Covering a broad spectrum of different modes of operations of engines with a working substance having just two quantum states, the researchers found that only for idealized cycles that perform infinitely slowly it makes no difference which monitoring scheme is applied. But all engines that run in finite time and hence are of practical interest work considerably better for their power output and reliability when they are monitored according to the repeated contact scheme.
Confined to a piston, which undergoes four subsequent strokes: it is first compressed, then heated up, expanded, and finally cooled down to its initial temperature.
Today, with significant advancements in nano-fabrication, the quantum revolution is upon us, bringing quantum heat engines into the limelight. Like their classical counterparts, quantum heat engines could be operated in various protocols which might be continuous or cyclic. Unlike classical engine which uses a macroscopic amount of the working substance, the working substance of a quantum engine has pronounced quantum features. The most prominent of these is the discreteness of the possible energies it can take. Even more outlandish from the classical point of view is the fact that a quantum system may stay in two or more of its allowed energies at the same time. This property, which has no classical analog, is known as ‘coherence’. Otherwise, a quantum Otto engine is also characterized by four strokes like its classical counterpart.
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