Dr. I-Kang Liu, Newcastle University, about:
Coherent and incoherent structures in fuzzy dark matter halos
Dark matter(DM) halos composed of ultralight bosons exhibit wavy behaviour with de Broglie wavelengthin cosmological scales, known as fuzzy DM (FDM), wave DM or BECDM. To the leading order of the space-time metric, the effective equation of motion is the Schrodinger-Poison system of equation, a classical-field wavefunction coupled to Newtonian gravity, and is reminiscentof the universal phenomenon of Bose-Einstein condensation(BEC), described by a macroscopic condensate wavefunction.
This model reproduces the density distribution in large length scales in the cold DM model, called Navarro–Frenk–White profile, and can be a candidate to resolve the missing-satellite, too-big-to-fail and cusp-core problems with a compact solitonic core in the centre of a halo. Here inspired by widely-studied laboratory atomic systems we systematically examine the BEC concept by examining the field fluctuations in fuzzy dark matter halos, generated by our merger simulations, via probing the spatial phase-phase and density-density correlation functions to unveil the FDM halo properties. We find out that the solitonic core is fully coherent and coincides with the Penrose-Onsager condensate mode, exhibiting off-diagonal-long-range order, of a virialized halo. Moving outward from the core, fluctuations enhance and the bimodal fit of the core-halo profile can nicely capture the crossover length scale. By looking at the energy distribution, we demonstrate that these fluctuations are mainly sourced by a large number of quantized vortices, indicating a turbulence-like state, which is persistent in our simulation. In addition, the intervortex distance scale matches the granule one by comparing the vortex energy and overdensity power spectra. This work provides a new picture to investigate the FDM halos.
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Dr. Christian Ott, Max-Planck-Institut für Kernphysik, Heidelberg, about:
Site-specific and state-resolved coherent quantum control of atoms and molecules
Using intense ultrashort laser pulses with a duration across the femtosecond and attosecond timescale, it is possible to couple and control multi-electron transitions which involve short-lived states in atoms and molecules. Their extreme-ultraviolet (XUV) and x-ray absorption spectra hereby encode the time-resolved dynamics with state-specific spectroscopic information about the relevant quantum states. In this talk, I will first provide an overview how we extract quantum-dynamics information from spectral absorption line shapes. We will discuss for instance the laser-controlled transformation of Fano to Lorentzian spectral line shapes of a correlated two-electron transition in helium, and how its absorption profile coherently builds up on the femtosecond timescale. We will further apply these concepts to nonlinear absorption spectroscopy with free-electron lasers and discuss XUV-induced energy shifts of strongly coupled states, e.g., in helium and neon atoms. Finally, we will also look at time-resolved measurements with XUV-pump – XUV-probe absorption spectroscopy to resolve the state-specific dynamics in small molecules, accessing structural dynamics from the perspective of individual electronic states. With all these experiments, we explore new methods of nonlinear light-matter interaction for the quantum control of atoms and molecules down to the natural attosecond timescale of the electron motion and coherently addressing specific transitions of individual constituents within the larger quantum system.
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