Efficiency at maximum power of a discrete feedback ratchet

Abstract

Efficiency at maximum power is found to be of the same order for a feedback ratchet and for its open-loop counterpart. However, feedback increases the output power up to a factor of five. This increase in output power is due to the increase in energy input and the effective entropy reduction obtained as a consequence of feedback. Optimal efficiency at maximum power is reached for time intervals between feedback actions two orders of magnitude smaller than the characteristic time of diffusion over a ratchet period length. The efficiency is computed consistently taking into account the correlation between the control actions. We consider a feedback control protocol for a discrete feedback flashing ratchet, which works against an external load. We maximize the power output optimizing the parameters of the ratchet, the controller, and the external load. The maximum power output is found to be upper bounded, so the attainable extracted power is limited. After, we compute an upper bound for the efficiency of this isothermal feedback ratchet at maximum power output. We make this computation applying recent developments of the thermodynamics of feedback-controlled systems, which give an equation to compute the entropy reduction due to information. However, this equation requires the computation of the probability of each of the possible sequences of the controller's actions. This computation becomes involved when the sequence of the controller's actions is non-Markovian, as is the case in most feedback ratchets. We here introduce an alternative procedure to set strong bounds to the entropy reduction in order to compute its value. In this procedure the bounds are evaluated in a quasi-Markovian limit, which emerge when there are big differences between the stationary probabilities of the system states. These big differences are an effect of the potential strength, which minimizes the departures from the Markovianicity of the sequence of control actions, allowing also to minimize the departures from the optimal performance of the system. This procedure can be applied to other feedback ratchets and, more in general, to other control systems.

Fractional Quantum Heat Engine

“…The classical and quantum version of the Szilard engine has been studied in detail theoretically and experimentally [1,2,3,4,5,6,7,8,23,9,10,11,12,13,14,14,15,16,17,18,19,20,21,22,24]. These studies show that it is possible to set quantum Szilard heat engines which can extract positive work in nano-size without violate the second law of thermodynamics.…”

“…In many theoretical studies, it has been shown that the positive work and efficiency can be obtained by using quantum Sizilard engine [3,4,5,6,7,8]. On the other hand, many experimental realization have been implemented both of quantum engine and quantum Szilard engine [9,10,11,12,13,14,15,16,17,18,19,20,21,22]. Recently, a similar version of the quantum engine has been studied by Thomas et al [23] for the infinite well potential.…”

Quantum Szilard engine for the fractional power-law potentials

“…On the other hand, today, we know that both quantum engine and quantum Szilard engine were experimentally realized [7][8][9][10][11][12][32][33][34][35][36][37][38] . Therefore, we state that based on previous experimental methods and by implementing, for instance, fractal geometries or structures with porous surfaces to the experimental setup, it may possible to realize a fractional quantum heat engine in practice.…”

Relativistic quantum heat engine from uncertainty relation standpoint

“…Numerous experiments to analyze quantum engine have been explored [8,9]. Exploration of nano-scale devices like quantum ratchet [10,11], molecular motor [12] and Brownian heat engine [13,14] have enhanced the field of quantum thermodynamics.…”