Quantum Dot-cavity Research Articles

Purcell-Enhanced Single Photon Source Based on a Deterministically Placed WSe2 Monolayer Quantum Dot in a Circular Bragg Grating Cavity.

We demonstrate a deterministic Purcell-enhanced single photon source realized by integrating an atomically thin WSe2 layer with a circular Bragg grating cavity. The cavity significantly enhances the photoluminescence from the atomically thin layer and supports single photon generation with g(2)(0) < 0.25. We observe a consistent increase of the spontaneous emission rate for WSe2 emitters located in the center of the Bragg grating cavity. These WSe2 emitters are self-aligned and deterministically coupled to such a broadband cavity, configuring a new generation of deterministic single photon sources, characterized by their simple and low-cost production and intrinsic scalability.

Light transmission from a strongly coupled QD-Cavity system driven by a laser pulse

Abstract Cavity transmission and second-order coherence function of a quantum dot-cavity system strongly coupled and driven by a laser pulse were studied theoretically. The calculations were carried out by solving the master equation in the Lindblad form. A quantum dot (QD) modeled as a two-level system is assumed to interact with a single-mode quantized electromagnetic field following the Jaynes-Cummings model. Furthermore, a classic pulse with a time-varying profile is considered to interact with the cavity mode. Lindbladian includes spontaneous emission losses, cavity decay and, pure QD dephasing. Cavity transmission and second-order coherence were studied as functions of time considering various pulse shapes and different values of full width at half maximum (FWHM), pulse intensity, and pure QD dephasing. We found that the cavity transmission shows an oscillatory behavior, which is a sign of strong coupling in the system. The pulses considered have similar effects on the cavity transmission. According to the values obtained for the second-order coherence function, the QD-cavity system strongly coupled and excited with classical light works as a quantum light source that exhibits sub-Poissonian statistics and photon bunching phenomenon for all pulses.

Controllable four-wave mixing based on quantum dot-cavity coupling system

We theoretically study the four-wave mixing (FWM) response in a quantum dot-cavity coupling system, where a two-level quantum dot (QD) is placed in an optical cavity while the cavity mode is coupled to the nanomechanical resonator via radiation pressure. The influences of the QD-cavity coupling strength, the Rabi coupling strength of the QD, and the power of the pump light on the FWM intensity are mainly considered. The numerical results show that the FWM intensity in this hybrid system can be significantly enhanced by increasing the QD-cavity coupling strength. In addition, the FWM intensity can be effectively modulated by the Rabi coupling strength and the pump power. Furthermore, the effects of the cavity decay rate and the cavity-pump detuning on the FWM signal are also explored. The obtained results may have potential applications in the fields of quantum optics and quantum information science.

Formation of spectral triplets induced by parity deformation in a quantum dot–cavity system

In this work, we conduct an investigation on the optical emission properties of a pumped-dissipative QD–cavity system within the Lindblad master equation approach, where the cavity mode is modeled through the R-deformed realization of the Heisenberg algebra (RDHA). We found that the parity deformation parameter associated with the RDHA gives rise to a collective effect in the photonic emission of the system by reordering of the one-photon optical transitions, and it is demonstrated that there are two critical values for this parameter where a new type of spectral triplet arises in the emission spectrum. Our results reveal that depending on the critical value of the deformation parameter, the spectral triplets observed in the emission spectrum exhibit signatures of the weak- and strong-coupling regimes simultaneously.

Stability Analysis and Bifurcation in External Cavity Quantum Dot Semiconductor Laser

A simplified mathematical model to describe the nonlinear dynamics of a quantum dot laser (QDLs) coupled with external cavity was modified. This system is currently modeled by very complex equations which are intractable analytically and numerically. The model derived is simple, and efficient to provide full insight of the dynamics of the QDLs while compared with the well-known classical models. The equilibrium points and stability analysis of critical points is carried out. Various bifurcation scenarios are obtained numerically showing several striking routes to chaos.

On-demand generation of higher-order Fock states in quantum-dot–cavity systems

The on-demand preparation of higher-order Fock states is of fundamental importance in quantum information sciences. We propose and compare different protocols to generate higher-order Fock states in solid state quantum-dot--cavity systems. The protocols make use of a series of laser pulses to excite the quantum dot exciton and off-resonant pulses to control the detuning between dot and cavity. Our theoretical studies include dot and cavity loss processes as well as the pure-dephasing type coupling to longitudinal acoustic phonons in a numerically complete fashion. By going beyond the two-level approximation for quantum dots, we study the impact of a finite exchange splitting, the impact of a higher energetic exciton state, and an excitation with linearly polarized laser pulses leading to detrimental occupations of the biexciton state. We predict that under realistic conditions, a protocol which keeps the cavity at resonance with the quantum dot until the desired target state is reached is able to deliver fidelities to the Fock state $| 5\rangle$ well above $40\,\%$.

