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Universal space-time scaling symmetry in the dynamics of bosons across a quantum phase transition

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Science  04 Nov 2016:
Vol. 354, Issue 6312, pp. 606-610
DOI: 10.1126/science.aaf9657

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Shaking the lattice uncovers universality

Most of our knowledge of quantum phase transitions (QPTs)—which occur as a result of quantum, rather than thermal, fluctuations—comes from experiments performed in equilibrium conditions. Less is known about the dynamics of a system going through a QPT, which have been hypothesized to depend on a single time and length scale. Clark et al. confirmed this hypothesis in a gas of cesium atoms in an optical lattice, which was shaken progressively faster to drive the gas through a QPT.

Science, this issue p. 606

Abstract

The dynamics of many-body systems spanning condensed matter, cosmology, and beyond are hypothesized to be universal when the systems cross continuous phase transitions. The universal dynamics are expected to satisfy a scaling symmetry of space and time with the crossing rate, inspired by the Kibble-Zurek mechanism. We test this symmetry based on Bose condensates in a shaken optical lattice. Shaking the lattice drives condensates across an effectively ferromagnetic quantum phase transition. After crossing the critical point, the condensates manifest delayed growth of spin fluctuations and develop antiferromagnetic spatial correlations resulting from the sub-Poisson distribution of the spacing between topological defects. The fluctuations and correlations are invariant in scaled space-time coordinates, in support of the scaling symmetry of quantum critical dynamics.

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