Generation of high fidelity entanglement between quantum nodes is a key component of a future quantum internet. Heralded entanglement generation of two spatially separated qubit nodes can be established by interference and measurement of two photons, each entangled with one qubit state. The two-node entanglement fidelity is limited by the degree of indistinguishability of the photons, which can be measured in a Two-Photon Quantum Interference (TPQI) experiment. In this thesis, a TPQI experiment has been performed with photons emitted by a single Nitrogen-Vacancy (NV) center. This self-interference experiment shows a visibility of V=0.91±0.02 and a photon indistinguishability of J=0.945 in the Monte-Carlo method obtained 1σ-confidence interval of [0.920, 0.966] after correction for system imperfections, demonstrating near-perfect indistinguishability of zero-phonon line photons emitted by a single NV center. Furthermore, an extensive TPQI model was developed that includes possible arrival time- and frequency differences of the photons. This model predicts a dark- and noise count limited V=0.79±0.06 for a future two-node NV TPQI experiment with quantum frequency-converted photons, at a distinguishable photon coincidence rate of 1.2mHz, allowing for an experimentally feasible double-click two-node entanglement fidelity of 0.89±0.03.

In this research, the effect of Chiral Induced Spin Selectivity is studied by means of a transport calculation on a model of a chiral molecule between two gold contacts. The method consists of two main parts: optimizing the geometry of the entire system, being the molecule and the contacts, and performing the transport calculation on the system, which yields the density of states and the transmission over the energy range of -0.5 to 0.0 Hartree.

The geometry optimization is performed in two ways: in the first approach the entire system is optimized under the constraints that the y- and z-coordinates of the atoms of the contacts are frozen, in the second approach the atoms of the contacts are completely frozen on their initial positions. The first approach did not conserve the periodic structure of the gold lattice. The second approach yielded a geometrically optimized system with correct contacts.

The transport calculation is performed on the three systems, being the non-optimized system, the system optimized by the first method and the system optimized by the second method. There was no spin selectivity found: the density of states as well as the transmission are exact copies for the two spin orientations, which is the consequence of a spin-restricted transport calculation.

The density of states for the three systems are similar. The highest occupied molecular orbital as well as the lowest unoccupied molecular orbital were found to be situated just below and above the Fermi energy of the contacts, respectively, which is consistent with literature.
The transmission of the three systems show greater variation. The systems with optimized geometries have a constant transmission close to zero around the Fermi energy of the contacts. The non-optimized system has a fluctuating transmission above zero around this energy.

Based on these findings, a spin-unrestricted transport calculation including a spin-orbit ZORA-key is proposed. In order to speed up calculations, it is also recommended to apply the Wide Band Limit.