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Results in Physics

Enhanced superluminal pulse propagation via chiral quantum dot system

Muhammad Idrees, Hui‐jun Li

Published May 15, 2024• 26 citations
Publisher

Abstract

The control and enhancement of superluminal pulse propagation via a chiral quantum-dots (QDs) system is presented in this article. The proposed system is a double chiral QDs four-level system, that gets excited by pump and probe fields, along with inter-dot tunneling strength. It is observed that the strength of inter-dot tunneling strongly influences the left-circular polarized (LCP) and right-circular polarized (RCP) superluminal pulse propagation. By appropriately modulating this strength, optimal coherence within the system can be achieved, thereby contributing to enhanced superluminal pulse propagation. We have examined the characteristics of RCP and LCP beams and observed the large negative group index and advance time. The observation of a large negative group index and advanced time shows strong evidence for enhanced superluminal pulse propagation in the proposed chiral QDs system. This study has important applications in the field of optical information processing, temporal cloaking, quantum communication, and improving computer chip speed.

DOI
10.1016/j.rinp.2024.107742

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The control and enhancement of superluminal pulse propagation via a chiral quantum-dots (QDs) system is presented in this article. The proposed system is a double chiral QDs four-level system, that gets excited by pump and probe fields, along with inter-dot tunneling strength. It is observed that the strength of inter-dot tunneling strongly influences the left-circular polarized (LCP) and right-circular polarized (RCP) superluminal pulse propagation. By appropriately modulating this strength, optimal coherence within the system can be achieved, thereby contributing to enhanced superluminal pulse propagation. We have examined the characteristics of RCP and LCP beams and observed the large negative group index and advance time. The observation of a large negative group index and advanced time shows strong evidence for enhanced superluminal pulse propagation in the proposed chiral QDs system. This study has important applications in the field of optical information processing, temporal cloaking, quantum communication, and improving computer chip speed.
The role of a chiral quantum-dot molecule (QDM) system in controlling and enhancing the Goos-H\"anchen (GH) shift is revealed here. The proposed setup is a four-level atomic system excited by incoherent pump and probe fields where the electron tunneling is prominent in affecting the GH shift upon the reflection and transmission of probe beams. The GH shifts in the chiral QDM system are calculated analytically by using stationary phase theory, whereas the dynamics of the quantum-dot system are derived by the density-matrix method. It is demonstrated that the GH shifts through transmission and reflection light beams are strongly influenced due to right-circularly polarized (RCP) and left-circularly polarized light. The GH shifts through RCP light are enhanced in the presence of chiral QDM systems, and these shifts could become either highly negative or highly positive, sensitively depending on the electron tunneling and chiral coefficients. This proposal can be viewed as a theoretical approach to the potential application of GH shifts in nano-optoelectronic sensors.
The structured vector fields of circularly polarized light , comprising both left and right (RCP and LCP) beams superposed in the atomic medium are investigated in this work. At resonance in the anomalous/normal dispersion area, both RCP and LCP beams with a non-negative and non-positive group index of ± 40 have been recorded. RCP and LCP beam group velocities are enhanced to ± 1 . 5 × 1 0 9 m / s at δ = 0 . 15 Γ , that is surpassing the speed of light in vacuum, denoted as ”c” leading to superluminal propagation. The RCP is superluminal and the LCP subluminal at the resonance point of the probe field. The group delay for The LCP beam is positive and the RCP beam is non-positive. The worth of the group delay for RCP and LCP beams varies to ± 4 n s . The superposing structured vectors field of superluminal and subluminal circularly polarized light beams on the right and left E R , L ( r , φ ) are strong variation function of detuning of probe field δ / Γ , Rabi frequency of control field Λ 3 / Γ and phase of collective driving fields φ . The results are useful for the modification of powerful computers.
