We consider the coupling effect between interdot tunneling coupling and external optical control field to study the linear optical property and the formation of temporal optical solitons in a quantum dot molecules system, analytically. The results show that the double tunneling induced transparency (TIT) windows are appeared in the absorption curve of probe field because of the formation of dynamic Stark splitting and quantum destructive interference effect from the two upper levels. Interestingly, the width of the TIT window becomes wider with the increasing intensity of the optical control field. We also find that the Kerr nonlinear effect of the probe field can be modulated effectively through coherent control both the control field and the interdot tunneling coupling in this system. Meanwhile, we demonstrate that the formation of dark or bright solitons can be practical regulated by varying the intensity of the optical control field.
We consider the coupling effect between interdot tunneling coupling and external optical control field to study the linear optical property and the formation of temporal optical solitons in a quantum dot molecules system, analytically. The results show that the double tunneling induced transparency (TIT) windows are appeared in the absorption curve of probe field because of the formation of dynamic Stark splitting and quantum destructive interference effect from the two upper levels. Interestingly, the width of the TIT window becomes wider with the increasing intensity of the optical control field. We also find that the Kerr nonlinear effect of the probe field can be modulated effectively through coherent control both the control field and the interdot tunneling coupling in this system. Meanwhile, we demonstrate that the formation of dark or bright solitons can be practical regulated by varying the intensity of the optical control field.
Considering the exciton-biexciton coherence, we analytically study the linear absorption and nonlinear propagation properties of the probe and signal field in a semiconductor quantum dot. It is found that in the linear case, in the system takes place an electromagnetically induced transparency phenomenon. Furthermore, we obtain that in the system there occurs one- or two-transparency window, or optical gain, which is controlled by adjusting the coupling control field. For the nonlinear case, the weak probe field, which is induced by a signal field, splits into two parts. When their excited self-Kerr and cross-Kerr nonlinear effects balance the refractive effect of the beam, the system exhibits bright-bright, bright-dark, dark-bright, dark-dark soliton pairs.
In the present work, the linear and nonlinear optical properties of quantum dot molecules composed of two quantum dots as well as three quantum dots molecules, respectively known as double quantum dot (DQD) molecule and triple quantum dot (TQD) molecules are studied using the probability amplitude method, and the obtained results are discussed and compared. By solving the state equations of these systems in the interaction picture, under the rotating wave approximation and the dipole approximation, the first and third-order susceptibilities for DQD and TQD molecules are calculated. A phenomenon called tunneling-induced transparency (TIT) which is similar to electromagnetically induced transparency (EIT) is studied in these types of quantum dot molecules. The effect of key system parameters such as tunneling couplings between quantum dots and the tunneling intensity on the linear and nonlinear optical response of multiple quantum dot molecules DQD and TQD is investigated. It was shown that the position and the width of the TIT window created in these quantum dot molecules can be tuned by changing the physical parameters.
We manipulate the coupling effect between interdot tunneling and the external control field to study the optical diffractive property in a quantum dot molecule (QDM) system. Based on the density matrix approach, an analytical relation is obtained for the optical susceptibility, which shows tunneling-induced transparency (TIT) in the absorption spectra. We propose an innovative optoelectronic device called tunneling-induced grating, which operates based on the diffraction of the forward-transmitted probe laser light. The diffraction integrals for the far-field regime (i.e., Fraunhofer diffraction) are numerically solved, and the effect of interdot tunneling coupling strength on the diffraction patterns is studied. It is shown that the transmission is increased under tunneling-induced quantum coherence. The weak probe light can be diffracted into higher-order directions upon applying a standing-wave control field. The optimal parametric condition for maximum first- and second-order diffractions is obtained. The results find the potential applications in quantum information processing devices, such as all-optical grating and switches at low light levels.
A scheme for giant enhancement of the Kerr nonlinearity in linear triple quantum dot molecules is proposed. In such a system, the tunneling-induced transparency window obtained in double quantum dot molecules splits into two windows, due to the coupling with the third quantum dot. And most important, the Kerr nonlinearity can be enhanced by several orders of magnitude, compared with that generated in double quantum dot molecules. With proper detuning of the tunneling, giant Kerr nonlinearity accompanied by vanishing absorption can be realized, which opens the possibility to enhance self-phase modulation in tunneling controllable semiconductor nanostructures under conditions of low light levels. Quantitative analysis shows that the giant Kerr nonlinearity is attributed to the interacting double dark resonances induced by the tunneling between the triple quantum dots, therefore no extra laser fields are required.
Soliton, which can travel over long distance without attenuation or shape change due to the balance of the interplay between dispersion (or diffraction) and nonlinearity in nonlinear medium, becomes a good information carrier in quantum information processing and transmission. Up to now, the study on the optical solitons mainly focuses on ultra-cold atomic electromagnetic induction transparency (EIT) medium. This is mainly because ultra-cold atomic system can generate strong nonlinear effect under low light excitation. However, for the practical application, it is a big challenge to control accurately the optical soliton dynamics in the atomic EIT medium due to its low temperature (which approaches to absolute zero) and rarefaction. Fortunately, with the maturity of semiconductor quantum production technology, quantum dots have extensive application prospect in quantum information processing and transmission. So, in the paper, we study the optical soliton dynamics in a four-level asymmetric array-type three-quantum-dot EIT medium. Based on the current experimental results, we first propose a four-level asymmetric array-type three-quantum-dot EIT model. Subsequently, by using amplitude variable approach combined with multi-scale method, we study analytically the propagation of a probe pulse in this system. It is shown that when one (the another) inter-dot tunneling coupling is turned on (off), only a single transparency window appears in the center range of the probe field detuning. Only if two inter-dot tunneling couplings are turned on will two transparent windows be distributed on both sides of the central region of the probe field detuning. And the width of the single transparent window or the widths of two transparent windows become wider with the strength of the inter-dot tunneling coupling increasing. For the nonlinear case, by choosing appropriate parameters in the area of the transparency window, the stable propagation of soliton can be realized. Interestingly, we find that the strength of the inter-dot tunneling coupling has an important effect on the soliton dynamic behaviors. In the case that one (the another) inter-dot tunneling coupling is turned on (off), with the increase of strength of the inter-dot tunneling coupling, the velocity of the soliton exhibits a trend of first increasing and then decreasing, and the amplitude of the soliton presents a increasing trend for ever. For the case that two inter-dot tunneling couplings are turned on, with the strength of the two inter-dot tunneling coupling increasing, the velocity of the soliton presents a decreasing trend for ever, while the amplitude of the soliton exhibits a trend of first decreasing and then increasing. Thus, the amplitude modulation effect of optical soliton can be realized in semiconductor quantum dot devices.
We have investigated the nonlinear interaction between a weak-pulsed probe field and a four-level Y-type atomic system with dual ladder-type electromagnetically induced transparency. Two strong coupling fields induce a quantum destructive interference effect which depletes the population in the two nearly degenerate uppermost levels of the system and dramatically enhances the linear as well as nonlinear dispersion while simultaneously significantly suppressing the probe field absorption. We present the semiclassical quantum analysis of the system. The perturbation method of multiple scales is used to derive a differential envelope equation that describes the propagation of the probe field in the Y-type atomic system. It is then demonstrated that bright and dark optical solitons can be formed in this system.