  We present a critical examination of the difficulties with the quantum
versions of a lifted weight that are widely used as work storage systems in
quantum thermodynamics. To overcome those difficulties, we turn to the strong
connections between information and thermodynamics illuminated by Szilard's
engine and Landauer's principle, and consider the concept of informational work
storage. This concept is in sharp contrast with the usual one of mechanical
work storage underlying the idealization of a quantum weight. An informational
work storage system based on maximally mixed qubits that does not act as an
entropy sink and is capable of truly distinguishing work from heat is studied.
Applying it to the problem of single-shot work extraction in various extraction
schemes, we show that for a given system state the maximum extractable work is
independent of extraction scheme, in accordance with the second law of
thermodynamics.