Abstract We examine propagation of the linear polarized pulse through a medium containing four-level double V-type atoms. The medium is made chiral by the cross coupling of the applied electromagnetic fields. We show that such medium can be used as a polarization splitter of the probe pulse where the spatially refracted left and right circular polarized components propagate independently due to their distinct phase velocities. We find that dispersion characteristics of the chiral medium can be manipulated by the controlling parameters of the system. Consequently, both the left and right circular polarized components exhibit sub and superluminal propagation characteristics for suitable choices of the probe field detuning and external control fields. It is found that for both polarized components a switching from sub to superluminal behavior may be achieved by adjusting the probe field detuning. In addition, splitting of the left and right circular polarized components and hence peak value of the group time delay and advance may be tuned via the strengths of the control fields. Our results may find applications in spintronics, magnetic quantum optics, images coding and cloaking technology.
In this working, we introduce a Q-DD composed of two QDs. We find that the absorption and dispersion spectra of the light pulse can be changed via the effect of and inter-dot tunnel couplings and probe pumping field of QDs. Then, we employ the steady state and dynamical state in the four-level double QDs system. The slope of dispersion switches from positive to negative. Therefore, both superluminal and Subluminal light propagations can be achieved by simply applying a gate voltage to the double inter dot tunnel coupling. It is also demonstrated that by applying the indirect pump probe field to the probe transition the absorption-free superluminal light propagation is obtained. The results show that by proper tuning of the bias voltage. This structure also indicates that a wide range of linearity from negative to positive can be simply adjusted via a bias voltage, which would result in wide control of signal beam.
This study investigates the tunable propagation of optical pulses in a three-level system of coupled quantum dots. The system forms an effective closed configuration, supporting strong quantum coherence and controllable light–matter interactions. Using the density matrix formalism, we analyze the quantum dynamical response under the influence of both a weak probe and a strong control field, with inter-dot tunneling acting as a key tunable parameter. Our results reveal that both the tunneling strength (Te) and control field Rabi frequency (Ωc) play crucial roles in shaping the system’s optical properties. We observe the emergence of electromagnetically induced transparency-like windows, the splitting and shifting of dispersion peaks, and the formation of absorption doublets and transparency windows. The real and imaginary parts of the electric permittivity exhibit pronounced sensitivity to these external controls. Furthermore, the group index and group velocity are shown to be highly tunable, enabling transitions between slow-light and fast-light regimes. Detailed analysis of temporal pulse dynamics demonstrates the ability to achieve controllable delay and advancement of optical pulses, depending on the interaction between Te and Ωc. These findings highlight the potential of such quantum dot systems for dynamic photonic control, including applications in optical buffering, reconfigurable delay lines, coherent switching, and quantum information processing. The demonstrated tunability and coherence effects make this platform a promising candidate for next-generation optoelectronic and quantum photonic technologies.
We investigate the behavior of fast light pulse propagation in an N-type Doppler-broadened 4-level atomic system using double Raman gain processes. This system displays novel and interesting results of two controllable pairs of the double gain lines profile with a control field. The detailed physics of the processes are explored having multiple controllable anomalous regions in the medium. In this set up, the system exhibits significant enhancement in the probing Gaussian pulse through the medium as compared with Ref. [L. J. Wang, A. Kuzmich, and A. Dogariu, Nature \textbf{406}, 227(2000)]. The advance time of the retrieved Gaussian pulse is always greater than the advance time studied in the above said experiment. We analyzed that the pulse propagating through the medium with larger negative group index, 7.32×1087.32\times10^87.32×108, leaves the medium almost undistorted and sooner by time 76.12 ms76.12 \ ms76.12 ms than the pulse which leaves the medium of Wang \emph{et al.}. The Gaussian pulse always remains almost undistorted at output due to lossless characteristic of the medium. We also underlined the ways to suppress incoherences generated by the Doppler-broadening effect in the system. The limitations of the recently developed applications require to explore mechanisms for ultimate speed of a superluminal probe light pulse. In this connection, the proposed scheme may be helpful and can be easily adjusted with the current technology.