Observation of quantum criticality with ultracold atoms

Kaden R. A. Hazzard, Erich J. Mueller

Xibo Zhang, Chen-Lung Hung, Shih-Kuang Tung +1 more

Quantum criticality emerges when a many-body system is in the proximity of a continuous phase transition that is driven by quantum fluctuations. In the quantum critical regime, exotic, yet universal properties are anticipated; ultracold atoms provide a clean system to test these predictions. We report the observation of quantum criticality with two-dimensional Bose gases in optical lattices. On the basis of in situ density measurements, we observe scaling behavior of the equation of state at low temperatures, locate the quantum critical point, and constrain the critical exponents. We observe a finite critical entropy per particle that carries a weak dependence on the atomic interaction strength. Our experiment provides a prototypical method to study quantum criticality with ultracold atoms.

Xibo Zhang, Chen-Lung Hung, Shih-Kuang Tung +2 more

Critical behavior developed near a quantum phase transition, interesting in its own right, offers exciting opportunities to explore the universality of strongly correlated systems near the ground state. Cold atoms in optical lattices, in particular, represent a paradigmatic system, for which the quantum phase transition between the superfluid and Mott insulator states can be externally induced by tuning the microscopic parameters. In this paper, we describe our approach to study quantum criticality of cesium atoms in a two-dimensional (2D) lattice based on in situ density measurements. Our research agenda involves testing critical scaling of thermodynamic observables and extracting transport properties in the quantum critical regime. We present and discuss experimental progress on both fronts. In particular, the thermodynamic measurement suggests that the equation of state near the critical point follows the predicted scaling law at low temperatures.

Kaden R. A. Hazzard, Erich J. Mueller

Marion Delehaye, Sébastien Laurent, Igor Ferrier-Barbut +2 more

Summary form only given. Superfluidity is amongst the most impressive macroscopic manifestations of quantum behavior. Frictionless flow has been observed in several low-temperature quantum systems, such as liquid helium [1, 2], or more recently ultracold gases [3-5]. Several hallmarks of superfluidity such as critical velocity, quantized vortices, and second sound have been observed [6-11], in both liquid helium and ultracold gases, and in both Bose and Fermi systems.Here, we use the high level of tunability offered by ultracold gases to control their interactions and obtain a double Bose-Fermi superfluid of fermionic 6Li and bosonic ,Li. We have typically Nf = 3.5 . 105 fermionic atoms and Nb = 4 . 104 bosonic atoms at a temperature of about 100 nK, which is below the critical temperature for superfluidity for both the Bose and the Fermi cloud [13].

Kaden R. A. Hazzard