Coupled Semiconductor Quantum Research Articles

Exploring the Impact of Weak Measurements on Exciton-Exciton Interactions

Abstract In our study of super quantum discord between two excitonic qubits inside a coupled semiconductor quantum dots system, our primary focus is to uncover the impact of weak measurement on its quantum characteristics. To achieve this, we analyze how varying the measurement strength x, affects this super quantum correlation in the presence of thermal effects. Additionally, we assess the effect of this variation on the system’s evolution against its associated quantum parameters; external electric fields, exciton-exciton dipole
interaction energy and Förster interaction. Our findings indicate that adjusting x to smaller values effectively enhances super quantum correlation, making weak measurements act as a catalyst. This adjustment ensures its robustness against thermal effects while preserving the non-classical attributes of system. Furthermore, our study unveils that the effect of weak measurements on this
latter surpasses the quantum effects associated with the system. Indeed, manipulating the parameter x allows weak measurement to function as a versatile tool for modulating quantum characteristics and controlling exciton-exciton interactions within the coupled semiconductor quantum dots system.

Plasmonically coupled semiconductor quantum dots for efficient hydrogen photoelectrocatalysis

Photocatalytic water splitting has attracted significant attention as a low-cost, clean, and green method for the conversion of solar energy into hydrogen, highlighting its potential to solve energy and environmental problems. In this work, we report the coupling of a plasmonic resonator with semiconductor quantum dots (QDs) for enhancement in photoelectrocatalytic water splitting toward hydrogen (H2) production. Specifically, cadmium selenide (CdSe) QDs were deposited on silver nano-gratings (Ag gratings). Plasmonic enhancement was observed in the absorption/emission of QDs using our angle-resolved steady-state optical spectroscopy. Furthermore, angle-resolved absorption spectra helped us to optimize the illumination conditions for resonant excitation using a setup for photoelectrochemical (PEC) experiments. Under the resonant pump, the emission of the QDs has been plasmonically enhanced with a Purcell factor (FP) of ∼1.5. Our numerical simulation revealed a strong near-field enhancement due to the excitation of surface plasmon resonances, contributing to FP. A similar enhancement order in the PEC experiments was also observed under resonant pump conditions, indicating the contribution of plasmon resonances to the enhanced photoelectrocatalysis. Switching the excitation's polarization further reinforces this, resulting in an enhanced photocurrent under p-polarization. These findings provide a proof of concept, thus laying the foundation for a practical device for efficient solar-to-H2 conversion.

Measurement of Tunnel Coupling in a Si Double Quantum dot Based on Charge Sensing

Tunnel coupling is a key parameter in coupled semiconductor quantum dots, and is a crucial ingredient in various device applications, such as exchange gates and spin shuttling in quantum information processing. A widely used charge-sensing technique to extract the tunnel coupling of a double quantum dot accounts for only the ground orbital state in each dot, but the authors show that in a Si double dot, valley-orbit coupling must be included in the analysis. With their more complete model, one can not only extract the $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}v\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}y$ (ground-state) tunnel coupling more accurately, but also obtain information on $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}v\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}y$ (ground-to-excited-state) tunnel coupling.

Wigner Function as a Detector of Entanglement in Open Two Coupled InAs Semiconductor Quantum Dots

Wigner Function as a Detector of Entanglement in Open Two Coupled InAs Semiconductor Quantum Dots

Robustness of Wigner function negativity under the exciton-exciton interaction effects inside two coupled semiconductor quantum dots

We analyze theoretically the Wigner function negativity for thermal density matrix of analogous and equidistant two coupled semiconductor quantum dots at different temperatures. In this respect, we explore the quantum influences of the temperature, the external electric field, the Forster interaction and the exciton-exciton dipole interaction energy on its behavior. In particular, we show that the negativity of wigner function still survives for large values of temperature ensuring that the non-classicality of the two coupled semiconductor quantum dots system does not get lost under thermal effect. Moreover, we show that this negativity is hypersensitive to the external electric field effect, nevertheless, its sensitivity to this effect is extensively perturbed for higher values of Forster interaction, temperature and exciton-exciton dipole interaction energy. Further, we show that increasing this latter enhances the quantumness of system as the negativity of wigner function also increases.

