Observation of Weak Collapse in a Bose-Einstein Condensate

PHYSICAL REVIEW X 6:4 (2016) ARTN 041058

Authors:

C Eigen, AL Gaunt, A Suleymanzade, N Navon, Z Hadzibabic, RP Smith

Abstract:

We study the collapse of an attractive atomic Bose-Einstein condensate prepared in the uniform potential of an optical-box trap. We characterize the critical point for collapse and the collapse dynamics, observing universal behavior in agreement with theoretical expectations. Most importantly, we observe a clear experimental signature of the counterintuitive weak collapse, namely, that making the system more unstable can result in a smaller particle loss. We experimentally determine the scaling laws that govern the weak-collapse atom loss, providing a benchmark for the general theories of nonlinear wave phenomena.

Emergence of a turbulent cascade in a quantum gas.

Nature 539:7627 (2016) 72-75

Authors:

N Navon, AL Gaunt, RP Smith, Z Hadzibabic

Abstract:

A central concept in the modern understanding of turbulence is the existence of cascades of excitations from large to small length scales, or vice versa. This concept was introduced in 1941 by Kolmogorov and Obukhov, and such cascades have since been observed in various systems, including interplanetary plasmas, supernovae, ocean waves and financial markets. Despite much progress, a quantitative understanding of turbulence remains a challenge, owing to the interplay between many length scales that makes theoretical simulations of realistic experimental conditions difficult. Here we observe the emergence of a turbulent cascade in a weakly interacting homogeneous Bose gas-a quantum fluid that can be theoretically described on all relevant length scales. We prepare a Bose-Einstein condensate in an optical box, drive it out of equilibrium with an oscillating force that pumps energy into the system at the largest length scale, study its nonlinear response to the periodic drive, and observe a gradual development of a cascade characterized by an isotropic power-law distribution in momentum space. We numerically model our experiments using the Gross-Pitaevskii equation and find excellent agreement with the measurements. Our experiments establish the uniform Bose gas as a promising new medium for investigating many aspects of turbulence, including the interplay between vortex and wave turbulence, and the relative importance of quantum and classical effects.

Superconductivity in graphite intercalation compounds

Physica C Superconductivity Elsevier 514 (2015) 50-58

Authors:

Robert P Smith, Thomas E Weller, Christopher A Howard, Mark PM Dean, Kaveh C Rahnejat, Siddharth S Saxena, Mark Ellerby

Connecting Berezinskii-Kosterlitz-Thouless and BEC Phase Transitions by Tuning Interactions in a Trapped Gas.

Physical review letters 114:25 (2015) 255302

Authors:

Richard J Fletcher, Martin Robert-de-Saint-Vincent, Jay Man, Nir Navon, Robert P Smith, Konrad GH Viebahn, Zoran Hadzibabic

Abstract:

We study the critical point for the emergence of coherence in a harmonically trapped two-dimensional Bose gas with tunable interactions. Over a wide range of interaction strengths we find excellent agreement with the classical-field predictions for the critical point of the Berezinskii-Kosterlitz-Thouless (BKT) superfluid transition. This allows us to quantitatively show, without any free parameters, that the interaction-driven BKT transition smoothly converges onto the purely quantum-statistical Bose-Einstein condensation transition in the limit of vanishing interactions.

Critical dynamics of spontaneous symmetry breaking in a homogeneous Bose gas

Science American Association for the Advancement of Science (AAAS) 347:6218 (2015) 167-170

Authors:

Nir Navon, Alexander L Gaunt, Robert P Smith, Zoran Hadzibabic

Abstract:

Breaking the symmetry in an atomic gas Cooling a physical system through a phase transition typically makes it less symmetrical. If the cooling is done very slowly, this symmetry change is uniform throughout the system. For a faster cooling process, the system breaks up into domains: The faster the cooling, the smaller the domains. Navon et al. studied this process in an ultracold gas of Rb atoms near its transition to a condensed state (see the Perspective by Ferrari). The authors found that the size of the domains froze in time in the vicinity of the transition and that it depended on the cooling speed, as predicted by theory. Science , this issue p. 167 ; see also p. 127