Bulletin of the American Physical Society
49th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
Volume 63, Number 5
Monday–Friday, May 28–June 1 2018; Ft. Lauderdale, Florida
Session V03: Bose-Einstein Condensates |
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Chair: Robert Smith, University of Oxford Room: Grand B |
Friday, June 1, 2018 10:30AM - 10:42AM |
V03.00001: Thermodynamics and Structural Transition of Binary Fermi-Bose Mixtures of Ultracold Atoms Tom Kim, Chih-Chun Chien A mixture of spin-polarized fermionic and repulsive bosonic ultracold atoms can go through phase separation if the boson-fermion interaction is sufficiently large. By evaluating the grand partition function using techniques from quantum field theory, we obtain the thermodynamic free energies and its associated quantities in a broad range of temperatures and interaction strength. Stability of a mixture can be inferred from the free energy as the parameters are changed. For a uniform box potential, strong interspecies repulsion separates the bosonic rich and fermionic rich regions, and the thermodynamic quantities of each component can be systematically determined. We map out the full phase diagram of mixtures in a uniform box potential. In the presence of harmonic trap, the density is not uniform. By using the local density approximation, we found several different structures, such as partially mixed regions or fully separated regions, depending on the densities and interactions. We consider realistic parameters from $^6$Li and $^7$Li mixtures and $^6$Li and $^{41}$K mixtures. [Preview Abstract] |
Friday, June 1, 2018 10:42AM - 10:54AM |
V03.00002: Interplay of Coherent and Dissipative Dynamics in Condensates of Light Milan Radonjic, Wassilij Kopylov, Antun Balaz, Axel Pelster Based on the Lindblad master equation approach we obtain a detailed microscopic model of photons in a dye-filled cavity, which features condensation of light. To this end we generalise a recent non-equilibrium approach of Kirton and Keeling such that the dye-mediated contribution to the photon-photon interaction in the light condensate is accessible due to an interplay of coherent and dissipative dynamics. We describe the steady-state properties of the system by analysing the resulting equations of motion of both photonic and matter degrees of freedom. In particular, we discuss the existence of two limiting cases for steady states: photon Bose-Einstein condensate and laser-like. In the former case, we determine the corresponding dimensionless photon- photon interaction strength by relying on realistic experimental data and find a good agreement with previous theoretical estimates. Furthermore, we investigate how the dimensionless interaction strength depends on the respective system parameters. [Preview Abstract] |
Friday, June 1, 2018 10:54AM - 11:06AM |
V03.00003: Interference pattern of colliding composite-boson condensates Aurelia Chenu, Shiue-Yuan Shiau, Monique Combescot All particles consisting of an even number of fermions are boson-like, which bears a strong consequence: they must undergo Bose-Einstein condensation. We predict that, compared to elementary bosons, the interference pattern of two colliding BEC made of atomic dimers must have additional high frequency modes. These new modes being many-body in essence, previous experiments performed with rather dilute condensates only showed interferences ruled by the BECs' momentum difference, a result obtained taking atoms as elementary bosons. The higher frequency modes we predict result from fermion exchanges between condensates and thus constitute a striking signature of the dimer composite nature. We analytically derive the spatial correlation functions and use Shiva diagrams, specific to coboson many-body effects, to identify the physical origin of these modes and determine their experimental observation, using optical lattices. A dimer granularity appears because of Pauli blocking. We anticipate cold-atom systems to provide a novel, fully controllable playground to investigate further the unique many-body effects that result from dimensionless fermion exchanges. Recent optical lattices already reach densities high enough for these to be observable, including the signature predicted here. [Preview Abstract] |
Friday, June 1, 2018 11:06AM - 11:18AM |
V03.00004: Three-body contact dynamics in quenched unitary Bose gases Victor Colussi, John Corson, Jose D'Incao We study the dynamical evolution of the three-body contact in the Bose gas after a quench to the unitary regime. The three-body contact is central to a set of universal relations underlying the many-body theory of the unitary Bose gas [1,2]. We extract the three-body contact by studying three-body correlations at short-distances and times after the quench through a simple model based on analytic solutions of the three-body problem. Our results demonstrate that the three-body contact grows slowly compared to the two-body contact, exhibits coherent oscillations at the frequency of Efimov trimers, and violates the continuous scaling invariance of unitary bosonic systems via the appearance of log-periodic modulation of three-body correlations. [1] E. Braaten, D. Kang, and L. Platter, Phys. Rev. Lett., \textbf{106}, 153005 (2011). [2] F. Werner and Y. Castin, Phys. Rev. A, \textbf{86}, 053633 (2012). [Preview Abstract] |
Friday, June 1, 2018 11:18AM - 11:30AM |
V03.00005: Collective Frequencies of Trapped Photon Bose-Einstein Condensate Enrico Stein, Axel Pelster In a photon Bose-Einstein condensate the main contribution to the effective photon-photon interaction is due to a thermooptic effect. In order to describe this effect at a mean-field level, we use an open- dissipative SchrÃ¶dinger equation coupled to a diffusion equation for the temperature of the dye solution. With this we calculate analytically the lowest-lying collective frequencies and damping rates via a linear stability analysis for a harmonically trapped photon BEC. Since it is not possible to investigate its dynamical properties within a variational approach by using an action, we work out an approximation which is based on determining the equations of motion for the lower moments for Gaussian shaped condensate wave function and temperature distri- bution. As a result of the photon-temperature coupling the collective frequencies and damping rates turn out to depend on the diffusive properties of the dye solution. In particular, we examine whether the Kohn theorem is valid, i.e. whether the dipole-mode frequency is the same as the trap frequency. [Preview Abstract] |
