Going Beyond the Carnot Limit with a quantum Otto engine

Researchers have shown that the effi ciency at maximum power of a quantum Otto engine can be dramatically enhanced by coupling it to a squeezed thermal reservoir. While standard heat engines interact with thermal baths which are only characterized by their respective temperatures, the use of nonthermal baths o ffers more degrees of control and manipulation, such as the amount of squeezing, that can be exploited to increase the work produced. Their findings pave the way for a first experimental demonstration of the usefulness of reservoir and state engineering techniques in quantum thermodynamics and the realization of more e fficient nano-engines.

E fficiency at maximum power given by the generalized Curzon-Ahlborn effi ciency as a function of the squeezing parameter r (red line). The region below the red dashed line corresponds to all possible e fficiencies in agreement with the standard Carnot limit. The results of the Monte-Carlo simulations (black dots) demonstrate within the given trap geometry that by squeezing the thermal state with the effi ciency can be increased by a factor of four, which is two times higher than the corresponding Carnot bound. The black dotted line shows the generalized Carnot limit for an engine interacting with a hot squeezed thermal bath. The results shown are performed at a temperature ratio of 0.88.

Arxiv – Nanoscale Heat Engine Beyond the Carnot Limit (6 pages)

Physical Review Letters – Nanoscale Heat Engine Beyond the Carnot Limit

We consider a quantum Otto cycle for a time-dependent harmonic oscillator coupled to a squeezed thermal reservoir. We show that the efficiency at maximum power increases with the degree of squeezing, surpassing the standard Carnot limit and approaching unity exponentially for large squeezing parameters. We further propose an experimental scheme to implement such a model system by using a single trapped ion in a linear Paul trap with special geometry. Our analytical investigations are supported by Monte Carlo simulations that demonstrate the feasibility of our proposal. For realistic trap parameters, an increase of the efficiency at maximum power of up to a factor of 4 is reached, largely exceeding the Carnot bound.

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