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Journal of Applied Physics

Pulse propagation and optically controllable switch in coupled semiconductor-double-quantum-dot nanostructures

Hamid Reza Hamedi

Published May 12, 2016• 5 citations
Publisher

Abstract

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.

DOI
10.1063/1.4949328

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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.
We theoretically analyze the transient properties of a probe field absorption and dispersion in a coupled semiconductor double-quantum-dot nanostructure. We show that in the presence of the Gaussian laser beams, absorption and dispersion of the probe field can be dramatically influenced by the relative phase between applied fields and intensity of the Gaussian laser beams. Transient and steady-state behaviors of the probe field absorption and dispersion are discussed to estimate the required switching time. The estimated range is between 5–8 ps for subluminal to superluminal light propagation .
We investigate control of the propagation dynamics of weak twin laser pulses and propose a dual-optical switching scheme in four-level semiconductor quantum dots of diamond configuration. It is shown that the propagation dynamics of the two probe pulses depend not only on the intensity of corresponding control field in each cascade transition path but also on the relative intensities of the two control fields. This property provides the probability for realizing all-optical switching in the quantum dots. Possible all-optical switching operations for any one of the probe fields or both probe fields simultaneously with the same or adverse switching status can be realized by modulating the corresponding control fields. In addition, the relative phase of the laser fields also influences the switching operation and can be used to realize optical switching, which is also discussed in the paper.
The tunneling-induced optical properties in weak probe pulse propagation are investigated through a quadruple quantum dot (QQD) molecule composed of a center dot and three satellite dots. The dynamic control of pulse propagation is addressed by solving the Maxwell–Bloch equations for the QQD medium and field simultaneously in space and time. It is found that by properly adjusting the system parameters, an absorptive case for the probe pulse can be switched to a case in which the light pulse propagates without significant absorption for quite a long propagation distance. An analytical solution is presented to comprehend such a controllable switch. Finally, it is shown that it is possible to store and retrieve the probe pulse in such a QQD system through adiabatically varying the tunneling couplings. The proposed scheme may provide a guideline to develop a new type of optical storage device.
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 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 slowdown of optical pulses due to quantum-coherence effects is investigated theoretically for an ``active material'' consisting of InGaAs-based double quantum dot molecules. These are designed to exhibit a long-lived coherence between two electronic levels, which is an essential part of a quantum-coherence scheme that makes use of electromagnetically induced transparency effects to achieve group-velocity slowdown. We apply a many-particle approach based on realistic semiconductor parameters that allows us to calculate the quantum dot material dynamics including microscopic carrier scattering and polarization dephasing dynamics. The group-velocity reduction is characterized in the frequency domain by a quasiequilibrium slowdown factor and in the time domain by the probe-pulse slowdown obtained from a calculation of the spatiotemporal material dynamics coupled to the propagating optical field. The group-velocity slowdown in the quantum dot molecule is shown to be substantially higher than what is achievable from similar transitions in typical InGaAs-based single quantum dots. The dependencies of slowdown and shape of the propagating probe pulses on lattice temperature and drive intensities are investigated.