Condensate fraction in liquid 4He at zero temperature
Abstract
We present results of the one-body density matrix (OBDM) and the condensate fraction n0 of liquid 4He calculated at zero temperature by means of the Path Integral Ground State Monte Carlo method. This technique allows to generate a highly accurate approximation for the ground state wave function Psi0 in a totally model-independent way, that depends only on the Hamiltonian of the system and on the symmetry properties of Psi0. With this unbiased estimation of the OBDM, we obtain precise results for the condensate fraction n0 and the kinetic energy K of the system. The dependence of n0 with the pressure shows an excellent agreement of our results with recent experimental measurements. Above the melting pressure, overpressurized liquid 4He shows a small condensate fraction that has dropped to 0.8% at the highest pressure of p = 87 bar.
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