Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session G35: Dipolar Gases, Rydberg Atoms, Cold Molecules, and Few-body Systems |
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Sponsoring Units: DAMOP Chair: Colin Parker, University of Chicago Room: 210B |
Tuesday, March 3, 2015 11:15AM - 11:27AM |
G35.00001: Roton phenomena and stability properties of dipolar condensates Aleksey Fedorov, Igor Kurbakov, Yurii Lozovik Experimental and theoretical studies of novel quantum phenomena in dipolar systems have a great impact for atomic physics. These systems provide an interface between physics of strongly and weakly correlated matter. Being typical for strongly correlated systems, the roton-maxon excitation spectrum, originally observed in superfluid helium, occurs to appear in a weakly interacting dipolar gases. In this contribution, two dipolar bosonic systems are under consideration: dipolar excitons in semiconductor layers of heterostructures and tilted dipolar particles in a quantum layer. In weak correlation regime, we predict a generation of the roton-maxon excitation spectrum for BEC of dipolar excitons in a semiconductor layer. We discuss observation of the roton-maxon spectrum for exciton BEC in GaAs heterostructures. We calculate the stability diagrams for 2D tilted bosonic dipolar particles in a quantum layer. Breaking of the rotational symmetry for a system of tilted dipoles leads to the convergence of the condensate depletion even up to the threshold of the roton instability, with mean-field approach being valid. We discuss observation of these effects in experiments with ultracold atoms and polar molecules. [Preview Abstract] |
Tuesday, March 3, 2015 11:27AM - 11:39AM |
G35.00002: Dipolar Quasi-2D Bosons with Non-zero Dipole Tilt Angle Pengtao Shen, Khandker Quader We study properties of dipolar bosons in quasi-2D geometry, with dipoles oriented at an angle to the direction perpendicular to the confining 2D plane. Starting from time-dependent Gross-Pitaevski equations, and the resulting Bogoliubov-de Gennes equations, we calculate the excitation spectrum of the Bose-Einstein condensate, and explore possible instabilities of the system as the tilt angle, system density and the relative strength of the dipole-dipole interaction are varied. We study how the depletion of the condensate varies with respect to these parameters. We also explore the effect of the anisotropic dipolar interaction on results in different momentum directions. [Preview Abstract] |
Tuesday, March 3, 2015 11:39AM - 11:51AM |
G35.00003: Half-Quantum Vortex Molecules in a Binary Dipolar Bose Gas Ryan Wilson, Wilbur Shirley, Brandon Anderson, Charles Clark We discuss the ground state phases of a rotating two-component, or binary Bose-Einstein condensate, wherein one component possesses a large permanent magnetic dipole moment. A variety of non-trivial phases emerge in this system, including a half-quantum vortex (HQV) chain phase and a HQV molecule phase, where HQVs bind at short distances. We attribute these phases to the development of a minimum in the HQV interaction potential, which emerges without coherent coupling or attractive interactions between the components. Thus, we show that the presence of dipolar interactions in this system provides a unique mechanism for the formation of HQV molecules and results in a rich ground state phase diagram. [Preview Abstract] |
Tuesday, March 3, 2015 11:51AM - 12:03PM |
G35.00004: Competing instabilities of a Dipolar Fermi Gas Ahmet Keles, Erhai Zhao Recent experiments in the cold atom Fermi gas have explicitly shown the deformation of the Fermi surface in the presence of long range dipolar interactions. Motivated by this, we investigate the competing instabilities of a dipolar Fermi gas within the functional renormalization group. We analyze the flow of the effective action in the particle-particle as well as particle-hole channel, consider the self energy term, and discuss the interplay of different instabilities at low temperatures. [Preview Abstract] |
Tuesday, March 3, 2015 12:03PM - 12:15PM |
G35.00005: Rydberg facilitated charge transport in an optical lattice Rick Mukherjee, Igor Lesanovsky, Thomas Pohl We study the dynamics of a single ion trapped in a lattice that is otherwise filled with neutral atoms. For typical lattice spacings, there exist highly excited electronic (Rydberg) states in which the ion and an adjacent atom form a charged molecule. We show that the laser coupling to these molecular Rydberg states induces a charge exchange dynamics which effectively results in the transport of the ion through the lattice. The character of the transport crucially depends on the coupling between the electronic dynamics and the vibrational motion of the atoms and ion. We formulate a criterion for distinguishing coherent and incoherent regimes and demonstrate that aspects of the transport dynamics such as its direction can be controlled by the excitation laser. [Preview Abstract] |
Tuesday, March 3, 2015 12:15PM - 12:27PM |
