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Journal of Military Science and Technology

Controllable light group velocity in a degenerate two-level medium under the assistance of an external magnetic field

Dong Hoang Minh, Thai Doan Thanh, Nguyen Thi Thu Hien, Trang Huynh Dang Khoa, Le Van Doai, Nguyen Manh Thang

Published Feb 25, 2024• 0 citations
Publisher

Abstract

In this work, we proposed a simple model for control of subluminal and superluminal light propagation via an external magnetic field in a lambda configuration degenerate two-level atomic medium. We show that the absorption-dispersion properties and group index under the influence of the strength of coupling laser and external magnetic fields are controlled. By changing the direction and magnitude of the magnetic field, the medium switches from transparency with normal dispersion to enhanced absorption with anomalous dispersion at the line center, corresponding with the transfer from slow light to fast light. This work may provide for the application realization of magneto-optic switches and storage devices in quantum information processing.

DOI
10.54939/1859-1043.j.mst.93.2024.106-113

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In this work, we proposed a simple model for control of subluminal and superluminal light propagation via an external magnetic field in a lambda configuration degenerate two-level atomic medium. We show that the absorption-dispersion properties and group index under the influence of the strength of coupling laser and external magnetic fields are controlled. By changing the direction and magnitude of the magnetic field, the medium switches from transparency with normal dispersion to enhanced absorption with anomalous dispersion at the line center, corresponding with the transfer from slow light to fast light. This work may provide for the application realization of magneto-optic switches and storage devices in quantum information processing.
Abstract We proposed a simple model for investigating subluminal and superluminal light propagation via an external magnetic field in an inhomogeneously broadened degenerate two-level atomic medium. We show that a magnetic field can be utilized as a knob to control the absorption/dispersion properties and group index of the medium. By changing the magnitude and reversing the direction of the magnetic field, the positive group index is converted to the negative group index at the center of the EIT window, corresponding with the propagation of a weak light pulse from subluminal to superluminal. Moreover, the influence of the Doppler broadening effect on the group index is also included, making the results approach to actual conditions. Therefore, the suggested model may be helpful for the application realization of optical storage in quantum computers and quantum information processing.
Abstract Magnetic field plays an important role in studying the transient response because the transition probabilities of degenerate energy levels depend on the external field. The application of an external magnetic field is of particular interest, as the magnetic field is readily available and more flexible to control than an additional laser field, which is an essential consideration in our paper. In this work, we propose a simple model for managing the transient absorption and dispersion properties in a degenerate two-level atomic medium under both transparency and absorption regimes in the presence of spontaneously generated coherence (SGC), an incoherent pumping field, and an external magnetic field. We show that a magnetic field can be utilized as a ‘knob’ to swap the transient absorption and dispersion properties of the system in both transparency and absorption regimes. The magnetic field not only aids in creating transparency and absorption regimes but is also helpful in controlling the system operating at different frequency regions for the probe field without changing the frequency of the coupling field; SGC is introduced to enhance the laser phase dependence of the atomic optical properties, while the incoherent pumping field plays a role in enhancing the effects of SGC and relative phase on the atomic optical properties. The influences of SGC, relative phase, and incoherent pumping rate on transient response are also considered to improve the stability of transient absorption and dispersion properties. Moreover, the essential time required for swapping between subluminal and superluminal light propagation is also provided. The proposed model shows that the system can be used as an ultrafast optical switch, which, in practice, may enable control over switching rates in quantum storage and information-processing devices.
Abstract The present study addresses light propagation in both the positive- and negative-group-index regimes in a degenerate atomic system with four energy levels. Both the static magnetic field and the Doppler shifts play essential roles. Operating in an electromagnetically induced transparency configuration, we demonstrate that probe absorption characteristics and the group velocity index can be manipulated by combined control of the static magnetic field and two coupling laser fields. By selectively engaging one or both coupling fields, the magnetic field serves as a switching mechanism, toggling the atomic medium's optical behavior between transparent and absorptive states. Consequently, both the magnitude and sign of the group index can be adjusted, transitioning from positive to negative values or the reverse, based on whether the magnetic field is applied or removed. Additionally, temperature significantly influences both the optical properties and group index characteristics of the atomic medium. Given that our proposed system operates at room temperature, it is well-suited to practical experimental conditions and offers potential for deployment in optical storage technologies and quantum information processing applications.
We theoretically investigate the optical response of a degenerate four-level Λ\LambdaΛ-type atomic system under the influence of an external magnetic field. The applied magnetic field lifts the degeneracy of the ground sublevels via the Zeeman effect, thereby altering the two-photon resonance conditions for electromagnetically induced transparency (EIT) formation and causing the atomic response to evolve from single-EIT to double-EIT, accompanied by shifts in the EIT positions. Such variations in the EIT positions result in corresponding changes in the dispersion and group index curves, allowing the selection of desired frequency regions for different response regimes. As a result, the system can switch between transparency and absorption, as well as between slow and fast light. These findings highlight the feasibility of controlling light propagation via magnetic field, with potential applications in optical switching and quantum information technologies.
Abstract Optical properties including absorption, dispersion, group index, Kerr nonlinearity, and optical bistability of a three-level V-type atomic medium have modified by varying an external magnetic field. By changing the magnitude or the sign of the external magnetic field, the transparency window with normal dispersion transfers to the enhanced absorption with anomalous dispersion at the line center, and hence the light propagation switches between subluminal and superluminal modes. The magnitude and the sign of the Kerr nonlinearity are controlled with the strength and the sign of the magnetic field. As a consequence, the behaviors of optical bistability are also made to appear or disappear when switching on/off the magnetic field. Moreover, the threshold intensity and width of optical bistability are also changed by the magnetic field and the coupling field. The results can be used to control the working characteristics of applied devices and study the related effects.
We have shown that quantum interference in a driven quasi-degenerate two-level atomic system can be controlled by an externally applied magnetic field. We demonstrate that the mechanism of optical control is based on quantum interference, which allows one to implement both electromagnetically induced transparency and electromagnetically induced absorption in one atomic system. Dispersion of such the medium allows one to control group velocity of propagation of light pulses be ultra-slow or superluminal via applied magnetic field.