Quantum Dot Microcavity System Research Articles

Effect of the Förster interaction and the pulsed pumping on the quantum correlations of a two quantum dot-microcavity system in the strong coupling regime

The quantum correlations of a system of two quantum dots with Föster interaction (Γ) in a microcavity with strongly coupled dissipation and a single mode of the electromagnetic field and driven by a laser pulse were studied theoretically, using the formalism of the master equation in Lindbland form. The energy eigenvalues of the system were studied as a function of detuning for the first and second excitation varieties. Concurrence (C), formation entanglement (EoF), mutual information (I) and quantum discord (Q) are studied as a function of time considering different values of Föster coupling, varying the pump times of the simulated laser pulse and pulse intensity. We found a discrepancy between EoF and C as entanglement quantifiers, noting that concurrence reaches much higher values than EoF; so concurrence can indicate results that are well above the EoF. The presence of the Föster interaction favors that the quantum discord is the dominant correlation in the system, which indicates that the system maintains quantum correlations even when the entanglement of the system has disappeared, but that it is affected by the increase in the laser pump time.

Weak to strong coupling conditions for a microcavity–quantum dot system under incoherent pumping

We theoretically study the power spectra of a microcavity–quantum dot system under incoherent pumping of photons and excitons, considering two models: one with linked cavity loss rate and pumping, and one with independent cavity loss rate and pumping. We investigate the transition from strong to weak coupling under low and high incoherent pumping in each model and determine sets of parameters necessary to achieve these regimes of light–matter interaction. Despite their differences, both models exhibit a sequence of transitions between weak, strong, and weak coupling as the pumping is increased. This prediction has not yet been observed.

Resonant Two-Laser Spin-State Spectroscopy of a Negatively Charged Quantum-Dot–Microcavity System with a Cold Permanent Magnet

Resonant Two-Laser Spin-State Spectroscopy of a Negatively Charged Quantum-Dot–Microcavity System with a Cold Permanent Magnet

Four-wave mixing dynamics of a strongly coupled quantum-dot–microcavity system driven by up to 20 photons

The Jaynes-Cummings (JC) model represents one of the simplest ways in which single qubits can interact with single photon modes, leading to profound quantum phenomena like superpositions of light and matter states. One system, that can be described with the JC model, is a single quantum dot embedded in a micropillar cavity. In this joint experimental and theoretical study we investigate such a system using four-wave mixing (FWM) micro-spectroscopy. Special emphasis is laid on the dependence of the FWM signals on the number of photons injected into the microcavity. By comparing simulation and experiment, which are in excellent agreement with each other, we infer that up to ~20 photons take part in the observed FWM dynamics. Thus we verify the validity of the JC model for the system under consideration in this non-trivial regime. We find that the inevitable coupling between the quantum dot exciton and longitudinal acoustic phonons of the host lattice influences the real time FWM dynamics and has to be taken into account for a sufficient description of the quantum dot-microcavity system. Performing additional simulations in an idealized dissipation-less regime, we observe that the FWM signal exhibits quasi-periodic dynamics, analog to the collapse and revival phenomenon of the JC model. In these simulations we also see that the FWM spectrum has a triplet structure, if a large number of photons is injected into the cavity.

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.

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.

DYNAMICS AND ENTANGLEMENT OF A QUANTUM DOT-CAVITY SYSTEM COUPLED BY A NON-LINEAR OPTICAL INTERACTION

Se propone un modelo teórico sencillo para un sistema disipativo de punto cuántico-microcavidad que interactúan a través de una interacción óptica no lineal. El formalismo de la ecuación maestra en la forma de Lindblad es considerado para estudiar la dinámica del sistema en los regímenes de acoplamiento débil y fuerte, respectivamente. El espectro de fotoluminiscencia del sistema en el límite estacionario es calculado en forma exacta, y se muestra el efecto de la interacción óptica no lineal explícitamente sobre éste. Se calcula el entrelazamiento del sistema, y se encuentra resurgimientos y muerte s\'ubita del entrelazamiento. Adicionalmente, se estudia la relación entre los términos de interacción luz-materia (Jaynes-Cummings) e interacción óptica no lineal (medio Kerr) por medio del número medio de fotones.

