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Journal of Physics B Atomic Molecular and Optical Physics

Propagation of a voltage-controlled infrared laser pulse and electro-optic switch in a coupled quantum-dot nanostructure

Jiahua Li, Rong Yu, Liu-Gang Si, Xin‐You Lü, Xiaoxue Yang

Published Feb 23, 2009• 25 citations
Publisher

Abstract

We study infrared-light propagation and dynamical control of a tunable three-level system in a driven quantum-dot (QD) molecule by means of interdot tunnelling instead of a pumping laser. By numerically solving coupled Bloch?Maxwell equations, it is shown that under the resonant tunnelling condition, an interband (IB) infrared-light pulse acting as a 'signal' can propagate with transparency due to the strong tunnelling-induced coupling. However, when the applied bias voltage tilts the energy levels of the structure such that the levels of the different dots move out of resonance (i.e., the nonresonant tunnelling), with an increase of detuning ?12, the coupling efficiency of interdot tunnelling decreases considerably and the IB infrared-light pulse will be almost completely absorbed after a characteristic propagation length. This can work as an absorptive optical switch where a signal (IB infrared light) is fully controlled by the external bias voltage. Our calculations provide a guideline for the development of new types of nanoelectronic devices in the QD solid-state system, which is much more practical than that in an atomic system because of its flexible design and the controllable (tunable) interference strength.

DOI
10.1088/0953-4075/42/5/055509

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Journal of the Physical Society of Japan•Dec 26, 2016•3 citations
We study infrared-light propagation and dynamical control of a tunable three-level system in a driven quantum-dot (QD) molecule by means of interdot tunnelling instead of a pumping laser. By numerically solving coupled Bloch?Maxwell equations, it is shown that under the resonant tunnelling condition, an interband (IB) infrared-light pulse acting as a 'signal' can propagate with transparency due to the strong tunnelling-induced coupling. However, when the applied bias voltage tilts the energy levels of the structure such that the levels of the different dots move out of resonance (i.e., the nonresonant tunnelling), with an increase of detuning ?12, the coupling efficiency of interdot tunnelling decreases considerably and the IB infrared-light pulse will be almost completely absorbed after a characteristic propagation length. This can work as an absorptive optical switch where a signal (IB infrared light) is fully controlled by the external bias voltage. Our calculations provide a guideline for the development of new types of nanoelectronic devices in the QD solid-state system, which is much more practical than that in an atomic system because of its flexible design and the controllable (tunable) interference strength.
The problem of pulse propagation is theoretically investigated through a coupled semiconductor-double-quantum-dot (SDQD) nanostructure. Solving the coupled Maxwell–Bloch equations for the SDQD and field simultaneously, the dynamic control of pulse propagation through the medium is numerically explored. It is found that when all the control fields are in exact resonance with their corresponding transitions, a weak Gaussian-shaped probe pulse is transmitted through the medium nearly without any significant absorption and losses so that it can preserve its shape for quite a long propagation distance. In contrast, when one of the control fields is not in resonance with its corresponding transition, the probe pulse will be absorbed by the QD medium after a short distance. Then we consider the probe pulses with higher intensities. It is realized that an intense probe pulse experiences remarkable absorption and broadening during propagation. Finally, we demonstrate that this SDQD system can be employed as an optically controllable switch for the wave propagation to transit from an absorbing phase to a perfect transparency for the probe field. The required time for such switch is also estimated through realistic values.
Since discrete multilevel transitions of quantum-dot molecules driven by external electromagnetic fields can exhibit quantum coherence effects, such an optical characteristic can be utilized to control propagation of electromagnetic wave through a quantum-dot molecule dielectric film. Since inner-dot tunneling in quantum-dot molecules can be controlled by a gate voltage, destructive quantum coherence among multilevel transitions in quantum-dot molecule would give rise to EIT (electromagnetically induced transparency). In this report, we shall investigate controllable on- and off-resonance tunneling effects of an incident electromagnetic wave through such a quan-tum-dot-molecule dielectric film, of which the optical response is tuned by the switchable gate voltage. We have found from the theoretical mechanism that a high gate voltage can cause the EIT phenomenon of quan-tum-dot-molecule systems, and under the condition of on-resonance light tunneling through the thin film, the probe field will propagation without loss if the probe frequency detuning is zero. By taking advantage of these effects sensitive to the tunable gate voltage, such quantum coherence would be inte-grated in certain photonic structures, and some devices such as photonic switching and transistors can be designed. Transient evolution of optical characteristics in the quantum-dot-molecule dielectric film (once the tunable gate voltage is turned on or off) is also considered in this report.
Abstract Based on a GaAs/AlGaAs quadruple-coupled quantum dot heterostructure, an optical switch for controlling superluminal and subluminal light propagation is suggested. The transient and steady state behaviour of the absorption and dispersion of a probe pulse laser field through a quadruple quantum dot molecule are studied. We show that the group velocity of a light pulse can be controlled from superluminal to subluminal, or vice versa, by controlling the tunnelling rates between the quantum dots. The required switching time is calculated and we find it to be about 8 ps. We also investigated a method for the all-optical switching of probe field absorption from a large amount to nearly zero just by applying an incoherent pumping field. We estimated the required switching time for this case to be between 3 and 14 ps.
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.
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.
Quantum-dot-molecular phase coherence (and the relevant quantum-interference-switchable optical response) can be utilized to control electromagnetic wave propagation via a gate voltage, since quantum-dot molecules can exhibit an effect of quantum coherence (phase coherence) when quantum-dot-molecular discrete multilevel transitions are driven by an electromagnetic wave. Interdot tunneling of carriers (electrons and holes) controlled by the gate voltage can lead to destructive quantum interference in a quantum-dot molecule that is coupled to an incident electromagnetic wave, and gives rise to a quantum coherence effect (e.g., electromagnetically induced transparency, EIT) in a quantum-dot-molecule dielectric film. The tunable on- and off-resonance tunneling effect of an incident electromagnetic wave (probe field) through such a quantum-coherent quantum-dot-molecule dielectric film is investigated. It is found that a high gate voltage can lead to the EIT phenomenon of the quantum-dot-molecular systems. Under the condition of on-resonance light tunneling through the present quantum-dot-molecule dielectric film, the probe field should propagate without loss if the probe frequency detuning is zero. Such an effect caused by both EIT and resonant tunneling, which is sensitive to the gate voltage, can be utilized for designing devices such as photonic switching, transistors, and logic gates.