QUROPE Quantum Information Processing and Communication in Europe

Ultrafast pump-probe spectroscopy is employed to directly monitor the tunneling of charge carriers from single and vertically coupled quantum dots and probe intra-molecular dynamics. Immediately after resonant optical excitation, several peaks are observed in the pump-probe spectrum arising from Coulomb interactions between the photogenerated charge carriers. The influence of few-Fermion interactions in the photoexcited system and the temporal evolution of the optical response is directly probed in the time domain.

By employing various high-resolution metrology techniques we directly probe the material composition profile within GaAs–Al0.3Ga0.7As core–shell nanowires grown by molecular beam epitaxy on silicon. Micro Raman measurements performed along the entire (>10 μm) length of the 111-oriented nanowires reveal excellent average compositional homogeneity of the nominally Al0.3Ga0.7As shell.

Accessing fundamental structure-property correlations in ternary semiconductor nanowires is a challenging endeavor often limited by large compositional inhomogeneities. Here, we investigate strongly periodic In1−xGaxAs nanowire arrays grown on Si with very high compositional uniformity to identify the role of microstructural features (crystal phase and stacking order) on the phonon and optical properties via transmission electron microscopy, Raman, and photoluminescence spectroscopy.

We report the routing of quantum light emitted by self-assembled InGaAs quantum dots (QDs) into the optical modes of a GaAs ridge waveguide and its efficient detection on-chip via evanescent coupling to NbN superconducting nanowire single photon detectors (SSPDs). The waveguide coupled SSPDs primarily detect QD luminescence, with scattered photons from the excitation laser onto the proximal detector being negligible by comparison.

The ability to control and exploit quantum coherence and entanglement drives research across many fields ranging from ultra-cold quantum gases to spin systems in condensed matter. Transcending different physical systems, optical approaches have proven themselves to be particularly powerful, since they profit from the established toolbox of quantum optical techniques, are state-selective, contact-less and can be extremely fast.

We study various techniques to characterize the quantum states of a strongly dissipative system, namely, the an-harmonic oscillator. One cannot directly access the quantum states themselves but only transitions between them. Various methods bring various advantages and inconvenients. We compare several observables under coherent and incoherent excitation.

Abstract. A scheme to observe direct experimental evidence of Jaynes–Cummings nonlinearities in a strongly dissipative cavity quantum electrodynamics system was devised. In such a system, large losses compete with the strong light-matter interaction. Comparing coherent and incoherent excitations of the system, it was shown that resonant excitation of the detuned emitter makes it possible to evidence few photon quantum nonlinearities in currently available experimental systems.

We apply ultrafast pump-probe photocurrent spectroscopy to directly probe few Fermion charge and spin dynamics in an artificial molecule formed by vertically stacking a pair of InGaAs self-assembled quantum dots. As the relative energy of the orbital states in the two dots are energetically tuned by applying static electric fields, pronounced anticrossings are observed arising from electron tunnel couplings.

We employ ultrafast pump-probe spectroscopy with photocurrent readout to directly probe the dynamics of a single hole spin in a single, electrically tunable self-assembled quantum dot molecule formed by vertically stacking (In,Ga)As quantum dots. Excitons with defined spin configurations are initialized in one of the two dots using circularly polarized picosecond pulses. The time-dependent spin configuration is probed by the spin selective optical absorption of the resulting few fermion complex.