UTOPIQ · Ultrafast topological engineering of quantum materials

Topological phases of matter emerge from the interplay between broken symmetries and many-body physics and exhibit many fascinating quantum phenomena. Ultrafast switching between different topological phases using light pulses holds the promise for disruptive optoelectronic functionalities, like dissipationless and fault-tolerant logical operations. However, the lack of proper observable being simultaneously sensitive to the local (in momentum-space) topology of the band structure and compatible with time-resolved measurements prevents the real-time monitoring of ultrafast non-equilibrium topological phase transitions. I will address this fundamental challenge by introducing innovative control and measurement methodologies using tailored light pulses in time-, angle- and polarization-resolved extreme ultraviolet photoemission spectroscopy. This approach will enable to follow the ultrafast evolution of the electronic band structures local topology, in photoexcited quantum materials. This will represent a major advance in photoemission spectroscopy, by moving from band structure mapping to accessing the dynamical evolution of the Bloch wavefunction of solids.I will use these novel time- and quantum-state-resolved dichroic observables to investigate the rich non-equilibrium physics underlying ultrafast topological phase transitions occurring on various timescales following impulsive optical excitation using shaped pump pulses: i) during the formation of hybrid light-matter (Floquet-Bloch) states, ii) upon the transient modification of electronic correlations, and iii) following the excitation of coherent phonon modes. UTOPIQ will deliver a dramatically improved understanding of the interplay between the non-equilibrium behaviour and non-trivial topology in photoexcited quantum materials, while further representing a decisive step towards the development of the field of ultrafast on demand topology.