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 P06: Generation, Detection and Dynamics of Solitons in BoseEinstein CondensatesLive

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Chair: Randy Hulet, Rice University Room: E141142 
Thursday, June 4, 2020 2:00PM  2:12PM Live 
P06.00001: Quench dynamics and Townes soliton formation in twodimensional Bose gases ChengAn Chen, ChenLung Hung Predicting the evolution of manybody systems under attractive interactions is a challenging task, owing to the instability to collapse. Bright solitons are remarkable stationary states, established when the selffocusing effect responsible for collapse is exactly compensated by the wave dispersion. In twodimensional (2D) Bose gases, however, such intricate balance cannot be fulfilled except at a critical norm known as the Townes threshold – only at which matterwave bright solitons can form. By quenching the atomic interaction from repulsive to attractive via a Feshbach resonance \footnote{ChengAn Chen and ChenLung Hung, \textbf{arXiv}:1907.12550 (2019).}, we report the observation of Townes solitons formation through the manifestation of modulational instability that results in the amplification of density wave disturbances and fragmentation of a 2D sample. Our highresolution density measurements in space and time domain reveal detailed information about the formation process, and demonstrate multiple universal behaviors in association with the formation of a stationary state in an attractive manybody system. [Preview Abstract] 
Thursday, June 4, 2020 2:12PM  2:24PM Live 
P06.00002: Formation of bright matterwave breathers D. Luo, Y. Jin, J. H. V. Nguyen, R. G. Hulet, B. A. Malomed, O. Marchukov, V. A. Yurovsky, V. Dunjko, M. Olshanii Solitons are nondispersive wave packets that arise as solutions to the onedimensional nonlinear Shr\"{o}dinger equation. Due to the integrability of the equation, after a specific interaction quench, a fundamental soliton may be transformed into a $n$thorder soliton composed of $n$ fundamental solitons, which are known as breathers.\footnote{V. E. Zakharov and A. B. Shabat, Soviet Physics JETP, 34, 1 (1972)}$^{,}$\footnote{J. Satsuma and N. Yajima, Prog. Theor. Phys. Supp. 55, 284 (1974)} The density profile oscillates in time, at a frequency determined by the chemical potential difference of the constituent solitons. A $n$soliton breather is formed with the mass ratio of the constituent solitons of 1:3:...:2$n$1, when the quench factor is $n^{2}$ where $n$ is an integer. In this work, we first form a soliton from a BoseEinstein condensate of $^{7}$Li atoms in a quasi1D harmonic potential formed from a single focused IR laser beam. We then quench the scattering length to form breathers. As we decrease the trap axial confinement strength sufficiently, the breathing frequency becomes independent of the axial confinement, which indicates that the geometry approaches the 1Dlimit. We observe the density profiles of the $n$=2 and $n$=3 breathers. [Preview Abstract] 
Thursday, June 4, 2020 2:24PM  2:36PM Live 
P06.00003: Quantum fluctuations of breather parameters in atomic condensates Vladimir Yurovsky, Oleksandr Marchukov, Boris Melamed, Maxim Olshanii, Vanja Dunjko, Randall Hulet A meanfield coldatom breather, which can be formed by the application of a fourfold quench of the scattering length to the fundamental soliton in an attractive quasionedimensional gas, is a nonlinear superposition of two solitons with the $1:3$ mass ratio and zero relative velocity. Formation of solitons with varying mass ratios and relative velocities, predicted by the Betheansatz analysis [1] of the quench for up to $N=23$ atoms, is a manifestation of quantum fluctuations. The fluctuations are analyzed here [2] within the Bogoliubov approach in the limit of large $N$, using two models of the vacuum state: white noise and correlated noise. The latter model, closer to the ab initio by construction, leads to a better agreement, within 20\% accuracy, with the fluctuations estimated from the Betheansatz results for small $N$. The variances of relative velocity, relative phase, initial distance, and soliton masses scale as $N$, $1/N$, $1/N^3$, and $N$, respectively. Effects of the trap potential on the quantum fluctuations are also analyzed. 1. V. A. Yurovsky, B. A. Malomed, R. G. Hulet, and M. Olshanii, Phys. Rev. Lett. 119, 220401 (2017). 2. O. V. Marchukov, B. A. Malomed, M. Olshanii, V. Dunjko, R. G. Hulet, and V. A. Yurovsky, arXiv:1911.01369. [Preview Abstract] 
Thursday, June 4, 2020 2:36PM  2:48PM On Demand 
P06.00004: Magnetic solitons in a spin1 BoseEinstein condensate Di Lao, Xiao Chai, Kazuya Fujimoto, Ryusuke Hamazaki, Masahito Ueda, Chandra Raman Vector soliton are a type of solitary wave packet occurring in a nonlinear medium comprised of multiple components. They have been discovered in a variety of systems including ultracold atoms. In this talk, we report the observation of a new type of soliton, called a magnetic soliton, in a spinor BEC beyond the usual Manakov limit of the 1dimensional GrossPitaevskii (GP) equations. By using a ``magnetic shadowing'' technique that only affects the spin and is therefore nondestructive, we created a pair of magnetic solitons in an antiferromagnetic spinor BEC. In addition, multiple solitons can be created by spatially modulating the pattern of the magnetic shadow, which allows the investigation of soliton interactions, collisions and possible bound states. [Preview Abstract] 
Thursday, June 4, 2020 2:48PM  3:00PM On Demand 