G35.00006: Photonic Controlled-Phase Gate Based on Rydberg Interactions Mohammadsadegh Khazali, Khabat Heshami, Christoph Simon Photons are ideal carriers of information in quantum communication. Since they do not interact, the implementation of deterministic photonic quantum computation depends on the creation of a non-permanent strong interaction between single photons. The implementation of neutral Rydberg atom gates inspired the development of photonic gates, using the coherent reversible mapping of the quantum states of photons onto highly interacting Rydberg atoms. Here we propose an interaction-based two-qubit gate between photons stored in Rydberg levels of an atomic ensemble.\footnote{M. Khazali, K. Heshami, C. Simon, arXiv:1407.7510 (2014)} We perform a detailed study of errors due to the many-body interaction between Rydberg spin-waves, and we propose a compensation scheme for these errors. Furthermore we completely separate interaction and propagation by eliminating the Rydberg level from the storage process. Our proposed controlled-phase gate can achieve 99{\%} fidelity with current technology. [Preview Abstract] |
Tuesday, March 3, 2015 12:27PM - 12:39PM |
G35.00007: Rydberg Impurity Probes in Ultracold Gases Mark Mitchison, Tomi Johnson, Martin Plenio, Dieter Jaksch Impurities immersed in ultracold gases can act as highly sensitive, tunable and potentially non-destructive probes of their environment. In this setting, we propose the use of an atomic impurity in a Rydberg state to measure density fluctuations via Ramsey interferometry. The rapid collisional dynamics of the light Rydberg electron interacting with the heavy gas particles, combined with the capability to quickly change the state of the impurity with optical pulses, make such a probe ideal for measuring local properties of ultracold gases. Our proposed device promises angle-resolved density measurements with sub-micron spatial resolution, and with no need to integrate over the line of sight. We outline how Rydberg impurity probes could be applied to study various interesting quantum states of current experimental relevance. We also discuss the possibility of using multiple Rydberg atoms to extract the spatial pair distribution function $g^{(2)}($\textbf{\textit{r}}). Our work is placed in the context of other recently proposed impurity-based probes. [Preview Abstract] |
Tuesday, March 3, 2015 12:39PM - 12:51PM |
G35.00008: Revealing the origin of super-Efimov states in the hyperspherical formalism Chao Gao, Jia Wang, Zhenhua Yu Quantum effects can give rise to exotic Borromean three-body bound states even when any two-body subsystems can not bound. An outstanding example is the Efimov states for certain three-body systems with resonant $s$-wave interactions in three dimensions. These Efimov states obey a universal exponential scaling that the ratio between the binding energies of successive Efimov states is a universal number. Recently a field-theoretic calculation predicted a new kind of universal three-body bound states for three identical fermions with resonant $p$-wave interactions in two dimensions. These states were called ``super-Efimov'' states due to their binding energies $E_n=E_*\exp(-2 e^{\pi n/s_0+\theta})$ obeying an even more dramatic double exponential scaling. The scaling $s_0=4/3$ was found to be universal while $E_*$ and $\theta$ are the three-body parameters. Here we use the hyperspherical formalism and show that the ``super-Efimov'' states originate from an emergent effective potential $-1/4\rho^2-(s_0^2+1/4)/\rho^2\ln^2\left(\rho\right)$ at large hyperradius $\rho$. Moreover, our numerical calculation indicates that the three-body parameters $E_*$ and $\theta$ are also universal for pairwise interparticle potentials with a van der Waals tail. [Preview Abstract] |
Tuesday, March 3, 2015 12:51PM - 1:03PM |
G35.00009: Three-body scattering hypervolume for bosons with two-body repulsive Gaussian potentials Shangguo Zhu, Shina Tan It has been known that the three-boson low energy effective interaction influences the dynamic and the static properties of many bosons, including the ground state energy of a dilute Bose-Einstein condensate. The three-body scattering hypervolume, which is a three-body analogue of the two-body scattering length, characterizes this effective interaction. For bosons with two-body repulsive Gaussian potentials, we determine the scattering hypervolume by solving the three-body Schr\"{o}dinger equation numerically, and matching the solution with the asymptotic expansions for the wave function at large hyperradii. [Preview Abstract] |
Tuesday, March 3, 2015 1:03PM - 1:15PM |
G35.00010: Dynamically decoupled three-body interactions with applications to interaction-based quantum metrology Khan W. Mahmud, Eite Tiesinga, Philip R. Johnson We propose a stroboscopic method to dynamically decouple the effects of two-body atom-atom interactions for ultracold atoms, and realize a system dominated by elastic three-body interactions. Using this method, we show that it is possible to achieve the optimal scaling behavior predicted for interaction-based quantum metrology with three-body interactions. Specifically, we show that for ultracold atoms quenched in an optical lattice, we can measure the three-body interaction strength with a precision proportional to ${\bar n}^{-5/2}$ using homodyne quadrature interferometry, and ${\bar n}^{-7/4}$ using conventional collapse-and-revival techniques, where ${\bar n}$ is the mean number of atoms per lattice site. Both precision scalings surpass the nonlinear scaling of ${\bar n}^{-3/2}$, the best so far achieved or proposed with a physical system. Our method of achieving a decoupled three-body interacting system may also have applications in the creation of exotic three-body states and phases. [Preview Abstract] |
