Bulletin of the American Physical Society
48th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 62, Number 8
Monday–Friday, June 5–9, 2017; Sacramento, California
Session T6: Ultracold Plasmas and Molecules |
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Chair: Jacob Roberts, Colorado State University Room: 311-312 |
Friday, June 9, 2017 8:00AM - 8:12AM |
T6.00001: Progress Towards Laser Cooling of an Ultracold Neutral Plasma Thomas Langin, Grant Gorman, Zhitao Chen, Kyle Chow, Thomas Killian We report on progress towards laser-cooling of the ion component of an ultracold neutral plasma (UNP) consisting of $^{88}$Sr$^{+}$. The goal of the experiment is to increase the value of the ion Coulomb Coupling Parameter, $\Gamma_{i}$, which is the ratio of the average nearest neighbor Coulomb interaction energy to the ion kinetic energy. Currently, $\Gamma_{i}$ is limited to $\sim 3$ in most UNP systems. We have developed a new photoionization pathway for plasma creation that starts with atoms in a magnetic trap. This allows us to create much larger plasmas (upwards of $10^9$ atoms with a width of 4 mm). This greatly reduces the plasma expansion rate, giving more time for laser cooling. We have also installed lasers for optically pumping atoms out of dark states that are populated during laser cooling. We will discuss these new systems, along with the results of our first attempts at laser-cooling. [Preview Abstract] |
Friday, June 9, 2017 8:12AM - 8:24AM |
T6.00002: Electron Plasmas Cooled by Cyclotron-Cavity Resonance F. Robicheaux, A.P. Povilus, N.D. DeTal, L.T. Evans, N. Evetts, J Fajans, W.N. Hardy, E.D. Hunter, L. Martens, S. Shanman, C. So, X. Wang, J.S. Wurtele We observe that high-Q electromagnetic cavity resonances increase the cyclotron cooling rate of pure electron plasmas held in a Penning-Malmberg trap when the electron cyclotron frequency, controlled by tuning the magnetic field, matches the frequency of standing wave modes in the cavity. For certain modes and trapping configurations, this can increase the cooling rate by factors of 10 or more. In this talk, we investigate the variation of the cooling rate and equilibrium plasma temperatures over a wide range of parameters, including the plasma density, plasma position, electron number, and magnetic field. [Preview Abstract] |
Friday, June 9, 2017 8:24AM - 8:36AM |
T6.00003: What is the temperature of an ultra-cold Rydberg plasma? Duncan Tate, Gabriel Forest, Yin Li, Edwin Ward, Anne Goodsell We have measured the asymptotic expansion velocities and effective plasma electron temperatures of ultra-cold plasmas (UNPs) which evolve from cold, dense, samples of Rydberg rubidium atoms using ion time-of-flight spectroscopy. A plasma forms when ionization caused by thermal radiation, cold dipole collisions, or hot-cold Rydberg collisions results in a high enough ion density to trap electrons. Thereafter, during the avalanche regime, electron-Rydberg collisions ionize as much as 75\% of the atoms, and the remaining neutral atoms are down-scattered into states of higher binding energy. We find that the amount of energy transferred to the UNP from the Rydberg atoms during the avalanche increases with the initial Rydberg atom binding energy and density. The effective electron temperature is determined when the avalanche ends, i.e., when the adiabatically cooled electrons can no longer ionize the remaining down-scattered Rydberg population. We also find that the dependence of the electron temperature on Rydberg atom density and binding energy gives strong indirect evidence for the existence of a bottleneck in the spectrum of Rydberg states in coexistence with a cold plasma. [Preview Abstract] |
Friday, June 9, 2017 8:36AM - 8:48AM |
T6.00004: Electron strong coupling in low-density ultracold plasmas Wei-Ting Chen, Craig Witte, Jacob Roberts Three-body recombination is one of the main heating mechanisms that prevents electrons in ultracold plasmas (UCPs) from reaching higher degrees of strong coupling. Such heating has been predicted to limit the degree of electron strong coupling in a UCP to strong coupling parameter $\Gamma \sim 0.2$ [F. Robicheaux and James D. Hanson, Phys. Rev. Lett. \textbf{88}, 055002 (2003)]. The recombination rate scales as $\Gamma^{\frac{9}{2}}$ and linearly with plasma frequency. On the other hand, the UCP formation time does not scale linearly with plasma frequency. These two different scaling behaviors with respect to the plasma frequency suggest that by operating at low density, there is a period of time right after formation that the three-body recombination effect is insignificant such that $\Gamma$ can exceed the 0.2 limit temporarily. To experimentally verify this, we measured the temperature and density of low-density UCPs so as to extract $\Gamma$. This was accomplished by measuring an electron oscillation frequency and damping rate. For low-temperature conditions in our system, $\Gamma \sim$ 0.35 was measured. [Preview Abstract] |
Friday, June 9, 2017 8:48AM - 9:00AM |
T6.00005: Temperature measurements in a Yb/Ca dual-species ultracold neutral plasma Tucker Sprenkle, Adam Dodson, Scott Bergeson We report temperature measurement in an expanding dual-species Ca/Yb ultracold neutral plasma. This plasma is formed by sequentially ionizing Ca atoms and Yb atoms in a dual-species magneto-optical trap. We present measurements of the plasma temperature for a range of relative Ca$^+$/Yb$^+$ densities and mixtures, and discuss our results in terms of dynamic shielding in this strongly-coupled Coulomb system. [Preview Abstract] |
Friday, June 9, 2017 9:00AM - 9:12AM |
T6.00006: Ultracold Molecular Assembly Nicholas Hutzler, Lee Liu, Yichao Yu, Jessie Zhang, Jonathan Hood, Kang-Kuen Ni Studies of quantum many-body physics and information rely on the ability to coherently control strongly-interacting quantum objects. Ultracold polar molecules in optical traps are very promising candidates due to their many long-lived internal states and strong, long-range, anisotropic, and highly tunable interactions. A powerful and successful method is to start with ultracold atoms and coherently associate them into ultracold molecules. We take the approach of forming these molecules one-by-one via combining pairs of ultracold atoms in optical tweezers with complete and dynamic control over geometry. The flexibility of this approach allows us to work with NaCs, which has a very large dipole moment of 4.6 D. In this talk, we discuss progress trapping and cooling single atoms, and schemes for molecule formation [arxiv:1701.03121]. [Preview Abstract] |
Friday, June 9, 2017 9:12AM - 9:24AM |
T6.00007: Quantum Reactive Scattering of Ultracold K+KRb Reaction: Universality and Chaotic Dynamics J. F. E. Croft, C. Makrides, M. Li, A. Petrov, B. K. Kendrick, N. Balakrishnan, S. Kotochigova A fundamental question in the study of chemical reactions is how reactions proceed at a collision energy close to absolute zero. This question is no longer hypothetical: quantum degenerate gases of atoms and molecules can now be created at temperatures lower than a few tens of nanoKelvin. In this talk, we discuss the benchmark ultracold reaction between, the most-celebrated ultracold molecule, KRb and K. We report numerically exact quantum-mechanical calculations of the K+KRb reaction on an accurate ab initio ground state potential energy surface of the K$_2$Rb system and compare our results with available experimental data and predictions of universal models. The role of non-additive three-body contributions to the interaction potential is examined and is found to be small for the total reaction rates. However, the rotationally resolved rate coefficients are shown to be sensitive to the short-range interaction potential and follow a Poissonian distribution. [Preview Abstract] |
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