Controllable bistable optical switch and normal mode splitting in hybrid optomechanical semiconductor microcavity containing single quantum dot driven by amplitude modulated field

We theoretically explore optical bistability for the possible signature of all-optical switching and their performance in a hybrid quantum optomechanical system comprising of two semiconductor microcavities coupled optically. One of the cavity is driven by an external amplitude-modulated pump laser while the second cavity, which contains a quantum dot (QD), is indirectly driven by light transmitted from the first cavity and a transverse optical field. The generated bistable behavior due to optomechanical nonlinearity shows a typical optical switching behavior and it can be controlled by changing the laser power, QD cavity coupling, modulating amplitude/frequency and the optomechanical coupling. A clear signature of energy exchange between the mechanical and optical modes is visible from the mechanical displacement spectrum. These results suggest that the present system can be used in sensitive optical switches and optical sensors.

Semiclassical modeling of coupled quantum-dot–cavity systems: From polaritonlike dynamics to Rabi oscillations

Semiconductor quantum dots in photonic cavities are strongly coupled light-matter systems with prospective applications in optoelectronic devices and quantum information processing. Here we present a theoretical study of the coupled exciton--light field dynamics of a planar quantum dot ensemble, treated as two-level systems, embedded in a photonic cavity modeled by Maxwell's equations. When excited by coupling an external short laser pulse into the cavity, we find an exciton-polariton-like behavior for weak excitation and Rabi oscillations for strong excitation with a sharp transition between these regimes. In the transition region we find highly non-linear dynamics involving high harmonics of the fundamental oscillation. We perform a numerical study based on the Finite-Difference-Time-Domain method for the solution of Maxwell's equations coupled to Bloch equations for the quantum dots and also derive an analytical model to describe the coupled cavity-quantum dot system, which allows us to describe the light field dynamics in terms of a Newton-like dynamics in an effective anharmonic potential. From the shape of this potential combined with the initial conditions the transition can be well understood. The model is then extended to a broadened ensemble of quantum dots. For weak excitation the polariton spectrum broadens and the lines slightly shift, however, the sharp transition to the Rabi oscillation regime is still present. Furthermore, we find a second, lower threshold with additional lines in the spectra which can be traced back to Rabi oscillations driven by the polariton modes. Our approach provides new insights in the dynamics of both quantum dot and light field in the photonic structure.

Transiently changing shape of the photon number distribution in a quantum-dot–cavity system driven by chirped laser pulses

We have simulated the time evolution of the photon number distribution in a semiconductor quantum dot-microcavity system driven by chirped laser pulses and compare with unchirped results. When phonon interactions with the dot are disregarded - thus corresponding to the limit of atomic cavity systems - chirped pulses generate photon number distributions that change their shape drastically in the course of time. Phonons have a strong and qualitative impact on the photon statistics. The asymmetry between phonon absorption and emission destroys the symmetry of the photon distributions obtained for positive and negative chirps. While for negative chirps transient distributions resembling thermal ones are observed, for positive chirps the photon number distribution still resembles its phonon-free counterpart but with overall smoother shapes. In sharp contrast, using unchirped pulses of the same pulse area and duration wave-packets are found that move up and down the Jaynes-Cummings ladder with a bell-shape that changes little in time. For shorter pulses and lower driving strength Rabi-like oscillations occur between low photon number states. For all considered excitation conditions transitions between sub- and super-Poissonian statistics are found at certain times. For resonant driving with low intensity the Mandel parameter oscillates and is mostly negative, which indicates a non-classical state in the cavity field. Finally, we show that it is possible that the Mandel parameter dynamically approaches zero and still the photon distribution exhibits two maxima and thus is far from being a Poissonian.

Magnetic and temperature control in the emission of a quantum dot strongly coupled to a microcavity

In this paper, we use a theoretical model in order to describe a quantum dot-cavity system at finite temperature. In addition, a tilted magnetic field is included which generates two bright exciton states with definite polarization that can be tuned by the Zeeman and diamagnetic shift. Strong coupling between the cavity and two bright states is observed when the magnetic field varies in strength and direction. Further, the magnetic field provides an additional parameter which allows the control in the emission of photons with right polarization when the system is pumped with photons of left polarization.

