In this work, we develop a physically transparent Coulomb-interaction model from simplification of a general many-body theory and apply this model to study interacting electron dynamics for transient occupation and quantum coherence in both single and double quantum dots under laser irradiation. Our theory considers self-consistently the Coulomb-renormalized Rabi coupling to light by using an induced optical-depolarization field, corresponding to dynamical exchange interaction between two electrons within the same quantum dot. Meanwhile, we employ evanescent-field coupling for dynamical Coulomb interaction between two electrons in different quantum dots based on a surface-plasmon model. In particular, we explore the quantum interference between a pair of laser-induced quantum coherence in three-level quantum-dot systems, which gives rise to indirect transition of electrons for sum- and difference-frequency transient optical responses. By varying laser frequency detuning, the control of laser-dressed electronic states becomes possible and can be utilized for switching among off-state, partial, and complete on-states. This study will be useful for controlling the phase entanglement of two laser-dressed states of quantum dots, as well as for enhancing the electro-optical performance through sum- and difference-frequency transitions in many optoelectronic devices.
In this work, we develop a physically transparent Coulomb-interaction model from simplification of a general many-body theory and apply this model to study interacting electron dynamics for transient occupation and quantum coherence in both single and double quantum dots under laser irradiation. Our theory considers self-consistently the Coulomb-renormalized Rabi coupling to light by using an induced optical-depolarization field, corresponding to dynamical exchange interaction between two electrons within the same quantum dot. Meanwhile, we employ evanescent-field coupling for dynamical Coulomb interaction between two electrons in different quantum dots based on a surface-plasmon model. In particular, we explore the quantum interference between a pair of laser-induced quantum coherence in three-level quantum-dot systems, which gives rise to indirect transition of electrons for sum- and difference-frequency transient optical responses. By varying laser frequency detuning, the control of laser-dressed electronic states becomes possible and can be utilized for switching among off-state, partial, and complete on-states. This study will be useful for controlling the phase entanglement of two laser-dressed states of quantum dots, as well as for enhancing the electro-optical performance through sum- and difference-frequency transitions in many optoelectronic devices.
In this paper, by applying generalized density-matrix equations, we explore the ultrafast dynamics of photo-generated electron–hole pairs in the system composed of electromagnetically coupled GaAs/AlGaAs quantum dots and reveal the physics mechanism behind laser-controlled nonlinear-optical response of electron–hole pairs. For the single-dot system, we present numerical results to show the transient dependence of carrier occupations and induced quantum coherence of electron–hole pairs in the presence of either a single or double laser pulses, as well as for a step turning-on of the laser field. For a dipole-radiation coupled double-dot system, we study numerically the time dependence of both intradot and interdot self-consistent depolarization fields within and between two dots, respectively. Meanwhile, we further demonstrate the significance of phase matching between induced depolarization fields and incident-laser pulse in order to maximize the stimulated transitions of electron–hole pairs and ensure non-quenched Rabi oscillations in each quantum dot. The employed theoretical model and the associated numerical analysis method are expected to facilitate designing and developing artificial quantum molecules composed of arbitrarily dielectric-embedded quantum dots with non-local quantum interactions and entanglement, as well as optically manipulating electron states of artificial quantum molecules.
We study the effects of a laser on the splitting of the lowest electronic states of a pair of two-dimensional (2D) GaAs-(Ga,Al)As coupled quantum dots, in the presence of a homogeneous external magnetic field. The interaction of light with the 2D quantum dots is treated within a dressed-band approach in which a two-band scheme is used to model the GaAs bulk semiconductor whereas the interaction with the laser field is treated through the renormalization of the semiconductor energy gap and conduction/valence effective masses. This approach is valid far from resonances and has been successfully used to treat other confined semiconductor heterostructures. We focus our attention on the splitting of the lowest singlet and triplet states and on their double occupation probability. We analyze the exchange coupling (J) in the effective Heisenberg model as a function of the laser field and its detuning, as well as of the magnetic field (B) within the Heitler-London approximation of molecular physics. We find that due to the electronic confinement the laser may play a role similar to the external magnetic field in the qualitative behavior of the exchange parameter J. Furthermore, the presence of the laser may assure both the sizable exchange coupling and the vanishingly small double occupation probability required for efficient quantum computer operations, even in the absence of an external magnetic field. Besides being of fundamental interest, these features may be used as an efficient two-qubit gate control.
