  We review on a recently proposed quantum exception to the second law of
thermodynamics. We emphasize that $^4$He superflows, like any other forms of
flows, shall carry entropy or heat in a thermal environment. Following that,
one can use a heterogeneous $^4$He superflow loop to realize entropy-decreasing
processes. We also mention that the heat content of a superflow has an unusual
dependence on flow velocity, which is an important factor contributing to the
entropy-decreasing processes.