P06.00005: An Improved ManyBody Ansatz for a Hypervectorial Description of BoseEinstein Condensates Hyunwoo Lee, Chris Greene We present results on moving beyond the KHarmonic approximation for the adiabatic hypervectorial surface of a BoseEinstein condensate, which intuitively describes the longitudinal and transverse sizes of the collective system. The KHarmonic approximation freezes the hyperangular behavior of the manybody wavefunction to be that of the noninteracting state. Previous works show that the approximation describes the groundstate and the first excitation frequency reasonably well but qualitatively differs from the Bogoliubov theory for most other collective modes. Therefore, we develop a method for using the stationary state of the GrossPitaevskii equation as an alternative ansatz for the dominant hyperangular behavior. Of importance are the ThomasFermi regime and the quasionedimensional bright soliton, where the order parameter deviates significantly from a gaussian. In particular, for the bright soliton, the KHarmonic approximation predicts that the manybody spectrum should comprise of different Rydberg series of very large effective angular momentum, converging to thresholds defined by the transverse trap eigenstates. We discuss how the new method modifies the simple analytic behavior of KHarmonic surfaces, in comparison with the Bogoliubov theory. [Preview Abstract] 
Thursday, June 4, 2020 3:00PM  3:12PM On Demand 
P06.00006: Autonomous dark soliton detection Justyna Zwolak, Amilson Fritsch, Justin Elenewski, Ian Spielman Solitary waves (solitons) are nondispersing localized traveling waves that retain their size, shape, and speed as they move, and even when they collide with one another. In a repulsively interacting 1D BoseEinstein condensates (BEC), the soliton velocity governs the width, depth, and even stability of a soliton. To study solitons dynamics, a number of absorption images need to be manually analyzed to obtain the number of solitons present and their position. These solitons must be distinguished from a background of additional excitations. ~ We developed an automated twostep protocol for detecting dark solitons in twocomponent BECs. Our algorithm combines two neural networks pretrained using simulated and real data to: (1) identify the number of solitons present in BEC and (2) determine their position. This automated detector highlights the applicability of machine learningdriven feature detection, rather than traditional curve fitting, to streamline cold atom research. [Preview Abstract] 
Thursday, June 4, 2020 3:12PM  3:24PM 
P06.00007: Observation of quantum synchronization and blockade in spin1 atom Pratik Adhikary, Arif Warsi Laskar, Suprodip Mondal, Parag Katiyar, Sai Vinjanampathy, Saikat Ghosh synchronization between different physical systems has gained lots of attention in research. While in classical system, numerous research articles report the signature of synchronization, synchronization in the quantum regime has not been observed yet. We report the first observation of quantum synchronization in an ensemble of cold spin1 $^{\mathrm{87}}$Rb atoms. In particular, when we store and destructively interfere two dark state polaritons, we observe an otherwise delocalized limitcycle spin1 state gets localized and entrained to classically controlled phases, only in presence of artificially engineered, anisotropic decay channels, These observations are in accordance with the recent predictions of Roulet and Bruder of quantum phase synchronization in the smallest quantum systems, spin1 atoms, due to anisotropic internal decay channels. We numerically reconstruct the underlying quantum state and when viewed in phase space, in presence of artificially engineered asymmetric decay channels, we observe the state getting entrained even when the dark states interfere destructively. The corresponding relative phase difference of the dark state polaritons locks to a classical, controlled phase difference. Furthermore, we observe a blockade of synchronization due to quantum interference, a genuine quantum signature, which gets lifted due to increasing asymmetry in decays. When the system is driven harder, we observe emergence of Arnold tonguelike typical signatures of all synchronization. [Preview Abstract] 
Thursday, June 4, 2020 3:24PM  3:36PM 
P06.00008: Quenchproduced solitons in a boxtrapped BoseEinstein condensate Eli Halperin, John Bohn We describe a protocol to prepare solitons in a quasi1d boxtrapped BoseEinstein condensate using only a quench of the isotropic swave scattering length. A quench to exactly four times the initial scattering length creates one soliton at each boundary of the box, which then propagate in a uniform background density. No additional excitations are created during the quench. We investigate the robustness of this procedure to the scattering length ramp rate and an mismatch of the final scattering length. We additionally investigate the 3d regime, where the quench may cause excitations along the transverse directions of the elongated box, and give a procedure for minimizing these excitations even far away from the quasi1d regime via an additional quench of the transverse confining potential. [Preview Abstract] 
Thursday, June 4, 2020 3:36PM  3:48PM Not Participating 
P06.00009: Phase Diagram of Solitons in the Polar Phase of a Spin1 BoseEinstein Condensate ShihChuan Gou, IKang Liu, Hiromitsu Takeuchi We theoretically study the core structure of a stationary soliton, the building block of wallvortex composite defects recently observed in the polar phase of spin1 condensate [Seji Kang et. al., Phys. Rev. Lett. 122, 095301 (2019)], in the presence of quadratic Zeeman term. The phase diagram of such solitons is mapped out by locating the solutions of minimal soliton tension coefficient in the defining range of polar phase, and the states are distinguished into normal, antiferromagnetic, brokenaxisymmetry, and ferromagnetic phases according to the number and spin densities of the core. Phase boundaries and the associated orders of phase transitions are determined and the critical behavior of the relevant continuous phase transitions is analyzed using GinzburgLandau theory. [Preview Abstract] 
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