Hybrid Microwave-Cavity Heat Engine

Abstract

We propose and analyze the use of hybrid microwave cavities as quantum heat engines. A possible realization consists of two macroscopically separated quantum dot conductors coupled capacitively to the fundamental mode of a microwave cavity. We demonstrate that an electrical current can be induced in one conductor through cavity-mediated processes by heating up the other conductor. The heat engine can reach Carnot efficiency with optimal conversion of heat to work. When the system delivers the maximum power, the efficiency can be a large fraction of the Carnot efficiency. The heat engine functions even with moderate electronic relaxation and dephasing in the quantum dots. We provide detailed estimates for the electrical current and output power using realistic parameters. Introduction.-Hybrid quantum systems that couple electronic transport in nano-scale conductors to photons in microwave cavities are currently going through a remarkable and rapid development. Several recent experiments have demonstrated controllable coupling of quantum dots to the fundamental mode of a microwave cavity [1][2][3][4][5][6][7][8][9]. These experimental advances are now paving the way for a broad spectrum of applications, ranging from hybrid quantum information processing [10] and Cooper pair splitters [11] to on-chip micro-masers [12] and quantum dot lasers [13]. The ability to indirectly couple mesoscopic conductors over macroscopic distances via a microwave cavity [6], serving as a robust quantum bus for quantized energy and information flow, opens several intriguing avenues for the use of non-local electronic correlations mediated by cavity photons [14][15][16][17][18][19].

Thermoelectric energy harvesting with quantum dots

“…Only recently has the investigation of thermoelectric effects in quantum-dot structures in three-terminal geometries generated a lot of attention [44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59]. This was motivated by a number of reasons.…”

“…Finally, we will discuss heat engines driven by photons. These photons can either be absorbed from the electromagnetic environment [56] or be specifically emitted by the hot source into a resonant superconducting microwave cavity that serves as a quantum bus for heat exchanged between spatially separated mesoscopic conductors [57].…”

“…figure 1. This becomes most pronounced in a recently proposed microwave-cavity heat engine where two mesoscopic conductors such as double quantum dots are connected via a superconducting microwave cavity over a typical length of a few centimeters [57]. The separation of hot and cold baths helps to reduce leakage heat currents that are detrimental to achieving a high efficiency of heat to work conversion.…”

Principle of minimal work fluctuations

“…In particular, advances in our knowledge of thermodynamics applied to small systems have simulated studies of efficient energy devices (classical or quantum) at the microscale and nanoscale [9][10][11]. In these devices the work fluctuations are shown to be significant and the suppression of the work fluctuations is seen to be related to the heat-to-work conversion efficiency [8,12,13].…”

Suppression of work fluctuations by optimal control: An approach based on Jarzynski's equality

“…Of particular interest here is that several designs of microscale or nanoscale heat engines have been proposed theoretically [5][6][7]. For this type of applications where heat-to-work conversion efficiency and the power of work output are apparently crucial, the stability or reliability of work output also becomes an important performance indicator [8,9].…”