Zero-fluctuation quantum work extraction

We study the possibility of deterministic protocols for extracting work from quantum systems. Focusing on the two-point measurement work extraction scenario, we prove that, with enough copies of the system, such zero-fluctuation protocols always exist if the Hamiltonian has a rational spectrum. Leveraging this result, we show that for any Hamiltonian, it is possible to construct a unitary driving protocol on sufficiently many copies of the system with work fluctuations strictly bounded within an arbitrary interval +/- δ, albeit requiring exponentially many copies in 1/δ.