent control, Four-level N-type atomic configuration

DOI
10.21203/rs.3.rs-3364515/v1

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Abstract In this article, Spin density and Torque of two interfering waves are controlled and manipulated by applying two interacting control fields in which one is the Kerr field with Rabi frequency Ω2 and a probe field using a four-level N-type atomic configuration of Rubidium-87 isotope. The spin density of light can be controlled coherently in the atomic medium by electromagnetically induced transparency (EIT). When the strong interacting control fields and the weak probe field are applied to the atomic medium, the Rubidium atoms become transparent to the probe field. It is due to the control fields that ”dress” the atoms, creating a new energy state that the weak probe field can interact with. As a result, the weak probe field can pass through the Rubidium atomic medium without being absorbed. Substantial variations can be seen in the electric SAM and Torque of two interfering waves with variations in the angle β between the two interfering waves, the Rabi frequencies of the control fields, the detuning of the probe field, and the phase difference δϕ between waves. By introducing these changes of parameters in the atomic medium, the spin density of two interfering waves can be made to rotate in a specific direction or at a specific rate. The parameters of control fields and probe field detuning play an essential role in the modification of electric SAM and electric spin vector field distribution of the probe field. The modified work of this manuscript is useful for Quantum computing, Optical communication, Quantum information processing.

