Spontaneous Emission in ultra-cold spin-polarised anisotropic Fermi Seas
  We examine and explain the spatial emission patterns of ultracold excited fermions in anisotropic trapping potentials in the presence of a spin polarised Fermi sea of ground state atoms. Due to the Pauli principle, the Fermi sea modifies the available phase space for the recoiling atom and thereby modifies its decay rate and the probability of the emitted photon's direction. We show that the spatial anisotropies are due to an intricate interplay between Fermi energies and degeneracy values of specific energy levels and identify a regime in which the emission will become completely directional. Our results are relevant for recent advances in trapping and manipulating cold fermionic samples experimentally and give an example of a conceptually new idea for a directional photon source. 
Brian O'Sullivan and Thomas Busch