Maurizio Rossi — Università di Padova #
The challenge 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 performing 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 
density. <br/>
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 \(n\) the number density) and a quite large 
condensate fraction (\(N_0/N=0.83\)) [1]. <br/>
Starting from the obtained equation of state we study also the frequencies of the monopole and 
quadrupole oscillations of the gas trapped in a isotropic harmonic potential within Density 
Functional Theory in the Local Density approximation. We include also the damping effect of 
three-body losses on such modes [2]. <br/>
Prompted by the very recent experimental data of \(^{85}\)Rb atoms at unitarity [3] we focus on the 
momentum distribution as a function of time. Our results suggest that at unitarity, a 
quasi-stationary momentum distribution is reached at low momenta after a long transient, contrary 
to what found experimentally for large momenta which equilibrate on a time scale shorter than the 
one for three body losses [4]. <br/><br/>

References<br/> 
1. M. Rossi, L. Salasnich, F. Ancilotto and F. Toigo,  Phys. Rev. A  <b>89</b>, 041602(R) (2014) <br/> 
2. M. Rossi, F. Ancilotto, L. Salasnich and F. Toigo, arXiv:1408.3945  (accepted in EPJ) <br/>
3. P. Makotyn, C.E. Klauss, D.L. Goldberger, E.A. Cornell and  D.S. Jin,  Nature Phys. <b>10</b>, 
   116 (2014) <br/>
4. F. Ancilotto, M. Rossi, L. Salasnich and F. Toigo, arXiv:1501.05491 (accepted in FBSY)  <br/>