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 J7: Bose-Einstein Condensates |
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Chair: David Weld, University of California, Santa Barbara Room: 313 |
Wednesday, June 7, 2017 2:00PM - 2:12PM |
J7.00001: Measurement of quantum depletion in a homogeneous Bose-Einstein condensate Raphael Lopes, Christoph Eigen, Nir Navon, Robert Smith, Zoran Hadzibabic Using momentum selective Bragg scattering we measure the condensed fraction of a strongly interacting homogeneous BEC. When adiabatically increasing the scattering length, we see that the condensed fraction decreases linearly with $\sqrt{na^3}$ (where $n$ is the density), in excellent agreement with the Bogoliubov theory of quantum depletion. We also show the reversibility of this process by adiabatically reducing the scattering length. [Preview Abstract] |
Wednesday, June 7, 2017 2:12PM - 2:24PM |
J7.00002: Bosonic Particle-Correlated States: A Nonperturbative Treatment Beyond Mean Field Zhang Jiang, Alexandre Tacla, Carlton Caves We consider a natural generalization of the product ansatz for Bose-Einstein condensates; the particle-correlated state of $N=l\times n$ identical particles is derived by symmetrizing the $n$-fold product of an $l$-particle quantum state. Quantum correlations of the $l$-particle state ``spread out" to any subset of the $N$ particles by symmetrization. The particle-correlated states can be simulated efficiently for large $N$, because their parameter spaces, which depend on $l$, do not grow with $n$. We pay special attention to the pure-state case for $l=2$, where the many-body state is constructed from a two-particle pure state. These paired wave functions were introduced by Leggett [Rev. Mod. Phys. $\mathbf{73}$, 307 (2001)] as a particle-number-conserving version of the Bogoliubov approximation. For large $N$, we derive few-particle reduced density matrices (correlation functions) for these wave functions. To test the efficacy of our theory, we solve the two-site Bose-Hubbard model by minimizing the energy using the two-particle reduced density matrices that we derived analytically. We find that the relative errors of the ground state energy are within $10^{-5}$ for $N=1000$ particles over the entire range from a single condensate to a Mott insulator. [Preview Abstract] |
Wednesday, June 7, 2017 2:24PM - 2:36PM |
J7.00003: Bloch-Siegert shift in an interacting Bose-Einstein condensate Jinyi Zhang, Christoph Eigen, Raphael Lopes, Sam Garratt, David Rousso, Robert P. Smith, Zoran Hadzibabic, Nir Navon The Bloch-Siegert shift $\cite{Bloch}$ (BSS) is a paradigmatic frequency shift that arises from the nonlinear response of a two-level system (TLS) subjected to strong driving fields. When a TLS is driven by a linearly polarized field, the co-rotating-wave component leads to the famous Rabi oscillations. By contrast the co-rotating-wave component, whose role is usually neglected in a weak driving, leads to a frequency shift of the TLS resonance frequency. This phenomenon is encountered in various areas, from quantum optics to nuclear magnetic resonance.\par Here, we investigate the BSS in a box-trapped ${}^{87}\!Rb$ Bose-Einstein condensate (BEC) driven by a strong oscillating magnetic field gradient $\cite{Nir}$. By tuning the chemical potential of the gas, we investigate how the BSS evolves from the ideal shift of the two lowest energy levels of a single particle in a box to the unexplored shift of long-wavelength collective excitations of the interacting BEC. \begin{thebibliography} \small \bibitem{Bloch} F. Bloch and A. Siegert, Phys. Rev. 57, 522 (1940). \bibitem{Nir} N. Navon, A. L. Gaunt, R. P. Smith and Z. Hadzibabic, Nature 539, 72 (2016). \end{thebibliography} [Preview Abstract] |
Wednesday, June 7, 2017 2:36PM - 2:48PM |
