Physics Colloquia

Topological quantum computing offers a route to lower error rates, enabling fault tolerance and impactful applications. However, it relies on reliably tuning devices into a non-Abelian topological phase. In this talk, I will discuss four lessons that have been learned in the attempt to realize a topological quantum computer.

Once in a while, a discovery comes along that opens up uncharted paths of inquiry. The discovery of atomically thin crystals, starting with graphene and followed up with dozens in the van der Waals family of compounds, has changed the way we think about materials. This new class of designer materials is making it possible to tune and control electronic properties without changing chemical composition, through alternative means such as superposing different layers, misaligning them, inducing strain, etc. In this talk I will describe highlights from this rapidly evolving field, from its serendipitous inception, to the discovery of correlated electron phases in buckled and twisted layers.

1. G. Li et al Observation of Van Hove singularities in twisted graphene layers, Nature Physics 6, 109 (2009)
2. J. Mao et al, Evidence of Flat Bands and Correlated States in Buckled Graphene Superlattices, Nature 584, 215 (2020)
3. S.Wu, Z. Zhang, K. Watanabe, T. Taniguchi, E.Y. Andrei, Chern Insulators and Topological Flat-bands in Magic-angle Twisted Bilayer Graphene , Nature Materials 20, 488 (2021)

The string theory landscape of vacua points to new consistency conditions that a quantum gravitational system must satisfy. There are only a small number of quantum field theories that satisfy these conditions and all the rest belong to the "Swampland," which cannot be consistently coupled to gravity. In this talk I review some of these conditions and their implications for cosmology and particle physics.