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Physical Review A•May 3, 2006•66 citations
Abstract In this article, Spin density and Torque of two interfering waves are controlled and manipulated by applying two interacting control fields and a probe field using a four-level N-type atomic configuration of Rubidium-87 isotope. The spin density of light can be controlled coherently in the atomic medium by electromagnetically induced transparency (EIT). When the strong interacting control fields and the weak probe field are applied to the atomic medium, the Rubidium atoms become transparent to the probe field. It is due to the control fields that "dress" the atoms, creating a new energy state that the weak probe field can interact with. As a result, the weak probe field can pass through the Rubidium atomic medium without being absorbed. Substantial variations can be seen in the electric SAM and Torque of two interfering waves with variations in the angle β\betaβ between the two interfering waves, the Rabi frequencies of the control fields, the detuning of the probe field, and the phase difference δϕ\delta \phiδϕ between waves. By introducing these changes of parameters in the atomic medium, the spin density of two interfering waves can be made to rotate in a specific direction or at a specific rate. The parameters of control fields and probe field detuning play an essential role in the modification of electric SAM and electric spin vector field distribution of the probe field. The modified work of this manuscript is useful for Quantum computing, Optical communication, Quantum information processing. Key Words: Dynamical properties of light, Electric spin density, Two-wave interference, coherent control, Four-level N-type atomic configuration
Abstract In this article, Spin density and Torque of two interfering waves are controlled and manipulated by applying two interacting control fields in which one is the Kerr field with Rabi frequency Ω2 and a probe field using a four-level N-type atomic configuration of Rubidium-87 isotope. The spin density of light can be controlled coherently in the atomic medium by electromagnetically induced transparency (EIT). When the strong interacting control fields and the weak probe field are applied to the atomic medium, the Rubidium atoms become transparent to the probe field. It is due to the control fields that ”dress” the atoms, creating a new energy state that the weak probe field can interact with. As a result, the weak probe field can pass through the Rubidium atomic medium without being absorbed. Substantial variations can be seen in the electric SAM and Torque of two interfering waves with variations in the angle β between the two interfering waves, the Rabi frequencies of the control fields, the detuning of the probe field, and the phase difference δϕ between waves. By introducing these changes of parameters in the atomic medium, the spin density of two interfering waves can be made to rotate in a specific direction or at a specific rate. The parameters of control fields and probe field detuning play an essential role in the modification of electric SAM and electric spin vector field distribution of the probe field. The modified work of this manuscript is useful for Quantum computing, Optical communication, Quantum information processing.
In the last few decades, coherent light-atom interactions have opened unprecedented possibilities for the coherent control of atomic and optical quantum systems, paved the way for the practical realization of quantum information technologies, and allowed for the creation of novel quantum-enhanced sensors. This dissertation investigates the interaction of multiple near-resonant optical fields with hot rubidium atoms under the conditions of electromagnetically induced transparency. The main goal of the presented research is to address some fundamental challenges in using such systems for practical applications. The EIT effect relies on the strong coupling of an optical probe field and a collective long-lived ensemble of atomic spins by the means of a strong classical optical control field in a Lambda configuration. While optically-thick atomic vapor is necessary to achieve such a strong coupling regime, the increasing optical depth of the atomic ensemble also leads to the effective enhancement of other nonlinear light-atom interactions, such as the four-wave mixing effect. Here we discuss the possibility to control four-wave mixing in a three-level system without deteriorating the coherent properties of EIT by introducing an additional absorber resonant exclusively with the Stokes field. The exclusive detection of a weak probe field in the presence of a strong control field is a challenging experimental task, especially at the few-photon level. Many experiments employ polarization and/or frequency filtering to compete the task. We present an alternative filtering technique based on optical vortices for cases when the traditional methods are not sufficient or restrict the experimental arrangements. Finally, we demonstrate the possibility to manipulate the group velocity of a pulsed squeezed vacuum field by using the optical dispersion modification via Zeeman spin coherence in rubidium atoms. By changing the interaction condition, we demonstrate the switch between the ``slow'' and (for the first time) ``fast'' light regime. We also show that increased optical depth simultaneously leads to the enhancement of pulse advancement and the deterioration of squeezing fidelity in the output pulses.
Atomic coherence and interference manifested by electromagentically induced transparency (EIT) and coherent population trapping (CPT) plays an important role in the current studies of atom-photon interactions and has found numerous applications in optical physics. EIT is created in a three-level atomic system by a coupling field and results in destructive interference between two excitation paths of a weak probe laser interacting with the atomic medium. This leads to suppressed linear absorption and rapidly varying atomic dispersion for the probe laser near the atomic resonance, which provides the platform for a variety of applications such as nonlinear optics at low light levels, slow light manipulation, and quantum state engineering for photons and atoms. Here we extend the simple three-level EIT system to more complicated and versatile configurations in a multi-level atomic system coupled by multiple laser fields. We show that with multiple excitation paths provided by different laser fields, phase-dependent quantum interference is induced: either constructive or destructive interference can be realized by varying the relative phases among the laser fields. Two specific examples are discussed. One is a three-level system coupled by bichromatic coupling and probe fields, in which the phase dependent interference between the resonant two-photon Raman transitions can be initiated and controlled. Another is a four-level system coupled by two coupling fields and two probe fields, in which a double-EIT configuration is created by the phase-dependent interference between three-photon and one-photon excitation processes. We analyze the coherently coupled multi-level atomic system and discuss the control parameters for the onset of constructive or destructive quantum interference. We describe two experiments performed with cold Rb atoms that can be approximately treated as the coherently coupled three-level and four-level atomic systems respectively. The experimental results show the phase-dependent quantum coherence and interference in the multi-level Rb atomic system, and agree with the theoretical calculations based on the coherently coupled three-level or four-level model system.
We investigate the generation of optical torque in coherently prepared multi-level atomic media driven by a vector vortex beam composed of two counter-rotating components carrying opposite orbital angular momenta, +lℏ+l\hbar+lℏ and −lℏ-l\hbar−lℏ. We consider a three-level ΛΛΛ configuration and a four-level tripod configuration. Using a perturbative steady-state solution of the optical Bloch equations, we obtain analytical expressions for both linear and nonlinear contributions to the optical torque. The results show that the torque is strongly controlled by atomic coherence, including the initial population imbalance and the relative phase between the vortex components. Nonvanishing torque can arise even when the two components have equal amplitudes, due to coherence-induced asymmetry in the atomic response. In the tripod configuration, the presence of a strong control field leads to electromagnetically induced transparency, which suppresses the torque near resonance and shifts the dominant response to finite detunings. These results establish a route for controlling light-induced rotational dynamics in atomic media using vector vortex fields, with potential applications in coherent optical manipulation and angular-momentum-based control in quantum systems.
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.
We propose and experimentally demonstrate a mechanism to achieve coherent control of the polarization rotation of an optical field in a multilevel electromagnetically induced transparency (EIT) system in rubidium atoms. By choosing a properly polarized coupling field and transition energy levels, the symmetry of the atomic medium to the propagation of two orthogonal polarization components of a weak linearly polarized probe field can be broken, which leads to a coherently controlled rotation of the probe field polarization. This mechanism of coherently controlled optical polarization rotation makes use of asymmetry in EIT subsystems for the two circular polarization components of the probe beam with a contribution from different transition strengths (due to different Clebsh-Gordan coefficients) in this multilevel atomic system.