Tuesday, March 3, 2015 1:15PM - 1:27PM |
G35.00011: Few Body Physics in Synthetic Dimensions with SU(N) Interactions Sudeep K. Ghosh, Umesh K. Yadav, Vijay B. Shenoy Cold atomic systems with SU(N) symmetric interactions have been of recent experimental and theoretical interest. Motivated by this, we study few body physics in such systems which also realize synthetic dimensions (Celi et al., PRL 112, 043001) within the cold atom setting by coupling the atomic hyperfine states via light. Choosing the light appropriately also provides ability to control magnetic flux in the plaquettes of the synthetic lattice. Using a combination of exact diagonalization and analytical methods, we uncover the novel physics that emerges in the interplay of non-local interactions in synthetic dimensions and the magnetic flux. Attractive SU(N) interactions, in absence of flux, obtains a sequence of multi-particle ``baryonic'' bound states. We show how the presence of flux stabilizes a different sequence of baryonic states, presenting a detailed few body phase diagram. We also discuss consequences of our findings to the many body setting, pointing out the novel phases that can be realized in these systems. These results will be of interest to both experimentalists (suggesting systems with novel physics), as well as theorists for exploring the novel phases realized. [Preview Abstract] |
Tuesday, March 3, 2015 1:27PM - 1:39PM |
G35.00012: A microwave trap for sympathetic cooling of polar molecules Devin Dunseith, Stefan Truppe, Richard Hendricks, Ben Sauer, Edward Hinds, Michael Tarbutt We have been developing techniques to cool molecules into the microkelvin regime. One method is to use sympathetic cooling, using ultracold atoms as a refrigerant to cool molecules. Previous work has suggested that atoms and molecules can be trapped in the antinode of a Fabry-P\'{e}rot microwave cavity. We couple microwave power into this cavity from a rectangular waveguide via a small hole in one mirror. We have developed an analytical model that helps us understand this coupling, and gives us an idea of how the size of the hole affects the cavity's coupling and finesse. We carried out finite--difference time--domain simulations and performed experiments on a prototype cavity to verify this model. We have now designed and built this trap for operation under ultra high vacuum, with the ability to cool the mirrors to 77 K and couple in up to 2 kW of microwave power. This will allow us to trap molecules with a moderate dipole moment at temperatures of hundreds of millikelvin, as well as atoms at a few millikelvin. We will present our work in creating and understanding the microwave trap, as well as our first results demonstrating trapping of lithium atoms in the microwave trap. [Preview Abstract] |
Tuesday, March 3, 2015 1:39PM - 1:51PM |
G35.00013: Hybrid Decelerator for Cold Molecular Beams Igor Lyuksyutov We shall discuss design, simulation and operation of the hybrid decelerator to produce cold molecules. Hybrid decelerator is a combination of the counter rotating source of slow molecular beam with the single stage magnetic decelerator. We operate counter rotating source which provide intense beam of molecules/atoms with the speed smaller than 50m/s. This beam can be a source for the single stage magnetic decelerator. For example, by decreasing the molecular oxygen speed with mechanical decelerator down to 50 m/s, one can use a single stage magnetic decelerator with a maximum current less than 360 A, to decrease the speed of oxygen molecules to about 2m/s. Thus, the use of the magnetic stage in hybrid magneto-mechanical decelerator, can provide slow molecular beams with high intensity. [Preview Abstract] |
Tuesday, March 3, 2015 1:51PM - 2:03PM |
G35.00014: Ultracold nonreactive molecules in an optical lattice Andris Docaj, Michael L. Wall, Kaden R.A. Hazzard Nonreactive (NR) ultracold molecules in optical lattices are free from the two-body losses that occur in chemically reactive molecules, opening up new possibilities for quantum science. Despite the absence of chemical reactions, NR molecules scatter in extremely complex ways -- not captured by a delta function pseudopotential -- due to the enormous number of rotational and vibrational states. We calculate the bound state energies of two NR molecules confined to a single site of an optical lattice, as a first step towards deriving an effective lattice model that can describe many molecules in a lattice. To describe the short-range collisional properties, which are presently experimentally unknown, we employ random matrix theory. However, our formalism is capable of handling arbitrary short-range collisional physics. [Preview Abstract] |
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