  Recently, the negatively charged silicon vacancy centre (SiV) in diamond has
emerged as a novel promising system for quantum information processing (QIP)
due to its superior spectral properties and advantageous electronic structure:
The SiV offers an optically accessible {\Lambda}-type level structure with a
large orbital level splitting even without the need of an external magnetic
field and previous studies determined the ground state coherence time of the
centre to be on the order of 35-45ns. While these studies already indicate the
feasibility of an ultrafast all-optical coherent control of the SiV, no
experimental realization has been presented so far. Here, we report on optical
Rabi oscillations and Ramsey interference between the ground and the excited
state of the SiV using 12 ps long, resonant rotation pulses. Moreover,
utilizing a {\Lambda}-scheme, we demonstrate Raman-based coherent Rabi
rotations and Ramsey interference within the ground state manifold using a
single, 1ps long off-resonant pulse. These measurements prove the accessibility
of the complete set of single-qubit operations relying solely on optical fields
and pave the way for high-speed QIP applications using SiV centres.
