We observed and controlled the Brownian motion of solitons. We launched solitonic excitations in highly elongated Rb-87 Bose-Einstein condensates (BECs) and showed that a dilute background of impurity atoms in a different internal state dramatically affects the soliton. With no impurities and in one dimension (1D), these solitons would have an infinite lifetime, a consequence of integrability. In our experiment, the added impurities scatter off the much larger soliton, contributing to its Brownian motion and decreasing its lifetime. We describe the soliton{\textquoteright}s diffusive behavior using a quasi-1D scattering theory of impurity atoms interacting with a soliton, giving diffusion coefficients consistent with experiment.

}, issn = {0027-8424}, doi = {10.1073/pnas.1615004114}, author = {Aycock, Lauren M. and Hurst, Hilary M. and Efimkin, Dmitry K. and Genkina, Dina and Lu, Hsin-I and Galitski, Victor M. and Ian B Spielman} } @article {ISI:000400652700006, title = {Kinetic theory of dark solitons with tunable friction}, journal = {PHYSICAL REVIEW A}, volume = {95}, number = {5}, year = {2017}, month = {MAY 3}, abstract = {We study controllable friction in a system consisting of a dark soliton in a one-dimensional Bose-Einstein condensate coupled to a noninteracting Fermi gas. The fermions act as impurity atoms, not part of the original condensate, that scatter off of the soliton. We study semiclassical dynamics of the dark soliton, a particlelike object with negative mass, and calculate its friction coefficient. Surprisingly, it depends periodically on the ratio of interspecies (impurity-condensate) to intraspecies (condensate-condensate) interaction strengths. By tuning this ratio, one can access a regime where the friction coefficient vanishes. We develop a general theory of stochastic dynamics for negative-mass objects and find that their dynamics are drastically different from their positive-mass counterparts: they do not undergo Brownian motion. From the exact phase-space probability distribution function (i.e., in position and velocity), we find that both the trajectory and lifetime of the soliton are altered by friction, and the soliton can undergo Brownian motion only in the presence of friction and a confining potential. These results agree qualitatively with experimental observations by Aycock et al. {[}Proc. Natl. Acad. Sci. USA 114, 2503 (2017)] in a similar system with bosonic impurity scatterers.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.95.053604}, author = {Hurst, Hilary M. and Efimkin, Dmitry K. and Ian B Spielman and Galitski, Victor} } @article {ISI:000390246200008, title = {Real-space mean-field theory of a spin-1 Bose gas in synthetic dimensions}, journal = {PHYSICAL REVIEW A}, volume = {94}, number = {6}, year = {2016}, month = {DEC 15}, pages = {063613}, abstract = {The internal degrees of freedom provided by ultracold atoms provide a route for realizing higher dimensional physics in systems with limited spatial dimensions. Nonspatial degrees of freedom in these systems are dubbed {\textquoteleft}{\textquoteleft}synthetic dimensions.{{\textquoteright}{\textquoteright}} This connection is useful from an experimental standpoint but complicated by the fact that interactions alter the condensate ground state. Here we use the Gross-Pitaevskii equation to study the ground-state properties of a spin-1 Bose gas under the combined influence of an optical lattice, spatially varying spin-orbit coupling, and interactions at the mean-field level. The associated phases depend on the sign of the spin-dependent interaction parameter and the strength of the spin-orbit field. We find {\textquoteleft}{\textquoteleft}charge{{\textquoteright}{\textquoteright}}- and spin-density-wave phases which are directly related to helical spin order in real space and affect the behavior of edge currents in the synthetic dimension. We determine the resulting phase diagram as a function of the spin-orbit coupling and spin-dependent interaction strength, considering both attractive (ferromagnetic) and repulsive (polar) spin-dependent interactions, and we provide a direct comparison of our results with the noninteracting case. Our findings are applicable to current and future experiments, specifically with Rb-87, Li-7, K-41, and Na-23.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.94.063613}, author = {Hurst, Hilary M. and Wilson, Justin H. and Pixley, J. H. and Ian B Spielman and Natu, Stefan S.} } @article { ISI:000377301200003, title = {Transport of Dirac electrons in a random magnetic field in topological heterostructures}, journal = {PHYSICAL REVIEW B}, volume = {93}, number = {24}, year = {2016}, month = {JUN 6}, issn = {2469-9950}, doi = {10.1103/PhysRevB.93.245111}, author = {Hurst, Hilary M. and Efimkin, Dmitry K. and Galitski, Victor} } @article { ISI:000350276400002, title = {Charged skyrmions on the surface of a topological insulator}, journal = {PHYSICAL REVIEW B}, volume = {91}, number = {6}, year = {2015}, month = {FEB 18}, issn = {1098-0121}, doi = {10.1103/PhysRevB.91.060401}, author = {Hurst, Hilary M. and Efimkin, Dmitry K. and Zang, Jiadong and Victor M Galitski} }