Coherent Optical Phenomena in Quantum Dots

Victor Bondarenko, Yang Zhao

Noriaki Tsurumachi, Kazuhiro Komori, Toshiaki Hattori

Ataç İmamoğlu

Semiconductor quantum dots have emerged as promising candidates for studying quantum optical phenomena. Observation of photon antibunching and spontaneous emission limited coherence decay rates have demonstrated that quantum dots behave as artificial atoms. Cavity-quantum electrodynamics (QED) phenomena can be investigated using a single quantum dot embedded inside a photonic nanostructure, where both carriers and photons are confined within sub-micron length scales in all three dimensions. Since quantum dot location inside the cavity is fixed by the growth, this system is free of the stringent trapping requirements that limit its atomic counterpart. Possibility of fabricating photonic nanostructures with ultra-small optical-mode volumes and long photon lifetimes enhances the prospects for applications in quantum information processing. 1

Gang Chen

Stefan Maximilian Strauß

Excitons in quantum dots represent a remarkably good two-level system with a large optical dipole transition moment. Although most research currently focuses on enhancing their already outstanding properties as single photon emitters they become also increasingly interesting for experimental fundamental research due to their large dipole transition moment. This thesis presents studies which explore fundamental phenomena in quantum dots using coherent spectrocopy methods. First, we will first examine the optical properties of site-controlled quantum dots which were grown using a buried stressor via resonance fluorescence. Subsequently, we will show results that were obtained using photocurrent spectroscopy to study single quantum dots that are embedded in micropillar resonators. This is followed by a study of the Wigner time delay induced by a single quantum dot and which shows that the maximum delay is larger than its dephasing time T2 which is the theoretical limit for coherently scattered fraction. The next section demonstrates that the response of a resonantly driven two-level system which in our case is represented by an exciton in a seminconductor quantum dot depends significantly on the photon statistics of the exciting light field. Most strikingly, the Mollow triplet which we observe under coherent excitation vanishes under thermal excitation. The second part presents results concerned with the resonantly driven biexciton cascade via two- photon excitation. The coherent interaction between light field and excitons gives rise to a complex five-level system. Here, we show for the first time two-photon Rabi oscillations in the temporal domain. Furthermore, we examine the correlations between the different transitions. The measurements show that we can manipulate the time-ordering of the emitted photons by changing for example the laser power. All these studies share the resonant excitation scheme which allows for a coherent manipulation of the states of the quantum dot and grants access to phenomena typical for resonance fluorescence such as the Mollow triplet and Rabi oscillations. In particular the experiments on photon excitation spectroscopy and the studies on the dressed biexciton cascade show that fundamental effects of quantum optics can be explored in a scalable and application oriented setting using quantum dots.

Xiaoqin Li, Yanwen Wu, Xiaodong Xu +2 more

Transient differential transmission measurements were performed to study coherent dynamics involving the biexciton resonance confined in a single $\mathrm{GaAs}$ quantum dot. When laser pulses with sufficient bandwidth were tuned to cover both the exciton and biexciton transitions, an oscillatory behavior in the probe transmission was observed. These oscillations persist only as long as the pump and probe pulses overlap in time, in contrast to the usual quantum beat phenomena.