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Universal Signatures of Fractionalized Quantum Critical Points

Groundstates of certain materials can support exotic excitations with a charge that's a fraction of the fundamental electron charge. The condensation of these fractionalized particles has been predicted to drive novel quantum phase transitions, which haven't yet been observed in realistic systems. Through numerical and theoretical analysis of a physical model of interacting lattice bosons, we establish the existence of such an exotic critical point, called XY*. We measure a highly non-classical critical exponent eta = 1.49(2), and construct a universal scaling function of winding number distributions that directly demonstrates the distinct topological sectors of an emergent Z_2 gauge field. The universal quantities used to establish this exotic transition can be used to detect other fractionalized quantum critical points in future model and material systems.