Showing papers by "Cheng Chin published in 2016"

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

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.

Universal Loss Dynamics in a Unitary Bose Gas

Abstract: The low temperature unitary Bose gas is a fundamental paradigm in few-body and many-body physics, attracting wide theoretical and experimental interest. Here we first present a theoretical model that describes the dynamic competition between two-body evaporation and three-body re-combination in a harmonically trapped unitary atomic gas above the condensation temperature. We identify a universal magic trap depth where, within some parameter range, evaporative cooling is balanced by recombination heating and the gas temperature stays constant. Our model is developed for the usual three-dimensional evaporation regime as well as the 2D evaporation case. Experiments performed with unitary 133 Cs and 7 Li atoms fully support our predictions and enable quantitative measurements of the 3-body recombination rate in the low temperature domain. In particular, we measure for the first time the Efimov inelasticity parameter η * = 0.098(7) for the 47.8-G d-wave Feshbach resonance in 133 Cs. Combined 133 Cs and 7 Li experimental data allow investigations of loss dynamics over two orders of magnitude in temperature and four orders of magnitude in three-body loss. We confirm the 1/T 2 temperature universality law up to the constant η *.

Exotic domain walls in Bose-Einstein condensates with double-well dispersion

Abstract: We study the domain walls which form when Bose condensates acquire a double-well dispersion Experiments have observed such domain walls in condensates driven across a ${\mathbb{Z}}_{2}$ symmetry-breaking phase transition in a shaken optical lattice We derive a generic model to describe the dispersion and to compute the wave functions and energies of the domain walls We find two distinct regimes which demand different physical pictures In the weak-coupling regime, where interactions are weak compared to the kinetic-energy barrier, ``density-wave domain walls'' form that support an extended density wave and a series of phase steps These features can be understood as the quantum interference between domains with distinct momenta In the strong-coupling regime where interaction dominates, the system forms ``phase domain walls'' which have the minimum width allowed by the uncertainty principle and suppressed density modulation Analytic results for the domain-wall wave functions are obtained in the two regimes The energy of domain walls behaves similarly to that of topological defects in paradigmatic field theories