Plasmon effects in the two-photon Rabi oscillations in a strongly coupled semiconductor quantum dot–metal nanoshell composite

We theoretically study two-photon Rabi oscillations (TPRO) in a nanocomposite comprising a semiconductor quantum dot (SQD) strongly coupled to a metallic nanoshell (MNS), which undergoes a pulsed excitation. The SQD is modeled as a three-level ladder-like quantum system (ground, one-exciton, and bi-exciton states). Its optical dynamics is described quantum-mechanically within the density matrix formalism framework, while the MNS is treated classically through its frequency-dependent polarizability. We find two effects of the presence of a MNS in close proximity to the SQD: (a) - a sufficient increase of the number of Rabi cycles as compared to the case of an isolated SQD and (b) - incoherent population of the one-exciton state giving rise to the destruction of the TPRO.

Quantum correlations dynamics in two coupled semiconductor InAs quantum dots

We investigate the dynamics of both quantum discord and concurrence within two excitonic qubits embedded in two coupled semiconductor quantum dots independently interacting with dephasing reservoirs. Their behavior in both Markovian and non-Markovian environments is explored against the dimensionless time and the temperature. Moreover, the effects of the external electric field on these correlations as well as the effects related to the Förster interaction are extensively analyzed. We show that the non-Markovian behavior of quantum correlations is always preserved under the variation of the electric field and the Förster interaction, regardless of the strong influence of these two parameters on the amount of quantum correlations. Furthermore, we show that nonzero discord can still be observed for large values of temperature and dimensionless time, unlike concurrence which vanishes in this regime.

Control of Self-Kerr Nonlinearity in a Driven Coupled Semiconductor Quantum Dot–Metal Nanoparticle Structure

The self-Kerr nonlinear optical response of a probe field is investigated in the presence of a near-resonant pump field in coupled metal nanoparticle (MNP)–semiconductor quantum dot (SQD) nanostructures. The study of the spectra is based on the solution of the resulted density matrix equations for the case of a colloidal CdSe-based SQD–(Au)MNP molecule, as well as for an epitaxial SQD structure coupled to an Au nanoparticle. It is demonstrated that below a critical value of the interparticle distance the susceptibility of each distinct component of the structure exhibits a characteristic single-resonance spectrum, whereas above this value, the spectrum has three resonances. This phenomenon can be understood in terms of the theory of exciton–plasmon quantum metastates. In addition, the conditions under which optical transparency occurs with a concurrent positive self-phase-modulation coefficient are also identified.

Nonlinear optical rectification of a coupled semiconductor quantum dot – Metallic nanosphere system under a strong electromagnetic field

We present results for the nonlinear optical rectification of an asymmetric GaAs/AlGaAs quantum dot structure coupled to a gold nanosphere under the influence of a strong electromagnetic field. We show that the nonlinear optical rectification coefficient depends strongly on the distance between the quantum dot and the metallic nanosphere and on the direction of the applied electromagnetic field.

Near-infrared light controlling using the photonic crystal with coupled quantum dots in defect layer

We propose a multilayer structure with an active region consisting coupled semiconductor quantum dots to modulate a near-infrared optical probe. The vertically aligned arrays of two quantum dots are simulated to obtain the electron and hole energy eigenvalues. The inter-dot electron and hole tunneling along with coupling laser field are considered to investigate the optical properties of the quantum dot molecules via density matrix method. Probe field transmission through the designed one dimensional photonic crystal, with composed quantum dot molecules defect layer, is monitored. The necessary values of the controlling parameters, i.e. tunneling strength, coupling field intensity and its relative phase with respect to the probe signal for operating in different ON/OFF and amplified-ON regimes are determined. The dynamical response of the quantum dot molecules is also investigated to obtain the switching time between these three regimes. The obtained results confirm that the proposed structure can operate as an optical switch or amplifier in communication technology.

