Quantum information in heat engines

Mohammad H. Ansari, Yuli V. Nazarov

Jung Jun Park, Kang-Hwan Kim, Takahiro Sagawa +1 more

The key question of this Letter is whether work can be extracted from a heat engine by using purely quantum mechanical information. If the answer is yes, what is its mathematical formula? First, by using a bipartite memory we show that the work extractable from a heat engine is bounded not only by the free energy change and the sum of the entropy change of an individual memory but also by the change of quantum mutual information contained inside the memory. We then find that the engine can be driven by purely quantum information, expressed as the so-called quantum discord, forming a part of the quantum mutual information. To confirm it, as a physical example we present the Szilard engine containing a diatomic molecule with a semipermeable wall.

Milton Aguilar, Cüneyt Ünal, Eric Lutz

Efficiency and power are two central measures of the performance of thermal machines. We here study the power-efficiency-stability trade-off in a finite-time quantum Carnot information engine, in which an information reservoir replaces the usual cold bath of a quantum Carnot engine. We analytically evaluate mean and variance of the work output, and demonstrate that maximum efficiency can be reached at both finite work output and finite work output fluctuations. We additionally show that the relative work output fluctuations may be smaller than those of the corresponding Carnot heat engine. This result implies that the finite-time quantum Carnot information engine can be more stable than the quantum Carnot heat engine, an important property for practical applications.

Xian He, Jizhou He, Jie Zheng

Noufal Jaseem, Victor Mukherjee

We study a quantum information engine (QIE) modeled by a multiqubit working medium (WM) collectively coupled to a single thermal bath. We show that one can harness the collective effects to significantly enhance the performance of the QIE, as compared to equivalent engines lacking collective effects. We use one bit of information about the WM magnetization to extract work from the thermal bath. We analyze the work output, noise-to-signal ratio, and thermodynamic uncertainty relation (TUR), and contrast these performance metrics of a collective QIE with that of an engine whose WM qubits are coupled independently to a thermal bath. We show that in the limit of high temperatures of the thermal bath, a collective QIE always outperforms its independent counterpart. In contrast to quantum heat engines, where collective enhancement in specific heat plays a direct role in improving the performance of the engines, here the collective advantage stems from higher occupation probabilities for the higher-energy levels of the positive magnetization states, as compared to the independent case. Furthermore, we show that in the limit of high temperatures, the TUR for both the collective as well as the independent QIEs violate the standard heat engine TUR bound of 2.

T. E. Humphrey, R. Newbury, Richard P. Taylor +1 more