Showing papers by "Cheng Chin published in 2014"

Geometric scaling of Efimov states in a ⁶Li-¹³³Cs mixture.

Abstract: In few-body physics, Efimov states are an infinite series of three-body bound states that obey universal discrete scaling symmetry when pairwise interactions are resonantly enhanced. Despite abundant reports of Efimov states in recent cold atom experiments, direct observation of the discrete scaling symmetry remains an elusive goal. Here we report the observation of three consecutive Efimov resonances in a heteronuclear Li-Cs mixture near a broad interspecies Feshbach resonance. The positions of the resonances closely follow a geometric series 1, λ, λ². The observed scaling constant λ(exp)=4.9(4) is in good agreement with the predicted value of 4.88.

Strong interaction effects and criticality of bosons in shaken optical lattices.

Abstract: We study the quantum phase transitions and identify a tricritical point between a normal Bose superfluid, a superfluid that breaks additional ${Z}_{2}$ Ising symmetry, and a Mott insulator in a recent shaken optical lattice experiment. We show that near the transition between normal and ${Z}_{2}$ symmetry breaking superfluids, bosons can condense into a momentum state with high or even locally maximum kinetic energies due to the interaction effect. We present a general low-energy effective field theory that treats both the superfluid transition and the Ising transition in a uniform framework. Using the perturbative renormalization group method, we find that the critical behavior of the quantum phase transition belongs to a universality class different from that of a dilute Bose gas.

Bosonic thermoelectric transport and breakdown of universality

Abstract: We discuss the general principles of transport in normal phase atomic gases, comparing Bose and Fermi systems. Our study shows that two-dimensional bosonic transport is non-universal with respect to different dissipation mechanisms. Near the superfluid transition temperature Tc, a striking similarity between the fermionic and bosonic transport emerges because super-conducting (fluid) fluctuation transport for Fermi gases is dominated by the bosonic, Cooper pair component. As in fluctuation theory, one finds that the Seebeck coefficient changes sign at Tc and the Lorenz number approaches zero at Tc. Our findings appear quantitatively consistent with recent Bose gas experiments.

Efficient Continuous-Duty Bitter-Type Electromagnets for Cold Atom Experiments

Abstract: We present the design, construction, and characterization of Bitter-type electromagnets which can generate high magnetic fields under continuous operation with efficient heat removal for cold atom experiments. The electromagnets are constructed from a stack of alternating layers consisting of copper arcs and insulating polyester spacers. Efficient cooling of the copper is achieved via parallel rectangular water cooling channels between copper layers with low resistance to flow; a high ratio of the water-cooled surface area to the volume of copper ensures a short length scale (~1 mm) to extract dissipated heat. High copper fraction per layer ensures high magnetic field generated per unit energy dissipated. The ensemble is highly scalable and compressed to create a watertight seal without epoxy. From our measurements, a peak field of 770 G is generated 14 mm away from a single electromagnet with a current of 400 A and a total power dissipation of 1.6 kW. With cooling water flowing at 3.8 l/min, the coil temperature only increases by 7 °C under continuous operation.

Observation of geometric scaling of Efimov states in a Fermi-Bose Li-Cs mixture

Abstract: In few-body physics, Efimov states are an infinite series of three-body bound states that obey universal discrete scaling symmetry when pairwise interactions are resonantly enhanced. Despite abundant reports of Efimov states in recent cold atom experiments, direct observation of the discrete scaling symmetry remains an elusive goal. Here we report the observation of three consecutive Efimov resonances in a heteronuclear Li-Cs mixture near a broad interspecies Feshbach resonance. The positions of the resonances closely follow a geometric series $1$, $\lambda$, $\lambda^2$. The observed scaling constant $\lambda_{\rm exp} = 4.9(4)$ is in good agreement with the predicted value of 4.88.