Ultrafast phenomena related to and/or accessible only via the absolute temporal phase of electronic, vibrational and spin coherent excitations in condensed matter are studied via electromagnetic transients in the multi-terahertz regime. The project also includes innovative aspects of quantum optics, femtosecond lasers and terahertz technology. Four central objectives are as follows:(i) Establishing rapid quantum oscillatory motion as the earliest regime in the dynamics and transport of electrons in solids. Fundamental phenomena like the temporal buildup of effective mass in semiconductors and Zitterbewegung in graphene are accessed directly.(ii) Studying nonclassical light emission predicted to emerge after non-adiabatic perturbation of ultrastrongly coupled systems of light and matter. The quantum properties of radiation released by such processes are investigated at the uncertainty limit between amplitude and phase of the light field.(iii) Observation and control of charge and spin electronic properties of solids under extremely high transient electric or magnetic bias provided by a novel source of phase-locked multi-terahertz pulses allowing analysis with a resolution significantly below half a cycle of light.(iv) Field-resolved photon-echo studies in the mid infrared. Unprecedented insights into complex phenomena like the interplay between low-energy degrees of freedom in high-temperature superconductors and intermolecular motion in liquids are envisioned.New developments in ultrabroadband terahertz technology will enable the experiments:(a) Generation of phase-locked electromagnetic transients with precisely controlled shape of the electric field like quasi-monopolar terahertz shock waves or single-cycle pulses with field amplitudes up to 30 MV/cm.(b) Coherent detection of electric fields with bandwidth up to 200 THz and sensitivity at the uncertainty limit, giving access to the quantum properties of electromagnetic waves in amplitude and phase.