Scaling symmetry of topological defects in quantum critical dynamics

Spanning condensed matter, cosmology, and quantum gases, evolution of many-body systems is hy-pothesized to be universal near a continuous phase transition. A long-sought signature of the universal dynamics is the scaling symmetry of emerging topological defects; examples include cosmic domains in early universe (T. Kibble, 1976), and vortices in quenched superfluid helium (W. Zurek, 1985).  We test the scaling symmetry and universality of quantum critical dynamics based on Bose-Einstein condensates of cesium atoms ramping across an effective ferromagnetic quantum phase transition. We observe a sudden growth of quantum fluctuations and domains separated by topological defects (domain walls). Intriguingly, the domains are anti-ferromagnetically ordered with record thermal energy scales as low as kB x 20pK. Time and length scales measured over a wide range of parameters yield precise temporal and spatial critical exponents of 0.50(2) and 0.26(2), respectively, consistent with theory. In the scaled space-time coordinate, correlations collapse to a single curve, in support of the universality hypothesis.