Historically, electron spin resonance (ESR) has provided excellent insight into the electronic, magnetic, and chemical structure of samples hosting spin centers. In particular, the hyperfine interaction between the electron and the nuclear spins yields valuable structural information about these centers. In recent years, the combination of ESR and scanning tunneling microscopy (ESR-STM) has allowed to acquire such information about individual spin centers of magnetic atoms bound atop a surface, while additionally providing spatial information about the binding site. Here, we conduct a full angle-dependent investigation of the hyperfine splitting for individual hydrogenated titanium atoms on MgO/Ag(001) by measurements in a vector magnetic field. We observe strong anisotropy in both the g factor and the hyperfine tensor. Combining the results of the hyperfine splitting with the symmetry properties of the binding site obtained from STM images and a basic point charge model allows us to predict the shape of the electronic ground state configuration of the titanium atom. Relying on experimental values only, this method paves the way for a new protocol for electronic structure analysis for spin centers on surfaces.@en

This thesis presents experiments on the free, coherent spin dynamics ofmagnetic nanostructures built out of individual titanium atoms adsorbed on bilayer MgOislands grown on a Ag(100) crystal inside a scanning tunneling microscope (STM).We use the exchange field of the spin-polarized probe tip to tune the eigenstates of the magnetic structures to superpositions of the Zeeman product states. These superpositions appear as avoided level crossings of the eigenenergies as a function of tip-atom distance and are detected through electron spin resonance (ESR) measurements. Subsequently,we put the STMtip at the position where we detect an avoided crossing and we perform a DC pump-probe experiment. Here, the pump pulse causes a single spin flip on the atom under state tip which is then allowed to evolve freely for some time t until it is measured by the subsequent probe pulse. By varying the time t between pump and probe over many experiments, we are able to trace out the evolution of the spin under the tip with nanosecond time resolution....@en

Full insight into the dynamics of a coupled quantum system depends on the ability to follow the effect of a local excitation in real-time. Here, we trace the free coherent evolution of a pair of coupled atomic spins by means of scanning tunneling microscopy. Rather than using microwave pulses, we use a direct-current pump-probe scheme to detect the local magnetization after a current-induced excitation performed on one of the spins. By making use of magnetic interaction with the probe tip, we are able to tune the relative precession of the spins. We show that only if their Larmor frequencies match, the two spins can entangle, causing angular momentum to be swapped back and forth. These results provide insight into the locality of electron spin scattering and set the stage for controlled migration of a quantum state through an extended spin lattice.@en