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 H9: Long Range Interactions II |
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Chair: Georg Raithel, University of Michigan Room: 315 |
Wednesday, June 7, 2017 10:30AM - 10:42AM |
H9.00001: Strongly dipolar Bose gases Krzysztof Jachymski, Rafal Oldziejewski Strongly dipolar Bose gases can form liquid droplets stabilized by quantum fluctuations. In a theoretical description of this phenomenon, the low-energy scattering amplitude is utilized as an effective potential. We show that for magnetic atoms corrections with respect to the Born approximation should be included in theoretical description. We derive a modified pseudopotential using a realistic interaction model. We then discuss the construction of the effective low-energy Hamiltonian for trapped systems with long-range interactions. Our results are relevant to recent experiments with erbium and dysprosium atoms. [Preview Abstract] |
Wednesday, June 7, 2017 10:42AM - 10:54AM |
H9.00002: Dipolar dark solitons Kazimierz Rzazewski We study dark soliton-like excitations in the BEC dominated by long range dipolar forces. We do it in a one dimensional ring geometry, in a 1D and 3D elongated harmonic trap. We show that these solitons interact at a distance and undergo inelastic collisions. We also show that in the harmonic trap, in contrast with solitons in the contact interacting gas, the oscillation frequency depends on the strength of interaction. We also determine the boundary of stability of these excitations. [Preview Abstract] |
Wednesday, June 7, 2017 10:54AM - 11:06AM |
H9.00003: Engineering Bright Matter-Wave Solitons of Dipolar Condensates Matthew Edmonds, Thomas Bland, Ryan Doran, Nick Parker The ongoing interest in ensembles of ultracold matter possessing significant magnetic dipole moments has lead to new insight into these macroscopic magnetic systems; such as manifestation of droplet phases [1-3]. Here, we analyze the form and interaction of dipolar bright solitons across the full parameter space afforded by dipolar Bose-Einstein condensates, revealing inelastic soliton dynamics. From this, three collisional regimes emerge: free collisions, bound state formation and soliton fusion. We further examine the stability of these states by employing a three-dimensional variational analysis; along with regimes where the dipolar bright soliton is unstable to collapse or expansion, we identify regions of stability which are accessible to current experiments [4]. [1] H. Kadau, M. Schmitt, M. Wenzel, C. Wink, T. Maier, I. F.-Barbut, and T. Pfau, {\it Nature} {\bf 10}, 1038 (2016). [2] I. F.-Barbut, H. Kadau, M. Schmitt, M. Wenzel, and T. Pfau, {\it Phys. Rev. Lett.} {\bf 116}, 215301 (2016). [3] L. Chomaz, S. Baier, D. Petter, M. J. Mark, F. W\"achtler, L. Santos, and F. Ferlaino, {\it Phys. Rev. X} {\bf 6}, 041039 (2016). [4] M. J. Edmonds, T. Bland, R. Doran, and N. G. Parker, arXiv:1610.01022 ({\it New. J. Phys.}, in press) [Preview Abstract] |
Wednesday, June 7, 2017 11:06AM - 11:18AM |
H9.00004: Dipolar lattice bosons in the presence of long-range hopping Chao Zhang, Arghavan Safavi-Naini, Barbara Capogrosso-Sansone We report on numerical results based on quantum Monte Carlo simulations of a system of two-dimensional hard-core lattice bosons in the presence of long-range hopping and long-range two-body interactions resulting from dipole-dipole interactions. This is equivalent to the XXZ model in the presence of dipolar interactions which can be realized by a lattice gas of polar molecules, creating a flexible platform for the study of quantum magnetism. The system features three phases: a superfluid, a supersolid, and a checkerboard solid. Next we mimic the current experimental conditions, that is a lattice of polar molecules away from unit filling, by adding static disorder. Under these conditions we study the localization of particles and the stabilization of a disorder-induced insulating phase. [Preview Abstract] |
Wednesday, June 7, 2017 11:18AM - 11:30AM |
H9.00005: Excitations of dipolar quantum droplets Ryan Wilson, Danny Baillie, P. Blair Blakie A wave of exciting experiments with atomic Dysprosium and Erbium have demonstrated the stabilization of a collapsing dipolar Bose-Einstein condensate into long-lived droplet states, which can exist without the support of an external trapping potential. This stabilization is likely due to the unique effects of beyond mean-field quantum fluctuations in dipolar systems. We study the elementary excitations of these droplets using an appropriately modified Bogoliubov theory, for both trapped and free droplets. Interestingly, these droplets support fully self-localized excitations, the number of which is found to increase with decreasing scattering length. We analyze the properties of these excitations, and discuss their implications for modern experiments with dipolar gases. [Preview Abstract] |
Wednesday, June 7, 2017 11:30AM - 11:42AM |
H9.00006: Manifestations of dipolar collisions in thermal and BEC gases of dysprosium Yijun Tang, Andrew Sykes, Nathaniel Burdick, Dmitry S. Petrov, Benjamin Lev Ultracold and quantum gases of dysprosium provide the opportunity to explore the physics of strongly dipolar gases. In this talk, we report on two recent experiments that highlight this physics. The first is a direct measurement of collisions between two Bose-Einstein condensates with strong dipolar interactions. A collision halo corresponding to the two-body differential scattering cross section is observed. The results demonstrate a novel regime of quantum scattering, relevant to dipolar interactions, in which a large number of angular momentum states become coupled during the collision. We perform Monte-Carlo simulations to provide a detailed comparison between theoretical two-body cross sections and the experimental observations. The second is a measurement of the anisotropic expansion of ultracold bosonic dysprosium gases at temperatures above quantum degeneracy. We develop a theory to express the post-expansion aspect ratio in terms of temperature and microscopic collisional properties by incorporating Hartree-Fock mean-field interactions, hydrodynamic effects, and Bose-enhancement factors. Our results extend the utility of expansion imaging by providing accurate thermometry for dipolar thermal Bose gases. [Preview Abstract] |
