  We propose to study the Brownian motion of a classical microsphere submerged
in superfluid $^4$He using the recent laser technology as a direct
investigation of the thermal fluctuations of quasiparticles in the quantum
fluid. By calculating the temperature dependence of both the friction
coefficient and the strength of the random force, we show that the resonant
mode of the fluctuational motion can be fully resolved by the present
technology. Contrary to the previous work, it is found that the roton
contribution is not negligible, and it even becomes dominant when the
temperature is above 0.76\,K.