Guest Editorial Mini-Special Issue on International Quantum Cascade Lasers School and Workshop (IQCLSW 2016)

The papers in this special section were presented at the International Quantum Cascade Lasers School and Workshop (IQCLSW 2016). Quantum cascade lasers (QCLs) are unipolar optoelectronic devices that exploit optical transitions between engineered electronic subbands created in multiple coupled semiconductor quantum wells. The large number of nano metre thick semiconductor layers and the complexity of the overall structure, makes the QCL the most impressive demonstration of the capabilities offered by band structure engineering and state-of-the-art materials growth technologies.

Formation of exciton rings and localized bright spots in coupled semiconductor quantum wells

We consider indirect excitons generated at the ring-shaped boundaries between electron- and hole-rich regions in semiconductor quantum wells (QW's). We show theoretically that the in-plane translational motion of the excitons is confined in the radial direction. The confinement potential results from the electrostatic interaction of the exciton dipole moment with the in-plane electric field induced at the boundary by the macroscopic charge separation. Our results directly apply to the external ring and the localized bright spots (LBS) observed in the photoluminescense (PL) pattern of indirect excitons.

Reconstruction of exciton wave functions of coupled quantum emitters including spin with ultrafast spectroscopy using localized nanooptical fields

Coulomb-induced resonance energy transfer mechanisms between coupled nanostructures lead to the formation of new, delocalized exciton states. Their hybrid wave functions can be decomposed into the basis of local states of the uncoupled system by the use of coherent, spatially resolved spectroscopy. The suggested quantum state tomography protocol combines nanooptical fields with a four-wave mixing technique: At least one pulse of the pulse sequence is spatially localized at a specific quantum emitter. It was suggested to use nanoplasmonic structures together with pulse-shaped fields for the localization. In this paper, the method is applied to a system of two coupled semiconductor quantum dots. The basic reconstruction concept first proposed in Richter et al. (Phys Rev B 86:085308, 2012) and Schlosser et al. (New J Phys 15:025004, 2013) is extended to the case of including different spin states of the excitons in the quantum dots. For this purpose, the theoretical scheme has to be modified and the localized fields need the ability to change their polarization. We show that the application of the developed reconstruction scheme to two-dimensional spectra gives full access to the internal structure of the interacting quantum states.

Influence of magnetic quantum confined Stark effect on the spin lifetime of indirect excitons

We report on the unusual and counter-intuitive behaviour of spin lifetime of excitons in coupled semiconductor quantum wells (CQWs) in the presence of in-plane magnetic field. Instead of conventional acceleration of spin relaxation due to the Larmor precession of electron and hole spins we observe a strong increase of the spin relaxation time at low magnetic fields followed by saturation and decrease at higher fields. We argue that this non-monotonic spin relaxation dynamics is a fingerprint of the magnetic quantum confined Stark effect. In the presence of electric field along the CQW growth axis, an applied magnetic field efficiently suppresses the exciton spin coherence, due to inhomogeneous broadening of the $g$-factor distribution.

Optical refrigeration with coupled quantum wells.

Refrigeration of a solid-state system with light has potential applications for cooling small-scale electronics and photonics. We show theoretically that two coupled semiconductor quantum wells are efficient cooling media for optical refrigeration because they support long-lived indirect electron-hole pairs. Thermal excitation of these pairs to distinct higher-energy states with faster radiative recombination allows an efficient escape channel to remove thermal energy from the system. This allows reaching much higher cooling efficiencies than with single quantum wells. From band-diagram calculations along with an experimentally realistic level scheme we calculate the cooling efficiency and cooling yield of different devices with coupled quantum wells embedded in a suspended nanomembrane. The dimension and composition of the quantum wells allow optimizing either of these quantities, which cannot, however, be maximized simultaneously. Quantum-well structures with electrical control allow tunability of carrier lifetimes and energy levels so that the cooling efficiency can be optimized over time as the thermal population decreases due to the cooling.