Wednesday, June 7, 2017 11:42AM - 11:54AM |
H9.00007: Dilute magnetic droplets of a bosonic erbium quantum fluid. Lauriane Chomaz, Simon Baier, Daniel Petter, Giulia Faraoni, Jan-Hendrik Becher, Rick van Bijnen, Manfred J. Mark, Francesca Ferlaino Due to their large magnetic moment and exotic electronic configuration, atoms of the lanthanide family, such as dysprosium (Dy) and erbium (Er), are an ideal platform for exploring the competition between inter-particle interactions of different origins and behaviors. Recently, a novel phase of dilute droplet has been observed in an ultracold gas of bosonic Dy when changing the ratio of the contact and dipole-dipole interactions and setting the mean-field interactions to slightly attractive. This has been attributed to the distinct, non-vanishing, beyond-mean-field effects in dipolar gases when the mean interaction cancels. Here we report on the investigation of droplet physics in fluids of bosonic Er. By precise control of the scattering length $a$, we quantitatively probe the Bose-Einstein condensate (BEC)-to-droplet phase diagram and the rich underlying dynamics. In a prolate geometry, we observe a crossover from a BEC to a single macro-droplet, prove the stabilizing role of quantum fluctuations and characterize the special dynamical properties of the droplet. In an oblate geometry, we observe the formation of assemblies of tinier droplets arranged in a chain and explore the special state dynamics following a quench of $a$, marked by successive merging and reformation events. [Preview Abstract] |
Wednesday, June 7, 2017 11:54AM - 12:06PM |
H9.00008: Quantum Dynamics in the HMF Model Ryan Plestid, Duncan O'Dell The Hamiltonian Mean Field (HMF) model represents a paradigm in the study of long-range interactions but has never been realized in a lab. Recently Shutz and Morigi (PRL 113) have come close but ultimately fallen short. Their proposal relied on cavity-induced interactions between atoms. If a design using cold atoms is to be successful, an understanding of quantum effects is essential. I will outline the natural quantum generalization of the HMF assuming a BEC by using a generalized Gross-Pitaevskii equation (gGPE). I will show how quantum effects modify features which are well understood in the classical model. More specifically, by working in the semi-classical regime (strong interparticle interactions) we can identify the universal features predicted by catastrophe theory dressed with quantum interference effects. The stationary states of gGPE can be solved exactly and are found to be described by self-consistent Mathieu functions. Finally, I will discuss the connection between the classical description of the dynamics in terms of the Vlassov equation, and the gGPE. [Preview Abstract] |
Wednesday, June 7, 2017 12:06PM - 12:18PM |
H9.00009: Localization of quantum particles with long-range hopping in finite-sized lattices Joshua T Cantin, Tianrui Xu, Roman V Krems Non-interacting particles with long-range hopping are known to be delocalized in disordered systems of infinite size. It is thus natural to assume that such particles can traverse any finite-sized lattice. We show that this is not true. Particles with long-range hopping can localize in lattices of \emph{finite} size, even macroscopically finite. This leads to a rather unusual phenomenon: quantum particles can transverse a disordered lattice of size $10A$, but not a lattice of size $A$. As evidence for this, we demonstrate spatial localization in dynamical calculations at long-times, inverse participation ratio distributions characteristic of localized systems, and log-normal fluctuations of the wavefunction. We map out the phase diagram for a particle with long-range hopping in a 3D lattice as a function of on-site disorder strength and filling fraction. Using scaling arguments, we determine the size-dependence of the localization-diffusion crossover line as a function of the system size, which predicts localization in macroscopically finite systems. [Preview Abstract] |
Wednesday, June 7, 2017 12:18PM - 12:30PM |
H9.00010: Trapping Ions in an optical lattice for quantum simulation Matt Grau, Christoph Fischer, Oliver Wipfli, Jonathan Home Quantum many-body spin Hamiltonians are important tools for describing condensed matter systems, but many such Hamiltonians are difficult to simulate on classical computers. Quantum simulation offers an avenue for overcoming these limitations. Arrays of trapped ions are an attractive platform for quantum simulation due to the high level of control combined with the intrinsic long-range Coulomb interaction that can be used to engineer tunable spin-spin couplings. However, varying lattice geometry is challenging with current trapping techniques. We are developing a new apparatus to trap arrays of ions in optical lattices for the purpose of quantum simulation. This should allow trapping two and three-dimensional crystals with a designed geometry. I will present results of simulations of equilibrium positions and normal modes of such a system, which indicate that in a first design arrays of around 40 ions could be trapped with ion-ion distances of under 10 microns, and also with low residual heating rates due to off-resonant scattering and laser fluctuations. By using Magnesium ions, we expect to be able to cool and image the ions while trapped in a deep optical lattice formed by a high finesse optical cavity. Experimental progress towards these goals will be described. [Preview Abstract] |
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