  Quantum fluctuations, which result from the Heisenberg uncertainty principle,
explain a number of physical observations, from the finite mass of elementary
particles to the Lamb shift in hydrogen and the Casimir effect. The local
violation of the conservation of energy raises the question of whether the
energy of quantum fluctuations can sustain the cycle of a quantum engine. So
far, a proposal has hinted that this is possible, but contains important
caveats. In this Letter, we predict that quantum fluctuations can power an
autonomous spintronic quantum information engine by converting entanglement
energy into useful electrical work. Our two-stroke engine operates on two
entangled spin quantum dots (QDs) that are connected in series with two fully
spin-polarized baths. The ultrafast measurement stroke breaks the entanglement,
thereby energizing the system on average. This energy is released into the
leads as electrical current when the thermalizing stroke equilibrates the QDs
with the electrode baths. Using a master equation approach, we analytically
demonstrate the efficiency of the quantum fluctuation-driven engine, and we
study the cycle numerically to gain insight into the relevant parameters to
maximize power. Our results suggest that quantum fluctuations and the
measurement back-action alone cannot explain prior experimental results.
Measuring the spin dynamics of the engine's ferromagnetic electrodes should
help determine its efficiency. This electronically driven feedback on quantum
entanglement should also boost quantum chemistry, biology and cognition.