Extended polarized semiclassical model for quantum-dot cavity QED and its application to single-photon sources

We present a simple extension of the semi-classical model for a two-level system in a cavity, in order to incorporate multiple polarized transitions, such as those appearing in neutral and charged quantum dots (QDs), and two nondegenerate linearly polarized cavity modes. We verify the model by exact quantum master equation calculations, and experimentally using a neutral QD in a polarization non-degenerate micro-cavity, in both cases we observe excellent agreement. Finally, the usefulness of this approach is demonstrated by optimizing a single-photon source based on polarization postselection, where we find an increase in the brightness for optimal polarization conditions as predicted by the model.

Generation of large-scale W states in a cavity–quantum dot system

We present a scheme for generating large-scale W states based on an expansion mechanism in a cavity–quantum dot system. In cases in which the number of particles is even (2n), the probability of success will be 1.0. In cases in which the number is odd (2n − 1), the probability of success will be 1 − 1/2n. As the number of particles increases, the probability of success is closer to 1. Meanwhile, the fidelity of the obtained state decreases slowly as the number of particles increases. Numerical simulation and discussions show that the scheme can be implemented in the current experimental technology.

Surface-passivated high-Q GaAs photonic crystal nanocavity with quantum dots

Photonic crystal (PhC) nanocavities with high quality (Q) factors have attracted much attention because of their strong spatial and temporal light confinement capability. The resulting enhanced light–matter interactions are beneficial for diverse photonic applications, ranging from on-chip optical communications to sensing. However, currently achievable Q factors for active PhC nanocavities, which embed active emitters inside, are much lower than those of the passive structures because of large optical loss, presumably originating from light scattering by structural imperfections and/or optical absorptions. Here, we demonstrate a significant improvement of Q factors up to ∼160 000 in GaAs active PhC nanocavities using a sulfur-based surface passivation technique. This value is the highest ever reported for any active PhC nanocavities with semiconductor quantum dots. The surface-passivated cavities also exhibit reduced variation in both Q factors and cavity resonant wavelengths. We find that the improvement in the cavity performance presumably arises from suppressed light absorption at the surface of the PhC’s host material by performing a set of PL measurements in spectral and time domains. With the surface passivation technique, we also demonstrate a strongly coupled single quantum dot-cavity system based on a PhC nanocavity with a high Q factor of ∼100 000. These results will pave the way for advanced quantum dot-based cavity quantum electrodynamics and GaAs micro/nanophotonic applications containing active emitters.

Deterministic single-photon subtraction based on a coupled single quantum dot-cavity system.

We present a scheme for realizing deterministic single-photon subtraction in a coupled single quantum dot-cavity solid-state system. The device consists of a charged quantum dot and its coupled bimodal photonic crystal cavity with a moderate magnetic field applied in a Voigt configuration. We numerically simulate injection of optical pulses into one of the cavity modes and show that the system deterministically transfers one photon into the second cavity mode for input pulses in the form of both Fock states and coherent states. This device has potential in the application of a compact and integrated solid-state based device for quantum information processing.

Magnetically controllable photon blockade under a weak quantum-dot–cavity coupling condition

Quantum control of photons has become an area of great interest in the development of quantum technology. Here we explore how an external magnetic field can be exploited to control the statistical properties of photons in a bimodal cavity quantum electrodynamics (CQED) system. Our CQED system is composed of a bimodal micropillar Fabry-P\'erot cavity containing a single $V$-level quantum dot (QD) involving fine-structure-splitting neutral exciton transitions under the effect of the applied magnetic field in the presence of an incident pump laser field driving one cavity mode. With the introduction of the external magnetic field, not only is the conversion of polarization characteristics of photons achieved, but the statistics properties of photons are well engineered and the switching between photon bunching and antibunching is realized in the weak-coupling regime of CQED. The superiority of our system is manifested in the following aspects. (i) Using experimental parameters, we can manipulate the statistical properties of photons by appropriately tuning the strength of the magnetic field under the weak-coupling CQED condition, accompanied by either enhanced antibunching or a transition from antibunching to strong bunching of the light and vice versa. So we can arrive at selective photon statistics. (ii) The strong photon antibunching effect, under nonresonant scenarios but without the need to match the resonant or near-resonant conditions for the cavity and QD, can appear. Furthermore, we find that the multifrequency photon blockade can be generated in the present system, which is different from previous studies about photon blockade only for specific optical detuning. (iii) The high photon occupations or transmissions, simultaneously accompanied by strong photon antibunching in the system, are beneficial to the correlation measurement in practical experiments. This process works with a high quality of photon antibunching and bunching over a wide range of parameters and has potential applications in on-chip quantum information processing. It is hoped that the proposed scheme provides a possibility for the generation of tunable single-photon sources or controllable photon quantum gates.

