"This project concerns the field of coherent, nonlinear, ultrafast light-matter interaction on a quantum level in solids. It proposes to experimentally explore limits of: i) internal coherence of an individual emitter; ii) radiative coupling between pairs of emitters. A potential long term application of this work could be envisaged, as one can expect that individual emitters could serve as qubits for implementations of optically controlled quantum information processing in solids. As individual emitters we will employ excitons in semiconductors: either bound to impurities or confined in quantum dots. Firstly, by embedding the latter into upright photonic nanowires, that are now available in the team, we will amplify the collection of their coherent optical response by nearly four orders of magnitude as compared to the current state-of-art. This will provide an unprecedented access to their coherent as well as dephasing interaction with phonons. It will also enable retrieval of their n-wave mixing responses to scrutinize coherent couplings within an individual emitter. The second objective is the demonstration of an efficient, controllable and non-local coherent coupling mechanism between distant emitters, which is a prerequisite for the construction of quantum logic gates and networks. Here, such a radiative coupling will be demonstrated and manipulated using resonant emitters embedded into in-plane one-dimensional waveguides, which permit virtually unattenuated propagation of coherence. The internal and propagative coherence of individuals and radiatively coupled pairs will be explored using beyond-the-state-of-the-art methods of coherent nonlinear spectroscopy. Specifically, we will develop a spatially-resolved heterodyne spectral interferometry combined with ultrafast pulse-shaping. The proposed advanced methodology of this ERC project can be associated with techniques developed in other domains, like nuclear magnetic resonance and astrophysics instrumentation."