Triple Quantum Dot Molecule Research Articles

Adjusting amplitude of the stored optical solitons by inter-dot tunneling coupling in triple quantum dot molecules

We study the propagation properties of a probe field in an aligned asymmetric triple quantum dot molecule with both sides inter-dot tunneling coupling effect. It is shown that the probe field can form optical soliton due to the destructive quantum interference induced by the quantum inter-dot tunneling coupling effect. Interestingly, these optical solitons can be stored and retrieved by adjusting single or double inter-dot tunneling coupling effect, different from that light memory in the ultra-cold atom system. Furthermore, we also find that the amplitude of the stored optical soliton can be adjusted by the strength of the single or double inter-dot tunneling coupling. It is possible to improve the stability and the fidelity of the optical information in the process of the storage and retrieval in semiconductor quantum dots devices.

Pauli spin blockade in a resonant triple quantum dot molecule

A Pauli spin blockade in quantum dot systems occurs when the charge transport is allowed only for some spin states, and it has been an efficient tool in spin-based qubit devices in semiconductors. We theoretically investigate a Pauli spin blockade in a triple quantum dot molecule consisting of three identical quantum dots in a semiconductor in the presence of an external magnetic field through the molecule. When the three-electron state is on resonance with two- or four-electron states, the Aharonov–Bohm oscillation and the Zeeman splitting lead to a periodic spin blockade effect. We focus on the spin blockade at a two- and three-electron resonance and show that we can tune the magnetic field to selectively allow only either a spin-singlet or spin-triplet state to add an additional electron from tunnel-coupled leads. This spin blockade maintains the three quantum dots at the optimal sweet spot against the charge noise, demonstrating its potential as an efficient readout scheme for the qubits in quantum dot systems.

Controllable storage and retrieval of optical solitons in triple quantum dot molecules by inter-dot tunneling coupling effect

We study the storage and retrieval of the optical field in an aligned asymmetric triple quantum dot molecule with both sides inter-dot tunneling coupling effect. It is shown that the optical solitons can be stored and retrieved by manipulating two inter-dot tunneling coupling effect, different from light memory in the ultra-cold atom system. Furthermore, the amplitude of the optical soliton emerges a trend of first decreasing and then increasing with the increasing strength of the two inter-dot tunneling coupling. It is possibility to improve the fidelity of the storage and retrieval of the optical information in semiconductor quantum dots devices.

Spatial-dependent quantum dot-photon entanglement via tunneling effect

Utilizing the vortex beams, we investigate the entanglement between the triple-quantum dot molecule and its spontaneous emission field. We present the spatially dependent quantum dot-photon entanglement created by Laguerre-Gaussian (LG) fields. The degree of position-dependent entanglement (DEM) is controlled by the angular momentum of the LG light and the quantum tunneling effect created by the gate voltage. Various spatial-dependent entanglement distribution is reached just by the magnitude and the sign of the orbital angular momentum (OAM) of the optical vortex beam.

Controlling optical properties and drag of photon and surface plasmon polaritons in triple quantum dot molecules and dots-metal plasmonic interface via tunneling-assisted quantum coherence

Optical properties of surface plasmon polaritons (SPPs) and drag of photon and SPPs attracted great attention owing to multi-fold potential fundamental and technological implications. In this paper, we investigate the nature of light propagation, optical properties of probe field and SPPs and drag of photon and SPPs in a four-level triple quantum dot molecule (TQDM) well and a dots-metallic plasmonic interface (DMPI). The quantum coherence in TQDM and coupled DMPI interface is achieved via interbands tunneling-assisted quantum coherence namely- classical electromagnetically induced transparency (EIT) and plasmonic induced transparency (PIT). In contrast to earlier studies, herein we employed Drude-model type dielectric constant of metal with inclusion of size-dependent correction term to account for the reduced electron relaxation rate near the thin metal interface. In particular, after solving the master density-matrix equation of the quantum dot system for the eigenvalues, we interpreted the calculated theoretical results on light dragging and optical properties of probe field and SPPs via tunneling-assisted dressed-state picture of EIT/PIT in the proposed TQDM system and DMPI interface. The tunneling parameter considerably tuned the nature of light propagation from subluminal to superluminal and vice versa, optical properties and drag of photon and SPPs. The maximum positive (negative) value of the group index for photon is of order 3.68×106 (2.685×106) while for SPPs it is of order 3×105. The maximum value of lateral drag for photon and SPPs is ±5×10-2m and ±1.173×10-3m, respectively. The calculated propagation length and wavelength for SPPs are 6.25×10-7m and 3.78×10-7 m which correspond to the quality factor of 10.38.

