Stability and dynamics across magnetic phases of nonlinear excitations in two-dimensional spinor Bose-Einstein condensates

The static properties, i.e., existence and stability, as well as the quench-induced dynamics of nonlinear excitations of the vortex-bright type appearing in two-dimensional harmonically confined spin-1 Bose-Einstein condensates are investigated. Linearly stable vortex-bright-vortex and bright-vortex-bright solutions arise in both antiferromagnetic and ferromagnetic spinor gases upon quadratic Zeeman energy shift variations. The precessional motion of such coherent structures is subsequently monitored dynamically. Deformations of the above configurations across the relevant transitions are exposed and discussed in detail. It is further found that stationary states involving highly quantized vortices can be realized in both settings. Spatial elongations, precessional motion and spiraling of the nonlinear excitations when exposed to finite temperatures and upon crossing the distinct phase boundaries, via quenching of the quadratic Zeeman coefficient, are unveiled. Spin-mixing processes triggered by the quench lead, among others, to changes in the waveform of the ensuing configurations. Our findings reveal an interplay between pattern formation and spin-mixing processes being accessible in contemporary cold atom experiments.

Exciton-polariton condensates in zero-, one-, and two-dimensional lattices

Microcavity exciton-polaritons are quantum quasi-particles arising from the strong light-matter coupling. They have exhibited rich quantum dynamics rooted from bosonic nature and inherent non-equilibrium condition. Dynamical condensation in microcavity exciton-polaritons has been observed at much elevated temperatures in comparison to ultrocold atom condensates. Recently, we have investigated the behavior of exciton-polariton condensates in artificial trap and lattice geometries in zero-dimension, one-dimension (1D) and two-dimension (2D). Coherent $pi$-state with p-wave order in a 1D condensate array and d-orbital state in a 2D square lattice are observed. We anticipate that the preparation of high-orbital condensates can be further extended to probe dynamical quantum phase transition in a controlled manner as quantum emulation applications.

Two-stream instability in quasi-one-dimensional Bose-Einstein condensates

We apply a kinetic model to predict the existence of an instability mechanism in elongated Bose-Einstein condensates. Our kinetic description, based on the Wigner formalism, is employed to highlight the existence of unstable Bogoliubov waves that may be excited in the counterpropagation configuration. We identify a dimensionless parameter, the Mach number at T = 0, that tunes different regimes of stability. We also estimate the magnitude of the main parameters at which two-stream instability is expected to be observed under typical experimental conditions.

Macroscopic Two-Dimensional Polariton Condensates

We report a record-size, two-dimensional polariton condensate of a fraction of a millimeter radius free from the presence of an exciton reservoir. This macroscopically occupied state is formed by the ballistically expanding polariton flow that relaxes and condenses over a large area outside of the excitation spot. The density of this trap-free condensate is < 1 polariton/{mu}m^2, reducing the phase noise induced by the interaction energy. Moreover, the backflow effect, recently predicted for the nonparabolic polariton dispersion, is observed here for the first time in the fast-expanding wave packet.

Quantum droplets of quasi-one-dimensional dipolar Bose-Einstein condensates

Ultracold dipolar droplets have been realized in a series of ground-breaking experiments, where the stability of the droplet state is attributed to beyond-mean-field effects in the form of the celebrated Lee-Huang-Yang (LHY) correction. We scrutinize the dipolar droplet states in a one-dimensional context using a combination of analytical and numerical approaches, and identify experimentally viable parameters for accessing our findings for future experiments. In particular we identify regimes of stability in the restricted geometry, finding multiple roton instabilities as well as regions supporting quasi-one-dimensional droplet states. By applying an interaction quench to the droplet, a modulational instability is induced and multiple droplets are produced, along with bright solitons and atomic radiation. We also assess the droplets robustness to collisions, revealing population transfer and droplet fission.