Abstract The optical properties of a weak probe light by applying coupling fields in Landau-quantized graphene nanostructure is investigated. In this structure the electromagnetic field of terahertz-infrared radiations interfere with the electromagnetic field of the short-wavelength probe field and this effect changes the absorption and dispersion characteristics of the probe field. The linear dynamical properties of the graphene by means of perturbation theory and density matrix method are discussed. We show that the group velocity of a light pulse can be switched from superluminal to subluminal or vice versa by controlling the coupling field’s intensities and relative phase of the applied fields. Therefore, this model can be used as an all-optical switch which is suitable for next generation of future all optical quantum communicational system and networks.
Abstract The optical properties of a weak probe light by applying coupling fields in Landau-quantized graphene nanostructure is investigated. In this structure the electromagnetic field of terahertz-infrared radiations interfere with the electromagnetic field of the short-wavelength probe field and this effect changes the absorption and dispersion characteristics of the probe field. The linear dynamical properties of the graphene by means of perturbation theory and density matrix method are discussed. We show that the group velocity of a light pulse can be switched from superluminal to subluminal or vice versa by controlling the coupling field’s intensities and relative phase of the applied fields. Therefore, this model can be used as an all-optical switch which is suitable for next generation of future all optical quantum communicational system and networks.
Abstract In this paper, we investigated the behaviors of the absorptive-dispersive properties of weak probe light based on quantum coherence and interference in a Landau-quantized graphene nanostructure driven by coherent pumping fields. The linear dynamical properties of the grapheme are discussed with reference to the density matrix method and the perturbation theory. It is found that under certain conditions and by an appropriate selection of the parameters of the medium, the absorption, dispersion and group index of the weak probe light can be controlled. Moreover, the superluminal light propagation in the system is accompanied by amplification to make sure that the probe field is amplified as it passes through the system via adjusting the corresponding controllable parameters such as the intensity, the detuning and the relative phase of the applied fields. Moreover, it is observed that the probe amplification can be obtained in the presence or absence of population inversion by properly choosing the system’s parameters. We hope that these results may have useful application in future quantum communicational systems and networks.
In recent years, control of group velocity of light has attracted enormous interest. One of the main challenges is to realize an absorption-free fast or slow light propagation. Here, we study dispersion and absorption properties of a weak probe field in a Landau-quantized graphene and report a gain-assisted superluminal light propagation. Moreover, an attempt is made to develop an analytical expression and necessary parameters for switching the group velocity of the probe field from subluminal to superluminal. It’s worth mentioning that large dephasing rate in graphene offers feasibility of superluminal propagation of ultrashort light pulses. Additionally, dynamical behavior of dispersion and absorption of a weak probe field in a closed-type graphene system is investigated, and it is found that the absorption and dispersion can be dramatically affected by both the relative phase of applied fields and the Rabi frequencies in such a way that a large transient gain can be achieved and a transient absorption can be completely eliminated.
The dispersive-absorptive optical properties of a weak probe field are investigated based on quantum coherence and interference in a Landau-quantized graphene structure. It is found that an enhanced refractive index with vanishing absorption can be obtained in this structure through proper adjusting the controlling parameters of the system. The switching between superluminal and subluminal light propagation is also discussed. Our scheme can be employed in real experiments to develop new types of nanoelectronic devices for realizing all-optical switching process and can have practical application in dispersion compensation and solid-state quantum communication.
This article presents an exclusive study of the linear and higher-order susceptibilities, as well as the reduction in group index of a weak probe pulse in a three-level Landau-quantized graphene (LQG) system, under the influence of a strong control field, utilizing the phenomenon of electromagnetically induced transparency. The influence of the magnetic field on the higher-order nonlinearities (Kerr, quintic, and septic) leads to observable changes in amplitudes and shifts in probe frequencies. The LQG system exhibits giant values for these nonlinear susceptibilities with χ(3), χ(5), χ(7) reaching magnitudes approximately ∼10−18m3/V2, ∼10−30m5/V4, and ∼10−42m7/V6, respectively, in the mid-infrared range. The magnetic field also induces asymmetric absorption peaks and modifies dispersion profiles. The study also demonstrates a reduction in the group velocity of the probe, under the effect of the magnetic field, by 1000-fold compared to the speed of light in free space. These giant higher-order nonlinearities, coupled with significantly reduced group velocity, suggest that the LQG system is a quick responder, revealing it as an excellent candidate for terahertz modulation. This also highlights the potential of the system as a promising material for generating and detecting coherent nonlinear signals in the mid-infrared range.
The transient and steady-state behavior of the absorption and the dispersion of a probe pulse laser field propagating through an InGaAs\InP double coupled quantum well are studied. The effect of terahertz radiation excitation, electron tunnelling and incoherent pumping on the optical properties of the probe field is discussed. In the terahertz (30~300 μm or 1~10 THz) intersubband transition, the incoming photon energy is (4~41 mev) and maybe in the order of electron thermal broadening (KT~6 meV-25 meV for 77 K-300 K). Therefore in the conventional structure, the incoming photon can directly excite the ground state electrons to higher energy levels and this process inhabits the correct optical switching in terahertz applications. We show that the group velocity of a light pulse can be controlled from superluminal to subluminal or vice versa by controlling the rates of incoherent pumping field and tunnelling between the quantum wells. The required switching time is calculated and we find it between 3 to 26 picoseconds.
Landau-quantized graphene (LQG) offers a magnetically controlled platform for manipulating coherent inter-Landau-level transitions of Dirac fermions. Such a platform provides compact control of terahertz and infrared photonic signals. Here, a closed-form susceptibility expression is derived using the density-matrix approach, where the real part of the susceptibility describes dispersion and the imaginary part describes absorption or gain. The numerical results show that tuning the control field modifies the probe response from a dispersive resonance regime to a transparency window and a gain-assisted response. The calculated group-index variation, approximately from 0.6 to 1.7, enables broad modulation of the probe group velocity, ranging from about 1.8 × 10 8 m/s to 5.2 × 10 8 m/s . The reduced-absorption region indicates an electromagnetically induced transparency response suitable for controlled probe-field transmission. Distinct spectral features are also observed in the absorption coefficient and electron energy-loss spectrum (ELS), indicating selective energy transfer near the LQG resonance and potential relevance for THz/IR modulation. In addition, the frequency-selective and sign-reversible photon-drag response suggests detuning-controlled optical momentum transfer. These tunable responses within the linear regime support LQG as a reconfigurable medium for quantum optical transport, synchronization, pulse routing, buffering, and chip-scale THz photonic interfaces.