Harnessing Higher-Dimensional Fluctuations in an Information Engine.

We study the optimal performance of an information engine consisting of an overdamped Brownian bead confined in a controllable, d-dimensional harmonic trap and additionally subjected to gravity. The trap's center is updated dynamically via a feedback protocol designed such that no external work is done by the trap on the bead while maximizing the extraction of gravitational potential energy and achieving directed motion. We show that performance improves when thermal fluctuations in directions perpendicular to gravity are harnessed. This improvement arises from feedback cooling of these transverse degrees of freedom, along which all heat is extracted. Strikingly, engines based on a single transverse degree of freedom already outperform engines based solely on vertical (z) measurements. This engine design modularizes the functions of harnessing fluctuations and storing free energy, drawing a close analogy to the Szilard engine.