Nonlinear dynamics of triple quantum dot molecules in a cavity: multi-stability of three types of cavity solitons

By numerical simulation of a cavity filled with triple quantum dot molecules under tunneling induced transparency, we show that various regimes of existence of different kinds of cavity solitons are possible. Forming in overlapping regions of a multistable parameter space, cavity solitons in this system exhibit different dynamical behaviors: stationary on a flat background when there is only one cavity soliton branch, oscillating when two cavity soliton branches coexist, and stationary-rambling on a honeycomb background arising from simultaneous presence of a stable pattern and a cavity soliton branch. In particular, we show that three different types of dissipative localized structures can be excited in multistable regions where material coherence is high due to light-matter interaction processes.

Controllable double tunneling induced optical soliton storage in linear triple quantum dot molecules

We propose an asymmetric linear triple quantum dot molecule model for a recent experimental device with a double neighboring dot-dot tunneling coupling, of which the linear and nonlinear dynamical properties are analytically studied by using an amplitude variable approach combined with multi-scale method. It is shown that double transparency windows are formed by the double tunneling coupling. Both dark and bright optical solitons are then obtained, of which both the types and the propagating velocity can be controlled by the two tunneling coupling strengths. Interestingly, the propagating velocity of the solitons can approach to zero at certain tunneling coupling strengths, the motionless optical solitons appearing there. The results indicate potential applications of the semiconductor quantum devices for optical soliton storage.

Relocalization switch in a triple quantum dot molecule in 2D

A symmetric chain of three quantum dots (i.e., one of the simplest quantum dot molecules) is constructed using a three-parametric non-separable version of an asymptotically separable sextic polynomial potential [Formula: see text]. The probability density [Formula: see text] (admitting either the central or off-central dominance) is assumed measured. A dynamical regime is found with an enhanced sensitivity of the central—off-central transition to the parameters. Quantitatively, the possibility of control of such a switch alias “relocalization catastrophe” is illustrated non-numerically.

Scenarios of local spectral property and multifunctional spin selecting for a triple quantum dot molecule: How do the bonding and antibonding orbitals contribute to the spin currents?

Molecular electronic device is considered as a promising candidate for next generation electronic component, where the basic challenge involves understanding the charge and spin transports through molecular objects. In this paper, with the help of the sophisticated numerical renormalization group technique, we study theoretically the spin selective transport in a parallel triple quantum dot molecular device pierced by a local magnetic field along z axis. Based on simplified parameters of real molecular system, we find such device acts as a multifunctional spin selector when the inter-molecule tunneling couplings are asymmetric, including two 100% polarized spin-up summits, and one 100% spin-down summit in the linear conductance. We show in detail the local density of states for the bonding and anti-boding orbitals, and attribute the spin selection to the orbital polarized Coulomb blockade effect. We demonstrate our numerical results are consistent with those estimated by the analytical techniques, including the Friedel sum rule and the energy level crossings of the isolated orbitals.

Dark states in spin-polarized transport through triple quantum dot molecules

We study the spin-polarized transport through a triple quantum dot molecule weakly coupled to ferromagnetic leads. The analysis is performed by means of the real-time diagrammatic technique including up to the second order of perturbation expansion with respect to the tunnel coupling. The emphasis is put on the impact of dark states on spin-resolved transport characteristics. It is shown that the interplay of coherent population trapping and cotunneling processes results in a highly nontrivial behavior of the tunnel magnetoresistance, which can take negative values. Moreover, a super-Poissonian shot noise is found in transport regimes where the current is blocked by the formation of dark states, which can be additionally enhanced by spin-dependence of tunneling processes, depending on magnetic configuration of the device. The mechanisms leading to those effects are thoroughly discussed.

Spin-Seebeck effect and spin polarization in a multiple quantum dot molecule

In this work, we study the conductance and the thermoelectric properties of a quantum dot embedded between two metallic leads with a side-coupled triple quantum dot molecule under a magnetic field. We focus on the spin polarization and thermoelectric quantities. Our results show the possibility of design an efficient spin filter device besides a noticeable enhancement of the Seebeck coefficient driven by the asymmetry in the quantum dots energy levels and a tunable pure spin Seebeck effect is obtained. This behavior also holds in the interacting case, where a pure spin Seebeck effect can be obtained for fixed values of the embedded quantum dot energy level. Our findings could lead to the implementation of a new pure spin energy conversion and capable spin filter devices working with weak magnetic fields.

Study of Goos–Hänchen shifts of partially coherent light fields using a triple quantum dot system in the presence of giant Kerr nonlinearity

The coherent coupling between three quantum dots via tunneling fields leads to double tunneling-induced transparency and giant Kerr nonlinearity with vanishing absorption. This creates the possibility to achieve self-phase modulation in semiconductor nanostructures via controllable tunneling under the conditions of low light levels. As a result, a considerably high refractive index can be obtained. We suggest an intracavity medium which consists of triple quantum dot molecules to control the Goos–Hanchen (GH) shifts in the reflected light. For a suitable design of a triple quantum dot system, our results show that relatively large positive and negative GH shifts are achievable, without significant distortion, using partially coherent incident light fields.

