Condensate fraction in liquid 4He at zero temperature

Abstract

We present results of the one-body density matrix (OBDM) and the condensate fraction n_0 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 Psi_0 in a totally model-independent way, that depends only on the Hamiltonian of the system and on the symmetry properties of Psi_0. With this unbiased estimation of the OBDM, we obtain precise results for the condensate fraction n_0 and the kinetic energy K of the system. The dependence of n_0 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.

12 pages. 4 figures. Accepted for publication on "Journal of Low Temperature Physics"

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• Exact ground state Monte Carlo method for Bosons without importance sampling
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• Temperature Dependence of the Vacancy Formation Energy in Solid ${}^4$He
• Momentum distribution of liquid 4He across the normal-superfluid phase transition
• Microscopic picture of superfluid ${}^4$He