Quantum networks lie at the heart of distributed quantum computing and secure quantum communication - research areas that have seen a strong increase of interest over the last decade. Their basic architecture consist of stationary nodes composed of quantum processors which are linked via photonic channels. The key requirement, and at the same time the most demanding challenge, is the efficient distribution of entanglement between distant nodes. The two ground states of single spins confined in self-assembled InGaAs quantum dots provide an effective two-level system for the implementation of quantum bits. Moreover, they offer strong transition dipole moments with outstanding photonic properties allowing for the realisation of close to ideal, high-bandwidth spin-photon interfaces. These properties are combined with the benefits of working in the solid state, such as scalability and integrability of devices, to form a promising candidate for the implementation of fast entanglement distribution. In this dissertation we provide the first implementation of a unit cell of a quantum network based on single electron spins in InGaAs. We use a probabilistic scheme based on spin-photon entanglement and the erasure of which path information to project the two distant spins into a maximally entangled Bell state. The successful generation of entanglement is verified through a reconstruction of the final two-spin state and we achieve an average fidelity of $61.6\pm2.3\%$ at a record-high generation rate of $5.8\,\mathrm{kHz}$. One of the main constraints to the achieved fidelity is the limited coherence of the electron spin. We show that it can be extended by three orders of magnitude through decoupling techniques and develop a new measurement technique, allowing us to investigate the origins of the decoherence which has previously been obscured by nuclear feedback processes. Our results evidence that further extension of coherence is ultimately limited by intrinsic mechanisms closely related to local strain due to the growth method of self-assembled quantum dots. After establishing the intrinsic limits to the electron coherence we investigate the coherence properties of the single hole spin as an alternative two-level system with the potential for higher coherence times. We show that the hole spin coherence is indeed superior to the one of the electron and realise the first successful dynamic decoupling scheme implemented in these systems. We find that the decoherence at low external magnetic fields is still governed by coupling to the nuclear spins whereas it is dominated by electrical noise for fields exceeding a few Tesla. This noise source is extrinsic to the quantum dots and a better understanding offers the potential for further improvement of the coherence time. The findings of this work present a complete study of the coherence of the charge carriers in self-assembled quantum dots and provide the knowledge needed to improve the implementation of a quantum-dot based quantum network. In particular, the combination of spin-spin entanglement and the hole coherence times enable further research towards multidimensional photonic cluster states.

<p><br></p><p dir="ltr">Over the past decade, optical frequency combs have spurred significant advancements in both classical ultrafast optics and quantum optics. My research contributes to these two fields, catering to applications in precision metrology and optical networking. In the domain of quantum optics, the study delves into biphoton frequency combs with time-energy entanglement, employing novel electro-optic modulation schemes to enhance sensitivity and enable precise measurements of temporal correlations. Additionally, Bell states, a crucial class of entangled quantum bases, are generated in the frequency domain, showcasing their utility in delay metrology and quantum cryptographic protocols. </p><p dir="ltr">In the realm of classical optical frequency combs, this work explores dynamic steering of pulsed optical beams, holding promise for applications in imaging and remote sensing. The concept of time-efficient dynamic beam steering using a spatial array of optical frequency combs is elucidated and experimentally demonstrated through the utilization of a high-resolution spectral disperser, specifically a virtually imaged phased array (VIPA). Furthermore, integrated photonic designs featuring wavelength-selective switches and spectral dispersers are proposed to enable a versatile on-chip implementation of the beam steering approach. In sum, this research leverages the capabilities of classical and quantum optical frequency combs, with implications for emerging applications such as distributed sensing, quantum networking, and light detection and ranging (LIDAR).</p>