A tunable bistable device based on a coupled quantum dot–metallic nanoparticle nanosystem

We theoretically propose a scheme of a tunable bistable device based on a coupled semiconductor quantum dot–metal nanoparticle nanosystem in the simultaneous presence of a strong pump laser and a weak probe laser with different frequencies. The results show that it is easy to turn on or off the optical bistable effect in such system by switching the polarization direction of the pump field, and the bistability thresholds are highly sensitive to the intensity, frequency, polarization direction of the pump field, and the interparticle distance. In addition, the nonlinear absorption in the two stable states exhibits a ratio as high as 104 arising from the three-photon effect, which implies that our nanosystem can also be used as an optical memory cell.

Generating and moving Dirac points in a two-dimensional deformed honeycomb lattice arrayed by coupled semiconductor quantum dots

Analysis of the electronic properties of a two-dimensional (2D) deformed honeycomb structure arrayed by semiconductor quantum dots (QDs) is conducted theoretically by using tight-binding method in the present paper. Through the compressive or tensile deformation of the honeycomb lattice, the variation of energy spectrum has been explored. We show that, the massless Dirac fermions are generated in this adjustable system and the positions of the Dirac cones as well as slope of the linear dispersions could be manipulated. Furthermore, a clear linear correspondence between the distance of movement d (the distance from the Dirac points to the Brillouin zone corners) and the tunable bond angle α of the lattice are found in this artificial planar QD structure. These results provide the theoretical basis for manipulating Dirac fermions and should be very helpful for the fabrication and application of high-mobility semiconductor QD devices.

Coherent manipulation of spontaneous emission spectra in coupled semiconductor quantum well structures.

In triple coupled semiconductor quantum well structures (SQWs) interacting with a coherent driving filed, a coherent coupling field and a weak probe field, spontaneous emission spectra are investigated. Our studies show emission spectra can easily be manipulated through changing the intensity of the driving and coupling field, detuning of the driving field. Some interesting physical phenomena such as spectral-line enhancement/suppression, spectral-line narrowing and spontaneous emission quenching may be obtained in our system. The theoretical studies of spontaneous emission spectra in SQWS have potential application in high-precision spectroscopy. Our studies are based on the real physical system [Appl. Phys. Lett.86(20), 201112 (2005)], and this scheme might be realizable with presently available techniques.

Coherent Single-Electron Transfer in Coupled Semiconductor Quantum Dots Driven by a Few-Cycle Pulse

We theoretically study the coherent transport of a single electron between the ground states of a double coupled quantum dot structure. The coherent transport is externally controlled by applying a few-cycle pulse with an adjustable carrier-envelope phase (CEP). By simulating numerically, it is shown that there exhibits a strong dependence of electron transport on the CEP and on the arrival time of few-cycle pulse. We provide a simple analytical description for this phenomenon by approximating the quantum dot structure as a three-level Λ-type system. These results also illustrate the potential of utilizing excitation in coupled quantum dots as a means of measuring the CEP of few-cycle pulses.

Strongly modified four-wave mixing in a coupled semiconductor quantum dot-metal nanoparticle system

We study the four-wave mixing effect in a coupled semiconductor quantum dot-spherical metal nanoparticle structure. Depending on the values of the pump field intensity and frequency, we find that there is a critical distance that changes the form of the spectrum. Above this distance, the four-wave mixing spectrum shows an ordinary three-peaked form and the effect of controlling its magnitude by changing the interparticle distance can be obtained. Below this critical distance, the four-wave mixing spectrum becomes single-peaked; and as the interparticle distance decreases, the spectrum is strongly suppressed. The behavior of the system is explained using the effective Rabi frequency that creates plasmonic metaresonances in the hybrid structure. In addition, the behavior of the effective Rabi frequency is explained via an analytical solution of the density matrix equations.