Quantum correlations from advantageous quasiparticle pictures in a Cavity-QDots System

In this work, we present a quasiparticle strategy to study the Hamiltonian description of the stationary states for two quantum dots–cavity system. We consider three different effective schemes of quasiparticles that give an in-depth insight into the physics involved in the Hamiltonian eigenstates for parameters that optimise or minimise the energy gap condition. We analyse features of quantum measures like fractional composition, linear entropy, and concurrence to observe which one description gives the more complete physical information. Our findings show that a polaritonic-light-matter quasiparticle-approach catches better the physics contained in the whole regimes considered.

Bright and highly-polarized single-photon sources in visible based on droplet-epitaxial GaAs quantum dots in photonic crystal cavities

Solid-state single-photon sources with high purity, high brightness and a large degree of linear polarization are appealing to photonic quantum technologies. However, high-performance single-photon sources based on InAs/GaAs quantum dots (QDs) so far are operating at near infrared range, which limits the detection efficiency and potential compatibility with atomic quantum memory in visible. Here, we explore GaAs droplet epitaxial QDs emitting in visible to achieve bright, pure and highly-polarized single-photon emission via coupling to photonic crystal cavities.

Pure dephasing vs. Phonon mediated off-resonant coupling in a quantum-dot-cavity system

Pure dephasing is widely used in the literature to explain experimental observations on quantum dots in cavities. In many cases, its use is not enough and extra terms need to be “fictitiously” added to accomplish with the observed data as it is the case of cavity pumping of an unknown source. Here we controvert the validity of the pure dephasing mechanism as a source of decoherence and present a theoretical study based on the phonon-mediated coupling that can explain the emission spectrum and photon auto- and cross-correlation results in recent experiments without the need of any artificial assumptions. We also demonstrated that the phonon-mediated coupling accounts for unexplained features recently reported in measurements of photon auto- and cross-correlation functions. Our work illuminates many of the debates in this field and opens up new possibilities for experimental verification and theoretical predictions.

Phonon-induced dephasing in quantum-dot–cavity QED

We present a semi-analytic and asymptotically exact solution to the problem of phonon-induced decoherence in a quantum dot-microcavity system. Particular emphasis is placed on the linear polarization and optical absorption, but the approach presented herein may be straightforwardly adapted to address any elements of the exciton-cavity density matrix. At its core, the approach combines Trotter's decomposition theorem with the linked cluster expansion. The effects of the exciton-cavity and exciton-phonon couplings are taken into account on equal footing, thereby providing access to regimes of comparable polaron and polariton timescales. We show that the optical decoherence is realized by real phonon-assisted transitions between different polariton states of the quantum dot-cavity system, and that the polariton line broadening is well-described by Fermi's golden rule in the polariton frame. We also provide purely analytic approximations which accurately describe the system dynamics in the limit of longer polariton timescales.

Phonon-Induced Enhancement of Photon Entanglement in Quantum Dot-Cavity Systems

We report on simulations of the degree of polarization entanglement of photon pairs simultaneously emitted from a quantum dot-cavity system that demand revisiting the role of phonons. Since coherence is a fundamental precondition for entanglement and phonons are known to be a major source of decoherence, it seems unavoidable that phonons can only degrade entanglement. In contrast, we demonstrate that phonons can cause a degree of entanglement that even surpasses the corresponding value for the phonon-free case. In particular, we consider the situation of comparatively small biexciton binding energies and either finite exciton or cavity mode splitting. In both cases, combinations of the splitting and the dot-cavity coupling strength are found where the entanglement exhibits a nonmonotonic temperature dependence which enables entanglement above the phonon-free level in a finite parameter range. This unusual behavior can be explained by phonon-induced renormalizations of the dot-cavity coupling g in combination with a nonmonotonic dependence of the entanglement on g that is present already without phonons.