Monte Carlo Simulations of the Unitary Bose Gas

We investigate the zero-temperature properties of a diluted homogeneous Bose gas made of $N$ particles interacting via a two-body square-well potential by perfor ming Monte Carlo simulations. We tune the interaction strength to achieve arbitrary positive values of the scattering length and compute by Monte Carlo quadrature the energy per particle $E/N$ and the condensate fraction $N_0/N$ of this system by using a Jastrow ansatz for the many-body wave function which avoids the formation of the self-bound ground-state and describes instead a (metastable) gaseous state with uniform den sity. In the unitarity limit, where the scattering length diverges while the range of the inter-atomic potential is much smaller than the average distance between atoms, we find a finite energy per particle ($E/N=0.70\ \hbar^2(6\pi^2n)^{2/3}/2m$, with $n$ th e number density) and a quite large condensate fraction ($N_0/N=0.83$).