Bulletin of the American Physical Society
51st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 65, Number 4
Monday–Friday, June 1–5, 2020; Portland, Oregon
Session P09: Topological ExcitationsLive
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Chair: Robert Lewis-Swan, JILA Room: Portland 256 |
Thursday, June 4, 2020 2:00PM - 2:12PM Live |
P09.00001: Deterministic Prediction/Validation of Tilted Optical Vortex Trajectories by Treating Light as a Two-Dimensional, Compressible Medium Mark Lusk, Jasmine Andersen, Andrew Voitiv, Mark Siemens We quantify the motion of optical vortices by treating light as a two-dimensional, compressible medium. The field of an optical vortex can be unwound with the background field used to construct two vortex velocity components. One is proportional to the gradient of the optical phase and is parallel to the local streamlines of the background velocity field. The other, though, is a functional of the local intensity of the optical field. This second contribution is particularly important for predicting trajectories associated with the nucleation and annihilation of vortex doublets, where vortices can be severely tilted. The approach is implemented for settings with analytic solutions for both the field and the trajectories. The predicted vortex velocities are shown to be tangent to the analytic trajectory, a validation of the theory and methodology. Our experimental implementation gives comparable vortex trajectories. The role of optical fluid compressibility has important implications for understanding and controlling the motion of optical vortices. Two-dimensional Bose-Einstein condensates should exhibit vortex tilt as well. If so, accounting for it in the same way will allow their vortex paths to be anticipated. [Preview Abstract] |
Thursday, June 4, 2020 2:12PM - 2:24PM Live |
P09.00002: Geometric squeezing into the lowest Landau Level by rotating a Bose-Einstein Condensate (BEC) Airlia Shaffer, Richard Fletcher, Cedric Wilson, Parth Patel, Zhenjie Yan, Valentin Crepel, Biswaroop Mukherjee, Martin Zwierlein A key feature of the physics of charged particles in a magnetic field, or equivalently neutral particles under rotation, is that translations along orthogonal spatial directions do not commute. By rotating a BEC, we observe the dynamics of a single wavefunction living in this geometry and use the noncommutativity to squeeze in real space. We demonstrate the incompressibility of guiding center flow and squeeze the guiding center distribution by more than 7dB below the standard quantum limit. This squeezing procedure dynamically creates a BEC in the lowest Landau level, signaled by the density distribution changing from Thomas-Fermi to Gaussian as well as the cloud width saturating to the size of cyclotron orbit's zero-point motion. The condensate attains an angular momentum of more than 1000 $\hbar $ per particle and an interparticle spacing approaching the size of the cyclotron orbits, offering a new route towards bosonic quantum Hall states. [Preview Abstract] |
Thursday, June 4, 2020 2:24PM - 2:36PM Live |
P09.00003: Controlled persistent current transport between toroidal quantum gases Thomas Bland, Artem Oliinyk, Oksana Chelpanova, Igor Yatsuta, Charles Henry, Luigi Amico, Leong Chuan Kwek, Mark Edwards, Nick Proukakis, Alexander Yakimenko Realizing transport of quantized vorticity between ring-shaped atomic Bose-Einstein condensates could be a key step in diverse cold atom quantum technologies and atomtronic devices. In this work we present recent results on the deterministic transfer of persistent current between co-planar rings of cold atoms, creating a prototype atomtronic switch through a tunable weak link at the common interface of two density-coupled rings. We explicitly demonstrate such transfer with the presence of both rotation and linear translation, within the context of pure mean-field simulations (Gross-Pitaevskii equation) and examine the sensitivity of this process to finite-temperature fluctuations (by self-consistently coupling the dissipative Gross-Pitaevskii equation to a quantum Boltzmann equation for the thermal cloud, known as the Zaremba-Nikuni-Griffin method). These investigations open perspectives for the development of a novel type of quantum sensor based on angular momentum transfer in atomtronic circuits. [Preview Abstract] |
Thursday, June 4, 2020 2:36PM - 2:48PM Live |
