Power and efficiency of a thermal engine with a coherent bath

Abstract

We consider a quantum engine driven by repeated weak interactions with a heat bath of identical three-level atoms. This model was first introduced by Scully et al. [Science, 2003], who showed that coherence between the energy-degenerate ground states serves as a thermodynamic resource that allows operation of a thermal cycle with a coherence-dependent thermalisation temperature. We consider a similar engine out of the quasistatic limit and find that the ground-state coherence also determines the rate of thermalisation, therefore increasing the output power and the engine efficiency only when the thermalisation temperature is reduced; revealing a more nuanced perspective of coherence as a resource. This allows us to optimise the output power by adjusting the coherence and relative stroke durations.

Spin quantum heat engines with shortcuts to adiabaticity

“…Therefore, we will assume τ cycle = τ 2 + τ 4 = 2τ. Finally, the definitions above are not unique and alternative measures are also present [34,68].…”

“…On the other hand, inclusion of the cost in the efficiency and power of the engine cycle is also a topic of debate where alternatives are present. One proposal in this direction is to include the cost needed to implement the CD Hamiltonian to the numerator of the efficiency [34], as opposed to subtracting it from the denominator as we did in Eq. (3).…”

“…Accordingly, many proposals to realize them can be found in the literature [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21], some of which take into account finite-time engine cycles [22][23][24][25][26]. In addition, the effects of the profound quantum nature of the QHE such as such as cooperativity [27][28][29][30][31], coherence and correlations [32][33][34] on the performance of QHEs have also been investigated. Following the demonstration of a singleion engine cycle [35], genuine QHE experiments have been reported [36] with a single spin in a nuclear magnetic resonance (NMR) set up [36,37], a cold Rb atom [38], and an nitrogen-vacancy (NV) center in diamond [39].…”

“…Moreover, we also compare the performance of an STA engine with those of the adiabatic and non-adiabatic quantum Otto cycles, and we show that the improvement provided by the CD is significant from different perspectives. The assessment of the cost of STA driving in a thermodynamical process is an ongoing debate in the literature, and the method to include the STA cost we employ throughout this work is not unique [34,56,57,[67][68][69][70]. We also briefly touch on these alternative cost evaluation methods in the present case.…”

Finite-time quantum Otto engine: Surpassing the quasistatic efficiency due to friction

“…A quantum heat engine is a cycle with thermodynamic processes, and its working fluid is a quantum system with coherence, entanglement, and discrete energy levels. Due to the development of experimental techniques, it has been realized in various ways [3][4][5][6], and various heat baths have been also considered: Coherent bath was used to exceed the Carnot efficiency, and decoherent one was introduced to find the signature of quantumness [7][8][9]. Squeezed bath [10] also allowed the efficiency to be beyond the Carnot efficiency due to the nonequilibrium resource.…”