Coarsening Dynamics of Domains in Lipid Membranes

We investigate isothermal diffusion and growth of micron-scale liquid domains within membranes of free-floating giant unilamellar vesicles with diameters between 80 and 250 Am. Domains appear after a rapid temperature quench, when the membrane is cooled through a miscibility phase transition such that coexisting liquid phases form. In membranes quenched far from a miscibility critical point, circular domains nucleate and then progress within seconds to late stage coarsening in which domains grow via two mechanisms 1), collision and coalescence of liquid domains, and 2), Ostwald ripening. Both mechanisms are expected to yield the same growth exponent, alpha = 1/3, where domain radius grows as time(alpha). We measure alpha = 0.28 +/- 0.05, in excellent agreement. In membranes close to a miscibility critical point, the two liquid phases in the membrane are bicontinuous. A quench near the critical composition results in rapid changes in morphology of elongated domains. In this case, we measure alpha = 0.50 +/- 0.16, consistent with theory and simulation

Schrodinger Cats in Double Well Bose Condensates: Modeling Their Collapse and Detection via Quantum State Diffusion

Can macroscopic quantum superposition states (or highly entangled number states) be observed directly\u27? Specifically, can phase contrast imaging be applied to observe a superposition state with essentially all of the atoms in a gaseous double well BEG being simultaneously in both wells at the same time\u27? That is we are looking to image states of the type vertical bar N, 0 \u3e +vertical bar 0, N \u3e where vertical bar L, R \u3e denotes L particles in the Left well and R. in the Right. We will happily settle for states of the form IN n, n \u3e +In, N is \u3e, with 71, \u3c\u3c N, these being less ephemeral. Earlier work in our group, Perry, Reinhardt and Kahn, has shown that such highly entangled number states may be generated by appropriate phase engineering, just as in the case of the phase engineering of solitons in single well BECs. Experimentalists have been hesitant to attempt to create such states in fear that definitive observations cannot be carried out. There have also been suggestions that Nature will prevent such superpositions from existing for N too large... and thus there are also basic issues in quantum theory which may prevent the formation and detection of such states. In the present progress report we begin an investigation of calculating the lifetimes of such entangled states in the presence of both observation and spontaneous decay both of which perturb, and eventually destroy, the entanglement under investigation via quantum back-action. Quantum State Diffusion (QSD) provides a useful computational tool in addressing such questions, and we present the initial results of exploring this novel use of QSD