P09.00004: Quadrupole Raman transitions driven by optical vortex beams in ultracold atomic clouds Joseph D. Murphree, Maitreyi Jayaseelan, Zekai Chen, Elisha Haber, Nicholas P. Bigelow Recent experiments in trapped ions demonstrate that a circularly polarized Laguerre--Gaussian (LG) beam carrying orbital angular momentum (OAM) transfers both components of its angular momentum---polarization and OAM---to the valence electron of the ion via a quadrupole transition. This displays a richer interaction between the angular momenta of the atom and the field compared to dipole transitions, where the polarization couples solely to the electron's angular momentum and the OAM couples to the atom's center of mass motion. It also promises the ability to control electronic transitions by manipulating the spatial distributions of the intensity and phase of the applied field. Two-photon Raman processes composed of two such quadrupole transitions will also display these novel features, and can be configured to coherently transfer the electron between states in the ground state manifold, allowing quadrupole transitions to be explored in low energy quantum systems. We examine the effects of these quadrupole Raman transitions driven by LG beams on an ultracold atomic cloud. We discuss the experimental parameters necessary for realizing the transitions in the lab, considering specifically the $5\,^2\textrm{S}_{1/2}\rightarrow4\,^2\textrm{D}_{1/2}$ transition in rubidium-87. [Preview Abstract] |
Thursday, June 4, 2020 2:48PM - 3:00PM Live |
P09.00005: Magneto-Roton Instability in a Rotating Bose-Einstein Condensate Biswaroop Mukherjee, Airlia Shaffer, Cedric Wilson, Parth B. Patel, Zhenjie Yan, Bola Malek, Valentin Cr\'{e}pel, Richard Fletcher, Martin W. Zwierlein Magneto-rotons are elementary excitations at finite momentum that appear in gases of interacting charged particles placed under a strong magnetic field. With rotation as an analog to a magnetic field, the excitation spectrum of a rotating weakly-interacting Bose-Einstein condensate (BEC) in an anisotropic confinement potential is also predicted to exhibit a roton feature. We observe the dynamical instability of a BEC under rotation, and witness a spontaneous translational symmetry breaking in the density profile of the BEC. We identify this instability with the population of an interaction-driven magneto-roton mode, and measure the variation of the lengthscales and growth rates of the resulting roton crystal with interactions. These results indicate the emergence of a roton with a rotational sense, and shed light on the development of a magneto-roton in a superfluid. [Preview Abstract] |
Thursday, June 4, 2020 3:00PM - 3:12PM Live |
P09.00006: Phonon Fluctuations in a Bose-Einstein Condensate Subject to Repeated Weak Measurements Emine Altuntas, Shangjie Guo, Hilary Hurst, Yuchen Yue, Francisco Salces-Carcoba, Christopher Billington, Ian B. Spielman Weak measurements are minimally destructive measurement techniques that present new opportunities for understanding the system-reservoir dynamics of many-body systems. Weak measurements yield a controlled reservoir and consequently allow time-resolved study of the system evolution.~We experimentally study the phonon fluctuations that result from the quantum backaction induced by repeated weak measurements in quasi-one dimensional Bose-Einstein condensates (BECs). We use partial transfer absorption imaging (PTAI) technique to obtain minimally destructive and multiple successive \textit{in situ} images of the same BEC.~We describe the reciprocal space analysis of the density profiles and present the resultant space-time separated density-density correlation functions.~Further we discuss feedback control protocols for future applications of Hamiltonian engineering using weak measurements and feedback.~ [Preview Abstract] |
Thursday, June 4, 2020 3:12PM - 3:24PM Live |
P09.00007: Observation of hypersonic flow dynamics with Bose-Einstein condensates Maren Mossman, Peter Engels Ultracold quantum gases are intriguing systems that exist in highly tunable environments. This tunability makes quantum gases powerful candidates for probing fluid dynamics, where much of the past work has dealt with flow patterns and excitations emerging at or below the speed of sound in the system, i.e. in the near-supersonic or subsonic regime. Here, we conduct experiments with Bose-Einstein condensates that investigate fast-flow dynamics in the hypersonic regime. For example, we observe the emergence of interesting shock-like features when a hypersonic flow of atoms passes a repulsive barrier. We characterize these features and their parameter dependence, such as their dependence on the shape and angle of the barrier. Applications and the current status of this work, along with future directions, shall be discussed. [Preview Abstract] |
