Matthias-Rene Dachner

Formation dynamics of an entangled photon pair { a temperature dependent analysis

We theoretically study the polarization entanglement of photons generated by the biexciton cascade in a GaAs/InAs semiconductor quantum dot (QD) located in a nanocavity. A detailed analysis of the complex interplay between photon and carrier coherences and phonons which occurs during the cascade allows us to clearly identify the conditions under which entanglement is generated and destroyed. A quantum state tomography is evaluated for varying exciton fine-structure splittings. Also, by constructing an effective multiphonon Hamiltonian which couples the continuum of the QD-embedding wetting layer states to the quantum confined states, we investigate the relaxation of the biexciton and exciton states. This consistently introduces a temperature dependence to the cascade. Considering typical Stranski-Krastanov grown QDs for temperatures around 80 K the degree of entanglement starts to be affected by the dephasing of the exciton states and is ultimately lost above 100 K.

Decay dynamics of excitonic polarons in InAs/GaAs quantum dots

We present time-resolved studies of the exciton-phonon interaction in self-assembled InAs/GaAs quantum dots. Different scattering and luminescence processes were investigated by time-resolved spectroscopy exciting resonantly into the quantum dot’s electronic structure. By studying the characteristic decay times of the ground state and of several phonon-assisted recombinations we were able to distinguish a resonant Raman process from a phonon-assisted photoluminescence process which are always simultaneously present and can interfere with each other. While lifetimes under 30 ps were observed for the coherent Raman process, the incoherent phonon-assisted recombination exhibited typical lifetimes of around 1 ns independently of the excitation energy. We conclude that under resonant excitation the dominant radiative recombination process in this system always involves an electronic state of the ground state of the quantum dot’s electronic structure. Combining temperature-dependent and time-resolved measuremen...

Effective Hamiltonian approach to multiphonon effects in self assembled quantum dots

We present a perturbative approach to multiphonon assisted carrier relaxation and optical dephasing in self assembled quantum dots.

Quantum light emission from cavity enhanced LEDs

We propose further experimental and theoretical investigations of optical devices in the single-photon limit and present a theoretical framework to study parameter dependent quantum light emission in semiconductor environments.

Lasing dynamics of quantum‐dot vertical‐cavity surface‐emitting lasers using microscopically calculated Maxwell‐Bloch equations

We present the lasing dynamics of an electrically pumped quantum dot vertical‐cavity surface‐emitting lasers (QD‐VCSELs) using self‐consistently combined QD‐WL Maxwell‐Bloch equations. In order to determine the dephasing times of the system, Coulomb and electron‐phonon scattering processes between the quantum dot (QD) states and the QD‐embedding wetting layer (WL) states are microscopically calculated and implemented into the material equations. The QD‐WL Maxwell‐Bloch equations are used to study the characteristics of the switch‐on dynamics which are crucial for high‐speed optical systems. The carrier dynamics and the electric field propagation are evaluated using the finite‐difference time‐domain (FDTD) method within the full structure of QD‐VCSELs.

Theory of few photon dynamics in electrically pumped light emitting quantum dot devices

Quantum dot based light emitters can be used as sources of nonclassical light. We focus on the theory of InAs/GaAs quantum dots embedded in a two dimensional wetting layer at low electrical pump currents but strongly correlated electron-photon dynamics. For this purpose a self-consistent theory of transport and emission is developed. A substantial carrier heating in such devices is predicted and the relation of electrical pumping and single photon emission is analyzed within the photon-probability-cluster-expansion.

Phonon interaction on a single quantum dot emission line

We studied the coupling between the lattice vibrations and the electronic states of a single electrically pumped InAs/GaAs quantum dot. The experimental observed spectra agree excellent with theoretical modeling considering real QD structural parameters.

Theory of electron dynamics in light emitting quantum dot devices

Quantum dot based light emitters can be used as laser and single photon devices[1]. In particular, we focus on the theory of InAs/GaAs quantum dots (QDs) embedded in a two dimensional wetting layer (WL). For simulating real devices, the interactions between electrons and holes confined in the QDs and the wetting layer are important. Therefore, we include Coulomb interaction as well as electron-phonon coupling, considering multi-phonon processes based on an effective multiphonon Hamilton operator. Within this theoretical approach, the investigation in temporal domain is carried out for two limits: