It is shown that the ordinary semiclassical theory of the absorption of light by exciton states is not completely satisfactory (in contrast to the case of absorption due to interband transitions). A more complete theory is developed. It is shown that excitons are approximate bosons, and, in interaction with the electromagnetic field, the exciton field plays the role of the classical polarization field. The eigenstates of the system of crystal and radiation field are mixtures of photons and excitons. The ordinary one-quantum optical lifetime of an excitation is infinite. Absorption occurs only when "three-body" processes are introduced. The theory includes "local field" effects, leading to the Lorentz local field correction when it is applicable. A Smakula equation for the oscillator strength in terms of the integrated absorption constant is derived.

a Quantum-Mechanical Theory of the Contribution of Excitons to the Complex Dielectric Constant of Crystals.

Polarization-entangled photon pairs are generated from an In(Ga)As quantum dot by setting the pump intensity such that the inversion of the quantum dot from the ground to the biexcitonic state is the most probable transition. On-demand generation is demonstrated with an ultrahigh purity, a high entanglement fidelity and high two-photon-interference non-post-selective visibilities.

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On-demand generation of indistinguishable polarization-entangled photon pairs

We show that resonance fluorescence, i.e., the resonant emission of a coherently driven two-level system, can be realized with a semiconductor quantum dot. The dot is embedded in a planar optical microcavity and excited in a waveguide mode so as to discriminate its emission from residual laser scattering. The transition from the weak to the strong excitation regime is characterized by the emergence of oscillations in the first-order correlation function of the fluorescence, $g(\ensuremath{\tau})$, as measured by interferometry. The measurements correspond to a Mollow triplet with a Rabi splitting of up to $13.3\text{ }\text{ }\ensuremath{\mu}\mathrm{eV}$. Second-order correlation measurements further confirm nonclassical light emission.

Resonance fluorescence from a coherently driven semiconductor quantum dot in a cavity.

Electron-phonon interaction is a major source of optical dephasing in semiconductor quantum dots. Within a density matrix theory the electron-phonon interaction is considered up to the second order of a correlation expansion, allowing the calculation of the quantum kinetic dephasing dynamics of optically induced nonlinearities in GaAs quantum dots for arbitrary pulse strengths and shapes. We find Rabi oscillations renormalized and a damping that depends on the input pulse strength, a behavior not known from exponential dephasing mechanisms.

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Phonon-assisted damping of Rabi oscillations in semiconductor quantum dots.

Semiconducting transition metal dichalcogenide (TMDC) monolayers have exceptional physical properties They show bright photoluminescence due to their unique band structure and absorb more than 10% of the light at their excitonic resonances despite their atomic thickness At room temperature, the width of the exciton transitions is governed by the exciton–phonon interaction leading to strongly asymmetric line shapes TMDC monolayers are also extremely flexible, sustaining mechanical strain of about 10% without breaking The excitonic properties strongly depend on strain For example, exciton energies of TMDC monolayers significantly redshift under uniaxial tensile strain Here, we demonstrate that the width and the asymmetric line shape of excitonic resonances in TMDC monolayers can be controlled with applied strain We measure photoluminescence and absorption spectra of the A exciton in monolayer MoSe2, WSe2, WS2, and MoS2 under uniaxial tensile strain We find that the A exciton substantially narrows an

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Strain control of exciton-phonon coupling in atomically thin semiconductors

We investigate the optical properties of a Coulomb-coupled double-quantum dot system excited by coherent light pulses. Basic effects of Coulomb coupling regarding linear and nonlinear optical processes are discussed. By numerically solving the Heisenberg equation of motion we are able to present the temporal evolution of the system’s density matrix for a wide range of coupling parameters. The two main coupling effects in dipole approximation, biexcitonic shift and Forster energy transfer, are investigated and their qualitative and quantitative influence on absorption spectra, Rabi oscillations, and single- and two-pulse excitation is discussed. We present simulated differential transmission spectra to allow for comparison with recent experimental studies.

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Theory of ultrafast nonlinear optics of Coulomb-coupled semiconductor quantum dots: Rabi oscillations and pump-probe spectra

The phonon-induced dephasing dynamics of semiconductor quantum dots during nonlinear optical excitation is studied using quantum kinetic equations We find that despite the decoherence process Rabi oscillations occur even for relatively long pulse durations and that their signatures in pump-probe experiments only get suppressed for high input pulse areas

Phonon-induced damping of Rabi oscillations in semiconductor quantum dots

The occurrence of non-Lorentzian lineshapes is analyzed for a variety of nanooptical semiconductor
systems such as quantum wells and quantum dots. Their origin is traced back to light–matter
interaction (light propagation) and many-particle correlations (electron–electron and electron–
phonon interaction).

Light Propagation- and Many-particle-induced Non-Lorentzian Lineshapes in Semiconductor Nanooptics

A non-Markovian quantum kinetic theory of the coupled electron-phonon system in semiconductor quantum dots is used to analyze the nonlinear dipole decoherence and light propagation dynamics for arbitrary pulse strengths and lengths.

J. Danckwerts

Papers

Phonon-assisted damping of Rabi oscillations in semiconductor quantum dots.

Theory of ultrafast nonlinear optics of Coulomb-coupled semiconductor quantum dots: Rabi oscillations and pump-probe spectra

Phonon-induced damping of Rabi oscillations in semiconductor quantum dots

Light Propagation- and Many-particle-induced Non-Lorentzian Lineshapes in Semiconductor Nanooptics

Damping of electron density Rabi-oscillations and self-induced-transparency in semiconductor quantum dots