Molecular Heat Engines: Quantum Coherence Effects

Abstract

Recent developments in nanoscale experimental techniques made it possible to utilize single molecule junctions as devices for electronics and energy transfer with quantum coherence playing an important role in their thermoelectric characteristics. Theoretical studies on the efficiency of nanoscale devices usually employ rate (Pauli) equations, which do not account for quantum coherence. Therefore, the question whether quantum coherence could improve the efficiency of a molecular device cannot be fully addressed within such considerations. Here, we employ a nonequilibrium Green function approach to study the effects of quantum coherence and dephasing on the thermoelectric performance of molecular heat engines. Within a generic bichromophoric donor-bridge-acceptor junction model, we show that quantum coherence may increase efficiency compared to quasi-classical (rate equation) predictions and that pure dephasing and dissipation destroy this effect.

Optomechanical heat transfer between molecules in a nanoplasmonic cavity

“…Achieving thermal control of molecular systems is a topic of current interest in various fields, such as quantum thermodynamics, quantum biology and quantum chemistry [1][2][3][4][5][6][7][8]. In order to achieve this, it is necessary to gain a fundamental understanding of the transfer of heat, and energy in general, between molecules.…”

Numerically exact full counting statistics of the energy current in the Kondo regime

“…40 However, there is no comprehensive answer to the question of whether quantum effects improve or reduce the performance of nonlinear heat engines at the nanoscale. In certain specific cases, quantum coherence effects have been shown to increase arXiv:1907.09546v1 [cond-mat.mes-hall] 22 Jul 2019 the thermal efficiency, 41 to exceed the Carnot efficiency and approach a perfect efficiency of 1, 42 to increase the power output 43 and to reduce fluctuations in the power. 44 Whereas it is possible to study nanoscale thermoelectricity within a single-particle approximation with Green's function [45][46][47] or DFT-based [48][49][50] methods, the effect of Kondo physics on the thermoelectric performance of devices is not fully understood beyond linear response.…”

Absence of Coulomb Blockade in the Anderson Impurity Model at the Symmetric Point

“…In recent years, numerous approximate methods have been developed to study transport through nanoscale interacting systems. Among these are quantum master equation approaches and their generalizations, [10][11][12][13][14][15][16] approaches based on the nonequilibrium Green's function formalism, [17][18][19][20][21][22][23][24] and quasi-classical mapping techniques. 25,26 More recently, numerically exact approaches (namely, methods that allow for a systematic convergence of the results) have been proposed that allow for an assessment of the approximate methods in certain regimes of interactions and temperatures.…”