  We study how to achieve the ultimate power in the simplest, yet non trivial,
model of a thermal machine, namely a two-level quantum system coupled to two
thermal baths. Without making any prior assumption on the protocol, via optimal
control we show that, regardless of the microscopic details and of the
operating mode of the thermal machine, the maximum power is universally
achieved by a fast Otto-cycle like structure in which the controls are rapidly
switched between two extremal values. A closed formula for the maximum power is
derived, and finite-speed effects are discussed. We also analyse the associated
efficiency at maximum power (EMP) showing that, contrary to universal results
derived in the slow-driving regime, it can approach Carnot's efficiency, no
other universal bounds being allowed.
