Abstract
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.
Highlights
A quantum phase transition occurs in a many-body system at absolute zero temperature when a new order smoothly emerges in its ground state [1, 2]
Even though a quantum phase transition happens at zero temperature, the transition influences the finitetemperature properties of the many-body system, which leads to possible experimental observations
Near a quantum phase transition, the many-body system shows universal scaling behaviors, termed as quantum criticality, with characteristic scaling exponents determined by basic properties of the system, such as symmetry and dimensionality [1]
Summary
A quantum phase transition occurs in a many-body system at absolute zero temperature when a new order smoothly emerges in its ground state [1, 2]. In a system of bosonic atoms confined in optical lattices, the superfluid-to-Mott insulator transition, described by the BoseHubbard model [3], is ideal for studying quantum criticality In this system, the two competing energy scales are the tunneling energy t and the on-site interaction U. Based on high-resolution in situ absorption imaging, we can record density profiles and fluctuations of the sample in equilibrium, which allows us to identify critical scaling laws of thermodynamic observables and compare to the theoretical predictions. Another direction is to initiate a dynamic passage to the quantum critical regime, from which we attempt to extract dynamical critical exponents and quantum transport coefficients. We will discuss the “scaling” and the “dynamics” approaches separately
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