arXiv subjects

S. Tung

Publications and source records attributed to S. Tung.

9 recordsLinked to original sources

arXiv2023

Preparing pure $^{43}$Ca$^+$ samples in an ion trap with photoionization and parametric excitations

We present a practical scheme for the efficient preparation of laser-cooled $^{43}$Ca$^+$ ions in an ion trap. Our approach integrates two well-established methods: isotope-selective photoionization and isotope-specific parametric excitation. Drawing inspiration from the individual merits of each method, we have successfully integrated these techniques to prepare extended chains of $^{43}$Ca$^+$ ions, overcoming the challenge posed by their low natural abundance of 0.135\% in a natural source. Furthermore, we explore the subtleties of our scheme, focusing on the influence of different factors on the purification process. Our investigation contributes to a broader understanding of the technique and highlights the adaptability of established methods in addressing specific isotopic challenges.

physics.atom-ph↗

arXiv2023

Dual-species Bose-Einstein condensates of $^{7}$Li and $^{133}$Cs

We report the creation of dual-species Bose-Einstein condensates (BECs) of $^{7}$Li and $^{133}$Cs. These BECs are formed in a bichromatic optical dipole trap created with 1550-nm and 780-nm laser beams. During the production process, an external magnetic field of 886~G is applied to adjust the scattering lengths to $a_{\rm{Cs}} = 123a_0$, $a_{\rm{Li}} = 484a_0$, and $a_{\rm{LiCs}} = 248a_0$. These scattering lengths allow for efficient evaporation and sympathetic cooling. The dual-species BECs are typically produced with $1.5\times 10^4$ Cs atoms and $6.0\times 10^3$ Li atoms. This quantum degenerate mixture of Li and Cs provides an ideal platform for exploring phenomena such as polarons and Efimov trimers, as well as for creating ground-state LiCs molecules.

cond-mat.quant-gas↗

arXiv2022

Feshbach resonances in an ultracold $^{7}$Li-$^{133}$Cs Bose-Bose mixture

We present a study of interspecies Feshbach resonances in ultracold $^{7}$Li-$^{133}$Cs Bose-Bose mixtures. We locate ten interspecies resonances in three different spin-state combinations. By comparing to coupled-channel calculations, we assign six of the resonances to $s$-wave channels and the rest to $p$-wave channels. We use the $s$-wave resonances to refine the ground-state potentials of LiCs in the coupled-channel calculations and then obtain an accurate characterization of the scattering and bound-state properties of the mixtures. Our results will be useful for future experiments with ultracold $^{7}$Li-$^{133}$Cs mixtures.

cond-mat.quant-gas↗

arXiv2021

Lithium-cesium slow beam from a two-dimensional magneto-optical trap

We present the creation of a lithium-cesium slow beam using a two-dimensional magneto-optical trap. The two-species atomic beam is directed to load a three-dimensional magneto-optical trap in ultrahigh vacuum. We achieve a loading rate of 1.3$\times$10$^{7}$ lithium atoms/s with the lithium oven temperature at 370~$^{\circ}$C and 2.2$\times$10$^{7}$ cesium atoms/s with the Cs oven temperature at 20~$^{\circ}$C. The maximum numbers of lithium and cesium atoms in the trap are 1.0$\times$10$^{9}$ and 1.4$\times$10$^{8}$, respectively. Our results show that the simple and compact two-dimensional magneto-optical trap is suitable for producing an atomic beam of two species that have a large mass ratio and very different volatilities.

physics.atom-ph↗

arXiv2010

Observation of the Presuperfluid Regime in a Two-Dimensional Bose Gas

In complementary images of coordinate-space and momentum-space density in a trapped 2D Bose gas, we observe the emergence of pre-superfluid behavior. As phase-space density $ρ$ increases toward degenerate values, we observe a gradual divergence of the compressibility $κ$ from the value predicted by a bare-atom model, $κ_{ba}$. $κ/κ_{ba}$ grows to 1.7 before $ρ$ reaches the value for which we observe the sudden emergence of a spike at $p=0$ in momentum space. Momentum-space images are acquired by means of a 2D focusing technique. Our data represent the first observation of non-meanfield physics in the pre-superfluid but degenerate 2D Bose gas.

cond-mat.quant-gas↗

arXiv2007

Vortex proliferation in the Berezinskii-Kosterlitz-Thouless regime on a two-dimensional lattice of Bose-Einstein condensates

We observe the proliferation of vortices in the Berezinskii-Kosterlitz-Thouless regime on a two-dimensional array of Josephson-coupled Bose-Einstein condensates. As long as the Josephson (tunneling) energy J exceeds the thermal energy T, the array is vortex-free. With decreasing J/T, vortices appear in the system in ever greater numbers. We confirm thermal activation as the vortex formation mechanism and obtain information on the size of bound vortex pairs as J/T is varied.

cond-mat.mes-hall↗

arXiv2006

Observation of Vortex Pinning in Bose-Einstein Condensates

We report the observation of vortex pinning in rotating gaseous Bose-Einstein condensates (BEC). The vortices are pinned to columnar pinning sites created by a co-rotating optical lattice superimposed on the rotating BEC. We study the effects of two different types of optical lattice, triangular and square. With both geometries we see an orientation locking between the vortex and the optical lattices. At sufficient intensity the square optical lattice induces a structural cross-over in the vortex lattice.

cond-mat.other↗

arXiv2004

Vortex Lattice Dynamics in Rotating Spinor Bose-Einstein Condensates

We observe interlaced square vortex lattices in rotating two-component dilute-gas Bose-Einstein condensates (BEC). After preparing a hexagonal vortex lattice in a single-component BEC in an internal state $|1>$ of $^{87}$Rb atoms, we coherently transfer a fraction of the superfluid to a different internal state $|2>$. The subsequent evolution of this pseudo-spin-1/2 superfluid towards a state of offset square lattices involves an intriguing interplay of phase-separation and -mixing dynamics, both macroscopically and on the length scale of the vortex cores, and a stage of vortex turbulence. Stability of the square lattice structure is confirmed via the application of shear perturbations, after which the structure relaxes back to the square configuration. We use an interference technique to show the spatial offset between the two vortex lattices. Vortex cores in either component are filled by fluid of the other component, such that the spin-1/2 order parameter forms a Skyrmion lattice.

cond-mat.other↗

arXiv2004

Experimental studies of equilibrium vortex properties in a Bose-condensed gas

We characterize several equilibrium vortex effects in a rotating Bose-Einstein condensate. Specifically we attempt precision measurements of vortex lattice spacing and the vortex core size over a range of condensate densities and rotation rates. These measurements are supplemented by numerical simulations, and both experimental and numerical data are compared to theory predictions of Sheehy and Radzihovsky [17] (cond-mat/0402637) and Baym and Pethick [25] (cond-mat/0308325). Finally, we study the effect of the centrifugal weakening of the trapping spring constants on the critical temperature for quantum degeneracy and the effects of finite temperature on vortex contrast.

cond-mat.soft↗