J7.00004: Creating the first Bose-Einstein Condensate in Space M. Lachmann, S. Seidel, D. Becker, H. Ahlers, T. Wendrich, J. Grosse, H. Müntinga, B. Weps, A. Dinkelaker, V. Schkolnik, O. Hellmig, A. Wenzlawski, W. Herr, N. Gaaloul, E. Rasel, W. Ertmer On 23$^{\mathrm{rd}}$ of January 2017 the first Bose-Einstein Condensate (BEC) in Space was created onboard the sounding rocket mission MAIUS-1. The successful launch marks a major advancement in the effort of performing matter wave interferometry with BECs on space vehicles. Its high BEC-flux enables more than 100 experiments during flight, characterizing the creation of BECs in space, their free evolution, state preparation, and the creation of cold atoms in highly dynamic environments. MAIUS-1 opens a new path towards space borne inertial sensing employing interferometers with high accuracy and sensitivity. Two follow-up missions will investigate dual-species interferometry. Recently several missions were proposed ranging from tests of the universality of free fall to gravimetry. Due to their small initial size and low expansion rates BECs are the ideal source for such an interferometric measurement. The findings of the mission will contribute to the NASA CAL project and BECCAL (NASA and DLR). DLR under grant 50WP1435 [Preview Abstract] |
Wednesday, June 7, 2017 2:48PM - 3:00PM |
J7.00005: Efimov Trimer Production in a Resonantly Interacting BEC Xin Xie, Catherine Klauss, Carlos Abadia, Jose D'incao, Zoran Hadzibabic, Deborah Jin, Eric Cornell Ultracold quantum gases with resonant interactions have been in focus for decades as an ideal and tunable model of many-body physics. Fermi gases have been widely studied owing to its direct relation to realistic materials. Resonantely interacting Bose gases, however, were first observed only a couple of years ago due to its short lifetime caused by three-body recombination. Such three-body interaction is an intriguing feature of Efimov physics which is absent in the Fermionic counterpart. We previously observed a relatively stable degenerate Bose gas by quenching to unitarity. This state equilibrates many times faster than the gas's lifetime. In this work, we did a closer investigation into this quasi-equilibrium state by projecting it onto weakly interacting regimes and probing it therein. We discovered dramatic signatures of Efimov trimers by measuring their one-body decay time that agrees with theoretical calculations. We propose that such formation of trimers is related to the finite overlap between trimer wavefunctions and short-range correlations in the quenched state. And the study of molecules in their well-characterized states provide a unique pathway to understand the two-body and three-body correlations in resonantly interacting BEC. [Preview Abstract] |
Wednesday, June 7, 2017 3:00PM - 3:12PM |
J7.00006: Density--density correlations and Hawking radiation in ultracold gases Yi-Hsieh Wang, Ted Jacobson, Mark Edwards, Charle W. Clark We simulate recent experiments on Bose-condensed gases in which the spontaneous production of analog Hawking radiation was inferred from the observation of density--density correlations. Even when the gas sample is a pure Bose-Einstein condensate, we find that such correlations are present in realistic simulations. This is due to the random shot-to-shot variation in the number of atoms in the sample. This simple effect of ``sample inhomogeneity" is comparable to that of quantum fluctuations, and is comparable to what is observed in experiments. [Preview Abstract] |
Wednesday, June 7, 2017 3:12PM - 3:24PM |
J7.00007: Quantitative many-body theory of unitarity BECs Mackillo Kira Perturbative approaches, such as the Gross-Pitaevskii equation, can successfully explain weak interactions in BECs, while they become questionable at unitarity where the scattering length diverges. The first unitary BEC experiment\footnote{P.~Makotyn, {\it et al.}, Nat.~Phys.~{\bf 10},~116--119 (2014).} demonstrated that a surprisingly large BEC fraction survived a quench from weak to unitary interactions. I will show that introducing an excitation picture\footnote{M.~Kira, Ann.~Phys.~{\bf 351}, 200--249 (2014).} identifies how a quench creates noncondensed atoms in a strict sequential order\footnote{M.~Kira, Ann.