Atomic phase coherence (quantum interference) in a multilevel atomic gas exhibits a number of interesting phenomena. Such an atomic quantum coherence effect can be generalized to a quantum-dot molecular dielectric. Two quantum dots form a quantum-dot molecule, which can be described by a three-level Λ-configuration model {∣0⟩,∣1⟩,∣2⟩}, i.e., the ground state of the molecule is the lower level |0〉 and the highly degenerate electronic states in the two quantum dots are the two upper levels ∣1⟩,∣2⟩. The electromagnetic characteristics due to the |0〉–|1〉 transition can be controllably manipulated by a tunable gate voltage (control field) that drives the |2〉–|1〉 transition. When the gate voltage is switched on, the quantum-dot molecular state can evolve from one steady state (i.e., |0〉–|1〉 two-level dressed state) to another steady state (i.e., three-level coherent-population-trapping state). In this process, the electromagnetic characteristics of a quantum-dot molecular dielectric, which is modified by the gate voltage, will also evolve. In this study, the transient evolutional behavior of the susceptibility of a quantum-dot molecular thin film and its reflection spectrum are treated by using the density matrix formulation of the multilevel systems. The present field-tunable and frequency-sensitive electromagnetic characteristics of a quantum-dot molecular thin film, which are sensitive to the applied gate voltage, can be utilized to design optical switching devices.
A theory of both linear and nonlinear electromagnetic responses of a single quantum dot (QD) exposed to quantum light, accounting for depolarization induced local field has been developed. Based on the microscopic Hamiltonian accounting for the electron-hole exchange interaction, an effective two-body Hamiltonian has been derived and expressed in terms of the incident electric field, with a separate term describing the QD depolarization. The quantum equations of motion have been formulated and solved using the Hamiltonian for various types of the QD optical excitation, such as Fock qubit, coherent fields, vacuum state of electromagnetic field, and light with arbitrary photonic state distribution. For a QD exposed to coherent light, we predict the appearance of two oscillatory regimes in the Rabi effect separated by the bifurcation. In the first regime, the standard collapse-revival phenomenon does not reveal itself and the QD population inversion is found to be negative, while in the second one, the collapse-revival picture is found to be strongly distorted as compared to that predicted by the standard Jaynes-Cummings model. For the case of QD interaction with an arbitrary quantum light state in the linear regime, it has been shown that the local field induces a fine structure of the absorbtion spectrum. Instead of a single line with frequency corresponding to the exciton transition frequency, a duplet appears, with one component shifted by the amount of the local field coupling parameter. It has been demonstrated that the strong light--matter coupling regime arises in the weak-field limit. A physical interpretation of the predicted effects has been proposed.
We theoretically investigate the influence of dynamic Coulomb interaction on optical bistability and Rabi oscillations in a driven two-level semiconductor quantum dot system under laser irradiation. Using density matrix equations derived from the Coulomb-interaction model proposed by Lu et al. [Phys. Rev. A 103, 043504 (2021)], we obtain analytical solutions for population inversion under the rotating wave approximation. Our analysis shows that the Coulomb interaction induces optical bistability, governed by a cubic equation. The thresholds and the shapes of the hysteresis loops are tunable and can be controlled by various parameters, including electron density, confinement potential, detuning, and dephasing. Additionally, our numerical simulations demonstrate the potential for achieving high-efficiency population inversion and predicting bifurcation and anharmonic regimes in Rabi oscillations under monochromatic excitation.
This work is focused on the optical dynamics of mesoscopic semiconductor heterostructures, using as prototypes zero-dimensional quantum dots and quantum cascade lasers which consist of quasitwo-dimensional quantum wells. Within a density matrix theory, a microscopic many-particle theory is applied to study scattering effects in these structures: the coupling to external as well as local fields, electron-phonon coupling, coupling to impurities, and Coulomb coupling. For both systems, the investigated effects are compared to experimentally observed results obtained during the past years. In quantum dots, the three-dimensional spatial confinement leads to the necessity to consider a quantum kinetic description of the dynamics, resulting in non-Markovian electron-phonon effects. This can be seen in the spectral phonon sidebands due to interaction with acoustic phonons as well as a damping of nonlinear Rabi oscillations which shows a nonmonotonous intensity and pulse duration dependence. An analysis of the inclusion of the self-interaction of the quantum dot shows that no dynamical local field terms appear for the simple two-level model. Considering local fields which have their origin in many quantum dots, consequences for a two-level quantum dot such as a zero-phonon line broadening and an increasing signal in photon echo experiments are found. For the use of quantum dots in an optical spin control scheme, it is found that the dephasing due to the electron-phonon interaction can be dominant in certain regimes. Furthermore, soliton and breather solutions are studied analytically in nonlinear quantum dot ensembles. Generalizing to quasi-two-dimensional structures, the intersubband dynamics of quantum cascade laser structures is investigated. A dynamical theory is considered in which the temporal evolution of the subband populations and the current density as well as the influence of scattering effects is studied. In the nonlinear regime, the scattering dependence and the importance of coherence for Rabi oscillations is investigated. The optically induced charge dynamics is discussed with respect to coherent effects. Calculations of the electronic density and pump-probe signals within a microscopic theory of dephasing show coherent transport effects such as gain oscillations, in agreement with recent experimental results.