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Chinese Physics B

High-efficiency asymmetric diffraction based on PT-antisymmetry in quantum dot molecules

Guangling Cheng, Yongsheng Hu, Wenxue Zhong, Aixi Chen

Published May 24, 2021• 6 citations
Publisher

Abstract

Abstract We present preparation of asymmetric grating with higher diffraction efficiency in quantum dot molecules by combining the tunneling effect and parity-time antisymmetry. In the presence of tunneling between two quantum dots, the system exhibits the striking PT antisymmetry via spatially modulating the driving field and the detuning with respect to the driven transition. For this reason, the asymmetric grating could be achieved. The results show that the diffraction efficiency can be adjustable via changing the driving intensity, detuning, tunneling strength, and interaction length, and then the high-order diffraction can be reached. The scheme provides a feasible way to obtain the direction-controlled diffraction grating, which can be helpful for optical information processing and realization of controllable optical self-image.

DOI
10.1088/1674-1056/ac0422

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Abstract We present preparation of asymmetric grating with higher diffraction efficiency in quantum dot molecules by combining the tunneling effect and parity-time antisymmetry. In the presence of tunneling between two quantum dots, the system exhibits the striking PT antisymmetry via spatially modulating the driving field and the detuning with respect to the driven transition. For this reason, the asymmetric grating could be achieved. The results show that the diffraction efficiency can be adjustable via changing the driving intensity, detuning, tunneling strength, and interaction length, and then the high-order diffraction can be reached. The scheme provides a feasible way to obtain the direction-controlled diffraction grating, which can be helpful for optical information processing and realization of controllable optical self-image.
We present an alternative scheme for the preparation of the phase grating in quantum-dot molecules, where the tunnel coupling occurs between two quantum dots. In the presence of interdot tunneling, the nonlinear dispersion can be significantly enhanced with nearly vanishing linear and nonlinear absorption due to the tunneling-induced quantum coherence. With the help of a standing-wave control field, the weak probe light could be diffracted into high-order direction. It is shown that parameters such as the weak-driving intensity, driving detuning, tunneling strength, and interaction length could be used to adjust the diffraction intensity effectively. Our scheme is focused on the weak standing-wave driving and weak tunneling strength, which may provide an easy and actual way to obtain the phase grating and may have potential applications in quantum-optics and quantum-information-processing devices in the solid-state system.
Abstract The scheme for gain-phase grating is proposed via double tunneling effect in the quantum dot molecules system with five-level structure, which is formed by two quantum dots due to inter-dot tunneling. Combining the stranding-wave control field with the double tunneling effect, the weak probe field could be diffracted to the high-order direction with the strong diffraction intensity. In the presence of double tunneling, the gain accompanied with the certain dispersion occurs, which is responsible for the preparation of the high-efficiency grating. It is found that the first-, second-, and other-order diffraction intensities are simultaneously higher than the central intensity and the diffraction intensities could be controlled by adjusting the parameters such as tunneling intensities, interaction length, probe detuning, relative phase and Rabi frequencies of external fields. The scheme we present can be utilized to develop a new photonic device for optical network and communication.
Abstract We propose a theoretical scheme for realizing a two-dimensional (2D) asymmetric diffraction grating in a four-level quantum dot molecules (QDMs) system with double tunneling effects. The QDMs system interacts with a weak probe field, a 2D SW control field and a composite Laguerre–Gaussian (LG) vortex field. By adjusting system parameters such as the orbital angular momentum (OAM) number, the beam waist parameter of the vortex light, the tunneling strength, and the detuning of the standing-wave (SW) field, the energy distribution and the diffraction intensity of the probe field can be controlled effectively. In addition, the detuning of the probe field can be used to achieve the symmetrical switching control of the 2D diffraction grating between the second and the fourth quadrants. This investigation may have potential application in beam splitting technology and optical device design.
Quantum dot molecules (QDMs), with their unique optoelectronic properties derived from quantum confinement and tunneling effects, are not only promising for advanced photonic applications but also provide the intrinsic advantage of nanoscale dimensions, which is critical for integrated miniaturized devices. In this work, we propose a scheme to realize a high-intensity two-dimensional asymmetric electromagnetically induced diffraction grating in a QDMs system by incorporating spontaneously generated coherence (SGC) and dual tunneling channels. Our theoretical analysis shows that the presence of SGC markedly enhances the intensity and efficiency of higher-order diffractions. Furthermore, by adjusting the orbital angular momentum and beam waist of vortex beams, we not only amplify the disparity in asymmetric diffraction and enhance the efficiency of the third-order diffraction peak, but also enable a lossless spatial interchange between the diffraction peak positions and those at symmetric positions solely by reversing the orbital angular momentum direction. Additionally, tuning the interdot tunneling strength increases the maximum third-order diffraction intensity by three orders of magnitude, reaching an intensity that is more than ten times higher than the third-order diffraction intensity observed at symmetric positions. These results, which fully leverage the nanoscale advantage and tunable characteristics of QDMs, offer a solid foundation for the implementation of compact photonic devices and pave the way for potential applications in optical diffractive neural networks and electromagnetically induced quantum holography.
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.
Abstract We present a theoretical scheme to realize two-dimensional (2D) asymmetric diffraction grating in a five-level inverted Y-type asymmetric double semiconductor quantum wells (SQWs) structure with resonant tunneling. The SQW structure interacts with a weak probe laser field, a spatially independent 2D standing-wave (SW) field, and a Laguerre–Gaussian (LG) vortex field, respectively. The results indicate that the diffraction patterns are highly sensitive to amplitude modulation and phase modulation. Because of the existence of vortex light, it is possible to realize asymmetric high-order diffraction in the SQW structure, and then a 2D asymmetric grating is established. By adjusting the detunings of the probe field, vortex field, and SW field, as well as the interaction length, diffraction intensity, and direction of the 2D asymmetric electromagnetically induced grating (EIG) can be controlled effectively. In addition, the number of orbital angular momenta (OAM) and beam waist parameter can be used to modulate the diffraction intensity and energy transfer of the probe light in different regions. High-order diffraction intensity is enhanced and high-efficiency 2D asymmetric diffraction grating with different diffraction patterns is obtained in the scheme. Such 2D asymmetric diffraction grating may be beneficial to the research of optical communication and innovative semiconductor quantum devices.