Thursday, June 4, 2020 3:24PM - 3:36PM On Demand |
P09.00008: Acoustic Models for Atomtronic Circuits Tyler Neely, Guillaume Gauthier, Stuart S. Szigeti, Matthew T. Reeves, Mark Baker, Thomas A. Bell, Halina Rubinsztein-Dunlop, Matthew J. Davis Atomtronics emerged more than 10 years ago as a framework for enhancing and developing applications of cold- atom technology, such as quantum sensors. Similar to what electrical circuit theory provides to electronics, atomtronics requires simple yet quantitative models that describe fundamental circuit elements. Such models should be able to predict the behavior of relatively simple circuit elements, analogous to capacitors, resistors, and inductors. We study a $^{87}$Rb BEC superfluid confined to a highly configurable optical trap that produces a ``dumbbell" atomtronic circuit, with two reservoirs connected by a tunable channel. We first examine the behavior of the circuit in response to a small initial chemical potential bias. We demonstrate experimentally and numerically that an approach based on classical acoustic circuit theory, rather than electrical circuit theory, can quantitatively predict the behavior of the circuit. We also study the responses to larger initial chemical potential biases, and compare these with phase-slip models of dissipation. Our work suggests that empirical models of turbulent dynamics in the system, as have been used in classical acoustics, will be needed to fully understand the behavior of atomtronic circuits in these regime. [Preview Abstract] |
Thursday, June 4, 2020 3:36PM - 3:48PM On Demand |
P09.00009: Subradiance-protected excitation spreading in the generation of collimated photon emission from an atomic array Kyle Ballantine, Janne Ruostekoski We show how an initial localized radiative excitation in a two-dimensional array of cold atoms can be converted into highly-directional coherent emission of light by protecting the spreading of the excitation across the array in a subradiant collective eigenmode with a lifetime orders of magnitude longer than that of an isolated atom. The excitation, which can consist of a single photon, is then released from the protected subradiant eigenmode by controlling the Zeeman level shifts of the atoms. Hence, an original localized excitation which emits in all directions is transferred to a delocalized subradiance-protected excitation, with a probabilistic emission of a photon only along the axis perpendicular to the plane of the atoms. This protected spreading and directional emission could potentially be used to link stages in a quantum information or quantum computing architecture. [Preview Abstract] |
Thursday, June 4, 2020 3:48PM - 4:00PM On Demand |
P09.00010: Non-destructive probing of magnetic excitations in an antiferromagnetic spin-1 Bose-Einstein condensate Xiao Chai, Di Lao, Chandra Raman Spin-1 antiferromagnetic Bose-Einstein condensates (BECs) possess various magnetic excitations, e.g. magnetic solitons which we have recently studied [1]. Those magnetic excitations are uniquely characterized by the time evolution and spatial distribution of their magnetization and the domain walls in the nematicity. However in our previous work, probing of the magnetization evolution is limited by the destructive nature of Stern-Gerlach measurement. Stray magnetic field noise breaks the spin coherence and makes phase measurement, and therefore, characterization of the nematicity, unsuccessful. Here we investigate an experimental protocol to non-destructively obtain both magnetic and nematic information using repeated imaging via microwave excitation to the upper hyperfine level. By actively stabilizing the magnetic field, nematicity measurement is made possible with interferometry methods. Our protocol offers tools for characterizing magnetic excitations in spinor BECs, and eventually for understanding magnetic excitations generated in non-equilibrium processes. [1] Chai, Xiao, et al. "Magnetic solitons in a spin-1 Bose-Einstein condensate." arXiv preprint arXiv:1912.06672 (2019). [Preview Abstract] |
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