Transition from Jaynes-Cummings to Autler-Townes ladder in a quantum dot–microcavity system

We study experimentally and theoretically a coherently-driven strongly-coupled quantum dot-microcavity system. Our focus is on physics of the unexplored intermediate excitation regime where the resonant laser field dresses a strongly-coupled single exciton-photon (polariton) system resulting in a ladder of laser-dressed Jaynes-Cummings states. In that case both the coupling of the emitter to the confined light field of the microcavity and to the light field of the external laser are equally important, as proved by observation of injection pulling of the polariton branches by an external laser. This intermediate interaction regime is of particular interest since it connects the purely quantum mechanical Jaynes-Cummings ladder and the semi-classical Autler-Townes ladder. Exploring the driving strength-dependence of the mutually coupled system we establish the maximum in the resonance fluorescence signal to be a robust fingerprint of the intermediate regime and observe signatures indicating the laser-dressed Jaynes-Cummings ladder. In order to address the underlying physics we excite the coupled system via the matter component of fermionic nature undergoing saturation - in contrast to commonly used cavity-mediated excitation.

All-optical tailoring of single-photon spectra in a quantum-dot microcavity system

Semiconductor quantum-dot cavity systems are promising sources for solid-state based on-demand generation of single photons for quantum communication. Commonly, the spectral characteristics of the emitted single photon are fixed by system properties such as electronic transition energies and spectral properties of the cavity. In the present work we study single-photon generation from the quantum-dot biexciton through a partly stimulated non-degenerate two-photon emission. We show that frequency and linewidth of the single photon can be fully controlled by the stimulating laser pulse, ultimately allowing for efficient all-optical spectral shaping of the single photon.

纯消相干对量子点-微腔激射性质的影响

纯消相干对量子点-微腔激射性质的影响

Optical nonlinearity in a quantum dot–microcavity system under an external magnetic field

We theoretically study the dynamics of a strongly coupled quantum dot–bimodal microcavity system under an external magnetic field, where the nondegenerate excitonic spin states caused by the Zeeman effect are coupled to both orthogonal cavity modes. We develop an effective cavity quantum electrodynamics model, demonstrate the polarization-related nonlinear response under a linearly polarized pulse excitation by calculating the time-resolved intracavity photon number, and investigate the dependence of system parameters on the nonlinearity. In addition, we show that, when driven by two pulses with perpendicular polarization and a relative time delay, the coupled system suppresses the delayed one, which can be applied to polarized optical switching at a single-photon level.

Photoluminescence of a microcavity quantum dot system in the quantum strong-coupling regime

The Jaynes-Cummings model, describing the interaction between a single two-level system and a photonic mode, has been used to describe a large variety of systems, ranging from cavity quantum electrodynamics, trapped ions, to superconducting qubits coupled to resonators. Recently there has been renewed interest in studying the quantum strong-coupling (QSC) regime, where states with photon number greater than one are excited. This regime has been recently achieved in semiconductor nanostructures, where a quantum dot is trapped in a planar microcavity. Here we study the quantum strong-coupling regime by calculating its photoluminescence (PL) properties under a pulsed excitation. We discuss the changes in the PL as the QSC regime is reached, which transitions between a peak around the cavity resonance to a doublet. We particularly examine the variations of the PL in the time domain, under regimes of short and long pulse times relative to the microcavity decay time.

Photon emission from a quantum dot-photonic crystal microcavity system: The role of pumping and cavity decay rates

We present a study of photon emission from a photonic crystal microcavity-quantum dot system. We take into account dissipative and pumping mechanisms consisting of the decay rate of cavity photons with the pumping rates of exciton and cavity. Numerically, we calculate the exciton state in a model quantum dot through the variational approach and photonic crystal microcavity L1 and modified-L1 modes through the GME (guided mode expansion) code, respectively. Second order correlation function of cavity (g(2)(τ)) and populations of photons and exciton have been obtained by using master equation and quantum regression theorem. Detailed investigation of the effect of pumping rates and cavity decay rate on the populations and g(2)(0) has been done in the steady state regime. Results demonstrate that when modified-L1 microcavity and exciton modes are off-resonance, detuning has opposite surprising effects on antibunching effect at different values of pumping rates.

