Measuring topological invariants in few-level quantum system
Understanding topological nature of physical system is one of the most important topics in modern physics. In condense matter, non-trivial topological phase is characterized by non-zero Chern number. In particle physics, solitons and monopole solutions of non-Abelian gauge theories are characterized by their topological charges. Here, we prepared few-level quantum system by dressing hyperfine ground states of 87Rb with radio frequency and microwave fields, and measured the first Chern number in parameter space by observing non-adiabatic response due to local Berry curvature. The non-zero value of the topological invariants can be understood as resulting from monopole sources.