Friday, June 1, 2018 11:30AM - 11:42AM |
V03.00006: Spin dynamics of individual neutral impurities coupled to a Bose-Einstein condensate Daniel Adam, Felix Schmidt, Daniel Mayer, Quentin Bouton, Tobias Lausch, Artur Widera Individual spins immersed into a superfluid form a paradigm of quantum physics. It lies at the heart of many models exploiting the quantum nature of individual spin to understand quantum phenomena or to open novel routes to local probing and engineering of quantum many-body systems. We report on the controlled immersion of individual localized neutral Caesium (Cs) atoms having total spin $F=3$ into a Rubidium Bose-Einstein condensate (BEC) with total spin $F=1$. We observe inelastic spin exchange as well as coherent dynamics of the Cs impurity's quasi-spins interacting with the BEC with high position and time resolution. Our work paves the way for local quantum probing of superfluids, and thus might shed light on the local state of nonequilibrium or correlated quantum many-body systems. [Preview Abstract] |
Friday, June 1, 2018 11:42AM - 11:54AM |
V03.00007: Evolution of the Momentum Distribution of a Bose Gas Quenched to Unitarity Christoph Eigen, Jake Glidden, Raphael Lopes, Eric Cornell, Zoran Hadzibabic, Robert Smith We study the momentum distribution dynamics of a thermal homogeneous $^{39}$K Bose gas quenched to unitarity, where the scattering length diverges. We observe a clear separation in the timescales for the `fast' dynamics due to the change in coherent interactions and the `slow' dynamics due to inelastic three-body loss. Focusing on the short-time dynamics, we find that the redistribution of particles occurs from low to high momentum states with an intermediate momentum shell where the population remains essentially unchanged. By taking measurements across a broad range of different initial atom numbers and temperatures we elucidate universal scaling laws that describe these redistribution dynamics. [Preview Abstract] |
Friday, June 1, 2018 11:54AM - 12:06PM |
V03.00008: Frequency Modulation of Ultracold Atoms by an Oscillating Barrier Andrew Pyle, Drew Rotunno, Shuangli Du, Seth Aubin We present progress on an experiment to study 1D quantum mechanical scattering by an amplitude-modulated barrier. Classically, the oscillating barrier imparts or subtracts kinetic energy in a continuous manner from the scattered atoms. The quantum mechanical energy spectrum of the scattered atoms shows that kinetic energy is added or subtracted in discrete amounts, and thus resembles a comb with a tooth spacing of $\hbar \omega $ where $\omega $ is the oscillation frequency of the barrier. We present an atom chip-based experimental system to study the scattering dynamics with Bose-Einstein condensates (BEC) of $^{\mathrm{87}}$Rb. The experiment operates by releasing a BEC from a magnetic chip trap and directing it horizontally towards a tightly focused laser beam that serves as an oscillating barrier. A magnetic field gradient is used to control the vertical motion of the BEC. This method can be used to study the resulting momentum distributions with a BEC in the presence of no or weak interactions. This experiment represents a first step toward implementing a quantum pump for ultracold atoms based on two such barriers modulated out of phase with one another. [Preview Abstract] |
Friday, June 1, 2018 12:06PM - 12:18PM |
V03.00009: Tunneling Times and Studying the Effects of Dissipation David Spierings, Ramon Ramos, Isabelle Racicot, Bryce Wu, Aephraim Steinberg How much time does a tunneling particle spend in the barrier region?~ An answer to this question may be defined by considering a ``weak measurement'' in the sense of Aharonov, Albert, and Vaidman.~ A Larmor clock, which uses a spin degree of freedom to keep time, can implement such a measurement experimentally [1]. ~Here, we report the status of our experiment on measuring times for Bose-condensed Rubidium~atoms tunneling through a 1-micron optical barrier [2]. ~We also consider probing the quantum/classical transition by studying what happens when the Larmor measurement is made "strong" and/or under the influence of engineered dissipation [3]. [1] Steinberg, A. M. (1998). Time and history in quantum tunneling. \textit{Superlattices and Microstructures}, \textit{23}(3--4), 823--832. \underline {http://doi.org/10.1006/spmi.1997.0543} [2] Potnis, S., Ramos, R., Maeda, K., Carr, L. D., {\&} Steinberg, A. M. (2017). Interaction-Assisted Quantum Tunneling of a Bose-Einstein Condensate out of a Single Trapping Well. \textit{Physical Review Letters}, \textit{118}(6), 1--5. \underline {http://doi.org/10.1103/PhysRevLett.118.060402} [3] Steinberg, A. M. (1999). On energy transfer by detection of a tunneling atom. Korean Physical Society 35 (3), 122. (\underline {http://arxiv.org/abs/quant-ph/9904098}) [Preview Abstract] |
Friday, June 1, 2018 12:18PM - 12:30PM |
V03.00010: Hyperspherical-LOCV Approximation to Resonant BEC Michelle Wynne Sze, Andrew Sykes, Doerte Blume, John Bohn We study the ground state properties of a system of harmonically trapped bosons interacting with two-body contact interactions, from small to large scattering lengths. This is accomplished in a hyperspherical coordinate system that is flexible enough to describe both the overall scale of the gas and two-body correlations. By adapting the lowest-order constrained variational (LOCV) method, we are able to semi-quantitatively attain Bose-Einstein condensate ground state energies even for gases with infinite scattering length. In the large particle number limit, our method provides analytical estimates for the energy per particle $E_0/N \approx 2.5 N^{1/3} \hbar \omega$ and two-body contact $C_2/N \approx 16 N^{1/6}\sqrt{m\omega/\hbar}$ for a Bose gas on resonance. [Preview Abstract] |
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