Thursdays 4:00 p.m. 104 Physics. Colloquium organizer: Dr. Simeon Mistakidis <smystakidis@mst.edu>

Link to main colloquium page

Turbulence is a non-equilibrium phenomenon in fluid mechanics involving energy cascades across multiple length scales [1]. It is encountered in a plethora of systems such as plasma, water and planetary waves. Turbulent behavior has also been observed in low temperature quantum gases, whose collective motion can be regarded as that of a nonviscous fluid (superfluids). The advantages of the latter is that they allow for a multiscale analysis of turbulent cascades, both theoretically and experimentally [2].

Here, we are interested in the turbulent behavior of gases possessing strong dipole moments, significantly departing from classical fluids [3]. In particular, depending on the strength of dipole interactions, a crystalline structure can appear on top of the superfluid flow, the supersolid. When dipolar gases are driven across the superfluid-supersolid transition, the momentum distributions display a power-law behavior at large momenta, the smoking gun of turbulent behavior. The initial distribution is quite extended in the case of a supersolid, leading to the fast establishment of the non-equilibrium steady-state compared to a superfluid.

[1] U. Frisch, Turbulence: the legacy of AN Kolmogorov (Cambridge university press), 1995.

[2] Gałka et al, Phys. Rev. Lett. 129, 190402 (2022).

[3] Chomaz et al, Rep. Prog. Phys. 86, 026401 (2022).

The inhomogeneous Universe, as revealed by fluctuations in the cosmic microwave background (CMB) radiation and large-scale structure surveys, offers critical insights into fundamental physics. Studying the Universe’s large-scale structure at high redshifts (2 < z < 6, ~10 to 12.8 billion years ago) is crucial for probing the metric, particle content, and periods of accelerated expansion such as Inflation and Dark Energy. Efficient redshift determination for faint galaxies across wide areas, especially at high redshifts, is challenging. However, Lyman Alpha Emitters (LAEs), which exhibit bright Lyα emission lines, simplify this process. The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) aims to detect and measure the redshifts of over one million LAEs between 1.88 < z < 3.52 (~10 to 11 billion years ago). Beyond cosmological measurements, these data enable studies of Lyα spectral profiles and the underlying radiative transfer, improving our understanding of LAEs and aiding in distinguishing true LAEs from false detections. This, in turn, helps constrain measurements of the Hubble Parameter, and Angular Diameter Distance, crucial for cosmology. In this talk, I will present an empirical approach to modeling Lyman Alpha Emitting galaxies within the HETDEX survey. Our model integrates a dark matter N-body simulation with an empirical galaxy-halo relationship. Lyα photon escape and line profiles are based on Monte Carlo radiative transfer calculations sensitive to local astrophysical conditions. The observability of Lyα photons is linked to the intergalactic medium’s large-scale properties. Our model is calibrated against LAE luminosity functions and clustering analyses, offering a valuable tool for HETDEX pipeline validation and understanding the LAE-halo connection.

Advanced LIGO and Virgo have detected gravitational waves from compact merging binaries from the four observing runs. The next discovery could be associated with other astrophysical sources. Core-collapse supernova is one of the most promising candidates and multi-messenger sources. It can be detected electromagnetically, as well as via gravitational waves and neutrinos. Detecting gravitational waves emitted from core-collapse supernova will allow for direct investigations of the engine-driving explosion's dynamics. In this talk, I will provide an overview of gravitational waves from core-collapse supernovae, discuss the search methodologies, and present the search results from recent supernova candidates.

In the first part, we delve into the world of Rydberg excitons, highly excited bound states of electrons and holes in semiconductors, showcasing their ability to induce significant optical nonlinearities in crystals. Ongoing efforts to push these nonlinearities to the ultimate quantum limit of single photons will also be discussed.

The second part provides an overview of recent progress on giant diatomic molecules composed of two Rydberg atoms (Rydberg macrodimers), excited from an optical lattice. These molecules feature an intriguing binding mechanism mediated by van der Waals forces. We will explore how Rydberg macrodimers can be optically coupled to a continuum of free motional states, leading to the formation of multi-atom molecules bound by light.

Neutron star mergers as materials science

In this presentation, I will introduce BECs and highlight ongoing experiments in quantum hydrodynamics conducted in our lab at Washington State University. The formation of vortices, solitons, and dispersive shocks are just a few examples of the dynamical richness of this field. Our recent work focuses on leveraging multicomponent systems to mimic single-component behavior with modified interactions, facilitating the observation of Peregrine solitons. Additionally, in the non-interacting regime, recent experiments have revealed extensive interference fringes along caustics in atomic matter flow, showcasing the broad scope of dispersive hydrodynamics in matter waves.

**Title: "From Nonlinear Optics to Ultra-Cold Atomic Physics and Rogue Waves: Adventures in Applied and Computational Mathematics"****Abstract**: Complex systems are ubiquitous in nature and human-designed environments. The overarching goal of our research is to leverage advanced computational methods with fundamental theoretical analysis to model the nonlinear behavior of systems that are not otherwise amenable to integrable systems techniques. Examples include: Studies of superfluidity and superconductivity in ultra-cold atomic physics (e.g., Bose-Einstein condensation), extreme and rare events (e.g., tsunamis and rogue waves), and collapse phenomena in optics (e.g., light propagation through a medium without diffraction). We have developed computational methods for bifurcation analysis that explain the structure of the parameter space of these systems and continuation methods (pseudo-arclength and Deflated Continuation Method (DCM)) for efficient tracking of solution branches and connecting them to physical observations. The objective is to enable technological innovations, such as the discovery of new materials and development of devices for precision measurements (e.g., interferometers), or to predict extreme phenomena based on the features of the eigenvalue spectra of the system.

Inconspicuous solutions of the Nonlinear Schrödinger (NLS) equation were discovered by developing DCM specifically for NLS to uncover previously unknown behavior and weakly nonlinear unstable solutions that are potential targets for experimental verification. Furthermore, a novel Kuznetsov-Ma breather (time-periodic) solution to the discrete and non-integrable NLS equation relevant to predicting periodic extreme and rare events in optical systems was discovered by employing pseudo-arclength continuation. The combination of perturbation methods with pseudo-arclength continuation enabled the elucidation of collapsing waveforms associated with the 1D focusing NLS and Korteweg-de Vries equations. Future research will focus on the development of computational tools for numerical simulation of complex nonlinear systems with the ultimate goal being the dissemination of an open-source library that can be used to study bifurcations and perform stability analysis of such systems.

We will dive deep into the history of neutrino discovery, to how these elusive particles have challenged our understanding of the universe. Despite their abundance, many mysteries surrounding neutrinos remain unsolved: Do they have mass? If so, how much? Why do they oscillate between different types, or flavors, as they travel through space? And what implications do these properties have for our understanding of the early universe and the matter-antimatter asymmetry?

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