Interferometric Measurements of Many-Body Topological Invariants Using Mobile Impurities

August 8, 2016

Figure 1: Topological polarons*
[Reprinted under a Creative Commons CC-BY license]

Topological quantum phases cannot be characterized by Ginzburg–Landau type order parameters, and are instead described by non-local topological invariants. Experimental platforms capable of realizing such exotic states now include synthetic many-body systems such as ultracold atoms or photons. Unique tools available in these systems enable a new characterization of strongly correlated many-body states.

Prof. Eugene Demler's group, with a colleague from University of Kaiserslautern (Germany) published an article* in Nature Communications in which they propose a general scheme for detecting topological order using interferometric measurements of elementary excitations. According to the authors, the key ingredient is the use of mobile impurities that bind to quasiparticles of a host many-body system. Specifically, the physicists show how fractional charges can be probed in the bulk of fractional quantum Hall systems. They demonstrate that combining Ramsey interference with Bloch oscillations can be used to measure Chern numbers characterizing the dispersion of individual quasiparticles, which gives a direct probe of their fractional charges. Possible extensions of this method to other many-body systems, such as spin liquids, are conceivable.

*See F. Grusdt, N.Y. Yao, D. Abanin, M. Fleischhauer & E. Demler, "Interferometric measurements of many-body topological invariants using mobile impurities," Nature Communications 7:11994 | doi:10.1038/ncomms11994