  Performances of work-to-work conversion are studied for a dissipative
nonlinear quantum system with two isochromatic phase-shifted drives. It is
shown that for weak Ohmic damping simultaneous maximization of efficiency with
finite power yield and low power fluctuations can be achieved. Optimal
performances of these three quantities are accompanied by a shortfall of the
trade-off bound recently introduced for classical thermal machines. This bound
can be undercut down to zero for sufficiently low temperature and weak
dissipation, where the non-Markovian quantum nature dominates. Analytic results
are given for linear thermodynamics. These general features can persist in the
nonlinear driving regime near to a maximum of the power yield and a minimum of
the power fluctuations. This broadens the scope to a new operation field beyond
linear response.
