Coherent Quantum Engine

Hai Li, Xiaosong Liu, Yaming Hao

Studying the relationship between quantum coherence and energy is an intriguing and vital subject in quantum thermodynamics. Quantum engine provides an excellent platform to emphasize it. By constructing a bipartite entanglement engine (BEE) model consisting of a single qubit as the target qubit and a two-qubit as the ancilla, we have investigated the influence of quantum coherence of ancilla on work extraction of BEE at length, and analytically calculated the extractable work of BEE for the ancilla with quantum coherence (QC). We found that the extractable work of BEE is not only dependent on coherence magnitude but also related to the coherence phase of ancilla. Moreover, under certain coherent parameters, the QC can boost the work extraction from BEE. The study reveals the role of QC acting as “fuel” of engine well which deepens the understanding of the energetic effect of QC.

Brij Mohan, Rajeev Gangwar, Tanmoy Pandit +3 more

Conventional continuous quantum heat engines with incoherent heat transfer perform poorly as they exploit two-body interactions between the system and hot or cold baths, thus having limited capability to outperform their classical counterparts. We introduce distinct continuous quantum heat engines that utilize coherent heat transfer with baths, yielding genuine quantum enhancement in performance. These coherent engines consist of one qutrit system and two photonic baths and enable coherent heat transfer via two-photon transitions involving three-body interactions between the system and hot and cold baths. We demonstrate that coherent engines deliver significantly higher power output with much greater reliability, i.e., lower signal-to-noise ratio of the power, by hundreds of folds over their incoherent counterparts. Importantly, coherent engines can operate close to or at the maximal achievable reliability allowed by the quantum thermodynamic uncertainty relation. Moreover, coherent engines manifest more nonclassical features than incoherent engines because they violate the classical thermodynamic uncertainty relation by a greater amount and for a wider range of parameters. These genuine enhancements in the performance of coherent engines are directly attributed to their capacity to harness higher energetic coherence for the resonant driving case. The experimental feasibility of coherent engines and the improved understanding of how quantum properties can enhance performance may find applications in quantum enabled technologies.

Patrice A. Camati, Jonas F. G. Santos, Roberto M. Serra

The working substance fueling a quantum heat engine may contain coherence in its energy basis, depending on the dynamics of the engine cycle. In some models of quantum Otto heat engines, energy coherence has been associated with entropy production and quantum friction. We considered a quantum Otto heat engine operating at finite time. Coherence is generated and the working substance does not reach thermal equilibrium after interacting with the hot heat reservoir, leaving the working substance in a state with residual energy coherence. We observe an interferencelike effect between the residual coherence (after the incomplete thermalization) and the coherence generated in the subsequent finite-time stroke. We introduce analytical expressions highlighting the role of coherence and examine how this dynamical interference effect influences the engine performance. Additionally, in this scenario in which coherence is present along the cycle, we argue that the careful tuning of the cycle parameters may exploit this interference effect and make coherence acts like a dynamical quantum lubricant. To illustrate this, we numerically consider an experimentally feasible example and compare the engine performance to the performance of a similar engine where the residual coherence is completely erased, ruling out the dynamical interference effect.