On‐Chip Quantum Optics with Quantum Dot Microcavities

A novel concept for on-chip quantum optics using an internal electrically pumped microlaser is presented. The microlaser resonantly excites a quantum dot microcavity system operating in the weak coupling regime of cavity quantum electrodynamics. This work presents the first on-chip application of quantum dot microlasers, and also opens up new avenues for the integration of individual microcavity structures into larger photonic networks.

Spin-Resolved Purcell Effect in a Quantum Dot Microcavity System

We demonstrate the spin selective coupling of the exciton state with cavity mode in a single quantum dot (QD)-micropillar cavity system. By tuning an external magnetic field, each spin polarized exciton state can be selectively coupled with the cavity mode due to the Zeeman effect. A significant enhancement of spontaneous emission rate of each spin state is achieved, giving rise to a tunable circular polarization degree from -90% to 93%. A four-level rate equation model is developed, and it agrees well with our experimental data. In addition, the coupling between photon mode and each exciton spin state is also achieved by varying temperature, demonstrating the full manipulation over the spin states in the QD-cavity system. Our results pave the way for the realization of future quantum light sources and the quantum information processing applications.

Time-resolved luminescence of the coupled quantum dot–microcavity system: general theory

The general theory of the time-resolved luminescence of the coupled system consisting of a single-mode microcavity and a two-level quantum dot containing one electron placed inside this microcavity is presented. It is based on the study of the time evolution of the density matrix of a larger system consisting of one electron in the two-level quantum dot, single-mode photons in the microcavity and external photons in a spatial region in which the emitted photons are detected. The decoherence of the system is taken into account in the Markov approximation. The explicit analytical form of the time dependence of the intensity of the emitted photon beam is established. It depends not only on the physical parameters of the system but also contains the matrix elements determining the initial condition of the luminescence process.

Exciton spin state mediated photon-photon coupling in a strongly coupled quantum dot microcavity system

Semiconductor microcavities play a key role in connecting exciton states and photons in advancing quantum information in solids. In this work we report on coherent interaction between high quality microcavity photon modes and spin states of a quantum dot in the strong coupling regime of cavity quantum electrodynamics. The coupling between the photon and exciton modes is studied by varying the temperature, where the spin states are resolved with a magnetic field applied in Faraday configuration. A detailed oscillator model is used to extract coupling parameters of the individual spin and cavity modes, which shows that the coupling depends on features of the mode symmetries. Our results demonstrate an effective coupling between photon modes that is mediated by the exciton spin states.

Effective cavity pumping from weakly coupled quantum dots

We derive the effective cavity pumping and decay rates for the master equation of a quantum dot–microcavity system in the presence of N weakly coupled dots. We show that the in-flow of photons is not linked to the out-flow by thermal equilibrium relationships.

Characterization of dynamical regimes and entanglement sudden death in a microcavityquantum dot system

The relation between the dynamical regimes (weak and strong coupling) and entanglementfor a dissipative quantum dot microcavity system is studied. In the framework of aphenomenological temperature model an analysis in both temporal (populationdynamics) and frequency domain (photoluminescence) is carried out in order toidentify the associated dynamical behavior. The Wigner function and concurrenceare employed to quantify the entanglement in each regime. We find that suddendeath of entanglement is a typical characteristic of the strong coupling regime.

Density matrix of strongly coupled quantum dot – microcavity system

Any two-level quantum system can be used as a quantum bit (qubit)-the basic element of all devices and systems for quantum information and quantum computation. Recently it was proposed to study the strongly coupled system consisting of a two-level quantum dot and a monoenergetic photon gas in a microcavity-the strongly coupled quantum dot-microcavity (QD-MC) system for short, with the Jaynes-Cumming total Hamiltonian, for the application in the quantum information processing. Different approximations were applied in the theoretical study of this system. In this work, on the basis of the exact solution of the Schrodinger equation for this system without dissipation we derive the exact formulae for its density matrix. The realization of a qubit in this system is discussed. The solution of the system of rate equation for the strongly coupled QD-MC system in the presence of the interaction with the environment was also established in the first order approximation with respect to this interaction.