Giant Kerr nonlinearity via tunneling induced double dark resonances in triangular quantum dot molecules

A scheme for giant Kerr nonlinearity via tunneling in triangular triple quantum dot molecules is proposed. In such a system, the linear absorption and the Kerr nonlinearity depend critically on the energy splitting of the excited states and the tunneling intensity. With proper parameters, giant Kerr nonlinearity accompanied by vanishing absorption can be realized. The enhancement of Kerr nonlinearity is attributed to the interacting double dark resonances induced by the tunneling between the quantum dots, requiring no extra coupling laser fields.

Electrical and optical control of entanglement entropy in a coupled triple quantum dot system

We investigated theoretically the entanglement creation through tunneling rate and fields in a four-level triple quantum dot molecule based on InAs/GaAs/AlGaAs heterostructure in both steady state and transient state. We demonstrate that the entanglement entropy among the QDM and its spontaneous emission fields can be controlled by coherent and incoherent pumping field and tunnel-coupled electronics levels. The results may provide some new possibilities for technological applications in solid-state quantum information science, quantum computing, teleportation, encryption, compression codec, and optoelectronics.

Optical bistability in triple quantum dot molecules in weak tunneling regime

We investigated the optical bistability of a triple quantum dot molecule under coherent excitation and considering the spontaneous exciton decay and pure dephasing as two decoherence channels. By manipulating the laser detuning, electric field, and tunneling coupling, the threshold value and the hysteresis cycle width of OB can easily be controlled. Our scheme opens the possibility to control OB with electric gates, which are very useful in building all-optical switches and logic-gate devices for optical computing and quantum information processing.

Control of the entanglement between triple quantum dot molecule and its spontaneous emission fields via quantum entropy

The time evolution of the quantum entropy in a coherently driven triple quantum dot molecule is investigated. The entanglement of the quantum dot molecule and its spontaneous emission field is coherently controlled by the gate voltage and the rate of an incoherent pump field. The degree of entanglement between a triple quantum dot molecule and its spontaneous emission fields is decreased by increasing the tunneling parameter.

Controlling optical bistability via interacting double dark resonances in linear quantum dot molecules

The behavior of optical bistability (OB) in linear triple quantum dot molecules (QDMs) using double tunneling coupling by means of a unidirectional ring cavity is investigated. The linear and nonlinear susceptibilities of the system are also investigated. The double tunneling between the quantum dots can induce the interaction of double dark resonances, which can enhance the nonlinear response of the system. The type, the hysteresis loop, and the threshold of OB can be controlled by the intensity of the double tunneling and the detuning of the probe field. Our results give insights for future experiments and applications in optics using QDMs. (C) 2014 Optical Society of America

Electrical and optical control of optical gain in a coupled triple quantum dot system operating in telecommunication window

We investigate the light amplification and gain without inversion (GWI) in triple quantum dot molecules in both steady-state and transient state. We demonstrate that the light amplification and GWI of a light pulse can be controlled through the rates of the incoherent pumping and tunneling between electronic levels. The required switching times for switching of a light pulse from absorption to gain and vice versa is then discussed. We obtain switching time at about 40 ps, which resembles a high-speed optical switch in nanostructure. The proposed approach in QDMs may provide some new possibilities for technological applications in optoelectronics and solid-state quantum information science.

Cavity linewidth narrowing by tunneling induced double dark resonances in triple quantum dot molecules

A scheme for obtaining a tunable ultranarrow cavity transmission controlled by two tunneling in triple quantum dots system is proposed. In such system, the tunneling can induce double dark resonances, resulting in the appearance of two transparency windows. With the steep dispersion within the narrowed transparency windows, an ultranarrow transmission peak can be obtained, compared with that of double quantum dots system. Furthermore, by varying the energy splitting, the linewidth and the position of the ultranarrow transmission peak can be engineered. Because no coupling laser is required, the scheme proposed here is more convenient for future experiments and applications in optics, and may be useful in designing novel optoelectronic devices.

Tunneling induced dark states and the controllable resonance fluorescence spectrum in quantum dot molecules

Optical spectroscopy, a powerful tool for probing and manipulating quantum dots (QDs), has been used to investigate the resonance fluorescence spectrum from linear triple quantum dot molecules controlled by tunneling, using atomic physics methods. Interesting features such as quenching and narrowing of the fluorescence are observed. In such molecules the tunneling between the quantum dots can also induce a dark state. The results are explained by the transition properties of the dressed states generated by the coupling of the laser and the tunneling. Unlike the atomic system, in such quantum dot molecules quantum coherence can be induced using tunneling, requiring no coupling lasers, which will allow tunneling controllable quantum dot molecules to be applied to quantum optics and photonics.