~Phys.~{\bf 356}, 185--243 (2015).} where large atom clusters only emerge from existing smaller ones. This observation yields an efficient nonperturbative many-body description of unitary BECs, based on a cluster-expansion approach developed originally for semiconductor quantum optics\footnote{M.Kira \& S.W.Koch, {\it Semiconductor Quantum Optics}, (Cambridge Univ.~Press, 2012).}. I will discuss how this method quantitatively explains\footnote{M.Kira, Nat.~Commun.~\textbf{6}, 6624 (2015).} the first unitarity BEC measurement, and how it can be extended to explore, e.g., Efimov physics, universality, and entanglement in one or many strongly interacting BECs. [Preview Abstract] |
Wednesday, June 7, 2017 3:24PM - 3:36PM |
J7.00008: Wave function based treatment of the unitary Bose gas Michelle Wynne Sze, John Corson, Jose d' Incao, John Bohn Understanding many body quantum systems remains a challenging task as recent experiments on ultracold gases extend to unitary regime. We study a system of $N$ identical harmonically-trapped bosons interacting via a contact interaction by starting from a few body system, and employing the adiabatic hyperspherical method and Fadeev decomposition approach. In our formulation, we determine the hyperangular energy eigenstates (and consequently the total energy of the system) from the Bethe-Peierl's boundary condition applied to the symmetrized wavefunction and where the only relevant parameters are the scattering length and the average size of the system given by the hyperradius $R$. We reproduce the well-understood stationary properties and characteristics of weakly to strongly interacting three-body systems. Results from these are exploited for the study of larger $N>3$ and the dynamics of three-body systems. [Preview Abstract] |
Wednesday, June 7, 2017 3:36PM - 3:48PM |
J7.00009: Universal Loss Dynamics of a Degenerate Homogeneous Unitary Bose Gas Christoph Eigen, Jake Glidden, Raphael Lopes, Jinyi Zhang, Nir Navon, Zoran Hadzibabic, Robert Smith We study the loss dynamics of a degenerate $^{39}$K Bose gas confined in an optical box trap. Starting with a quasi-pure Bose-Einstein condensate in the Thomas-Fermi regime, where the density $n$ is uniform, we quench the scattering length $a$ to the unitary regime, where $a$ diverges. Observing the cloud after a variable hold time at unitarity directly reveals a loss rate which is dictated solely by the density of the cloud and scales as $n^{\frac{2}{3}}$. This is in stark contrast to measurements performed away from unitarity, where the more conventional $n^{2}$ scaling is observed. Our measurements also provide insight into the time evolution of the momentum distribution at unitarity. [Preview Abstract] |
Wednesday, June 7, 2017 3:48PM - 4:00PM |
J7.00010: Hollow shell geometry and topological change of spherical Bose-Einstein condensates Karmela Padavic, Kuei Sun, Frances Yang, Courtney Lannert, Smitha Vishveshwara We present our study [\underline {arXiv:1612.05809}] and recent progress on a spherical BEC undergoing a topological change from a filled sphere to a novel hollow shell geometry. Motivated by the upcoming realization of these hollow systems by NASA's Cold Atom Laboratory, we analyze their equilibrium properties and collective mode (CM) structure. We show that distinctive non-monotonic features in the CM spectrum of a spherical BEC indicate its deformation from a filled to a hollow geometry and the emergence of an inner boundary. This topological change produces the most drastic effect for high angular momentum CMs as they correspond to surface modes localized to condensate boundaries and undergo a redistribution of nodes once an additional boundary is present. Additionally, our numerical simulations show how the CM features can be probed in typical sudden-quench experiments. Finally, we go beyond the micro-gravity regime, discussing how the equilibrium and CM properties are modified as gravity breaks the spherical symmetry. [Preview Abstract] |
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