Observation of Quantum Criticality with Ultracold Atoms in Optical Lattices

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Science  02 Mar 2012:
Vol. 335, Issue 6072, pp. 1070-1072
DOI: 10.1126/science.1217990

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Critically Cold Atoms

Unlike classical phase transitions, such as the freezing of water into ice, which is driven by lowering the temperature of the system, quantum phase transitions occur at absolute zero and are driven by other parameters, including magnetic field or pressure. In the vicinity of a quantum phase transition, a critical region forms where physical observables obey scaling laws as a consequence of the self-similarity of the system. Quantum phase transitions and quantum criticality are usually observed in solid state, but Zhang et al. (p. 1070, published online 16 February) used an optical lattice filled with a cold gas of atoms to simulate a quantum phase transition—from an insulator to a superflnuid in two dimensions. They observed the characteristic scaling of the equation of state, a finding that will facilitate the building of a platform in a tunable system for further investigations of quantum criticality.