  It was recently found that the information-to-work conversion in a quantum
Szilard engine can be increased by using a working medium of bosons with
attractive interactions. In the original scheme, the work output depends on the
insertion and removal position of an impenetrable barrier that acts like a
piston, separating the chambers of the engine. Here, we show that the barrier
removal process can be made fully reversible, resulting in a full
information-to-work conversion if we also allow for the interaction strength to
change during the cycle. Hence, it becomes possible to reach the maximum work
output per cycle dictated by the second law of thermodynamics. These findings
can, for instance, be experimentally verified with ultra-cold atoms as a
working medium, where a change of interaction strength can be controlled by
Feshbach resonances.
