We consider the ground state properties of a trapped dipolar condensate under the influence of quantum fluctuations. We show that this system can undergo a phase transition from a low density condensate state to a high density droplet state, which is stabilized by quantum fluctuations. The energetically favored state depends on the geometry of the confining potential, the number of atoms and the two-body interactions. We develop a simple variational ansatz and validate it against full numerical solutions. We produce a phase diagram for the system and present results relevant to current experiments with dysprosium and erbium condensates.

We demonstrate that a dipolar condensate can be prepared into a three-dimensional wavepacket that remains localized when released in free-space. Such self-bound states arise from the interplay of the two-body interactions and quantum fluctuations. We develop a phase diagram for the parameter regimes where these self-bound states are stable, examine their properties, and demonstrate how they can be produced in current experiments.

Fusobacterium nucleatum is closely associated with human periodontal diseases and may also be a causative agent in other infections, such as pericarditis, septic arthritis, and abscesses of tonsils and liver. Initiation and outcome of infective diseases depend critically on the host cell signaling system altered by the microbe. Production of proteinases by infected cells is an important factor in pericellular tissue destruction and cell migration. We studied binding of F. nucleatum to human epithelial cells (HaCaT keratinocyte line) and subsequent cell signaling related to collagenase 3 expression, cell motility, and cell survival, using a scratch wound cell culture model. F. nucleatum increased levels of 12 protein kinases involved in cell migration, proliferation, and cell survival signaling, as assessed by the Kinetworks immunoblotting system. Epithelial cells of the artificial wound margins were clearly preferential targets of F. nucleatum. The bacterium colocalized with lysosomal structures and stimulated migration of these cells. Of the 13 anaerobic oral bacterial species, F. nucleatum and Fusobacterium necrophorum were among the best inducers of collagenase 3 mRNA levels, a powerful matrix metalloproteinase. Production of collagenase 3 was detected in fusobacterium-infected cells and cell culture medium by immunocytochemistry, immunoblotting, and zymography. The proteinase production involved activation of p38 mitogen-activated protein kinase in the infected cells. The study suggests that F. nucleatum may be involved in the pathogenesis of periodontal diseases (and other infections) by activating multiple cell signaling systems that lead to stimulation of collagenase 3 expression and increased migration and survival of the infected epithelial cells.

We calculate the collective excitations of a dipolar Bose-Einstein condensate in the regime where it self-binds into droplets stabilized by quantum fluctuations. We show that the filament-shaped droplets act as a quasi-onedimensional waveguide along which low angular momentum phonons propagate. The evaporation (unbinding) threshold occurring as the atom number N is reduced to the critical value Nc is associated with a monopole-like excitation going soft as 0 ∼ (N − Nc) 1/4 . Considering the system in the presence of a trapping potential, we quantify the crossover from a trap-bound condensate to a self-bound droplet.Dipolar condensates consist of atoms with appreciable magnetic dipole moments that interact with a long-ranged and anisotropic dipole-dipole interaction (DDI). Recent experiments with dipolar condensates of dysprosium [1][2][3] and erbium [4] atoms have observed the formation of self-bound droplets that can preserve their form, even in the absence of any external confinement. These droplets occur in the dipoledominated regime, where the DDIs dominate over shortranged (s-wave) interactions, and for sufficiently many atoms in the droplet [5,6]. In the dipole-dominated regime meanfield theory predicts that the condensate is unstable to collapse, but as collapse begins and the density increases the (beyond meanfield) quantum fluctuation corrections become important. These Lee-Huang-Yang (LHY) [7] corrections [8][9][10] contribute an energy that can arrest the collapse and stabilize the system as a finite sized droplet [11][12][13]. Experiments have produced droplets by ramping a trapped condensate into the dipole dominated regime leading to a single droplet or an array of droplets forming, depending on trap geometry [12][13][14]. Droplets with atom numbers in the range 10 3 -10 4 have been observed, with peak densities predicted to be an order of magnitude higher than the initial condensate density (> 10 21 m −3). The droplets are still well within the dilute weakly interacting regime, but three-body recombination becomes an important source of atom loss that limits droplet lifetime. Lifetimes of up to ∼ 100 ms were measured for free-space droplets [3], with longer times observed for trapped droplets (e.g. [1]). The anisotropic DDI causes droplets to elongate along the direction that the dipoles are polarized into highly anisotropic filaments.It is desirable to have a comprehensive understanding of the full excitation spectrum of the droplets. Indeed, in helium nanodroplets [15], which are dense self-bound superfluid droplets, the various types of bulk and surface excitations have been extensively studied for decades (e.g. see [16,17]). Already some first steps have been made in dipolar droplets, with Wächtler et al. using a variational ansatz to characterize three shape oscillations [6], with their prediction for the frequency of the axial mode comparing favorably to experiments with erbium [4]. Here we present the results of the first calculations of the full excitation spectrum of a dipolar condensate ...