Illustration of universal relations for trapped four-fermion system with arbitrary s-wave scattering length

A two-component four-fermion system with equal masses, interspecies s-wave scattering length a and vanishing intraspecies interactions under external spherically symmetric harmonic confinement is considered. Using a correlated Gaussian basis set expansion approach, we determine the energies and various structural properties of the energetically lowest-lying gas-like state throughout the crossover for various ranges of the underlying two-body potential. Extrapolating to the zero-range limit, our numerical results show explicitly that the total energy, the trap energy as well as certain aspects of the pair distribution function and of the momentum distribution are related through the so-called integrated contact intensity I(a). Furthermore, it is shown explicitly that the total energy and the trap energy are related through a generalized virial theorem that accounts for a non-zero range.
Comment: 9 figures with several subfigures