Calculation of the Condensate Fraction in Liquid Helium-4

We adduce the results of the condensate fraction calculation for liquid helium-4. The method is derived from the first principles and involves minimum assumptions. The only experimental quantity we need in our calculations is the static structure factor which is easily measurable. We use the approximation in which expressions contain one summation in the wave vector space (or one integration it the radius vector space) in order to demonstrate the validity of our method. The computed values of the condensate fraction lie within 8.8 ÷ 14% depending on the model potential for the short-range interaction. This result agrees with recent experimental measurements and numerical estimations.