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Bath generated work extraction and inversion-free gain in two-level systems

A. E. Allahverdyan·Th. M. Nieuwenhuizen
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Abstract

The spin-boson model, often used in NMR and ESR physics, quantum optics and spintronics, is considered in a solvable limit to model a spin one-half particle interacting with a bosonic thermal bath. By applying external pulses to a non-equilibrium initial state of the spin, work can be extracted from the thermalized bath. It occurs on the timescale $\T_2$ inherent to transversal (`quantum') fluctuations. The work (partly) arises from heat given off by the surrounding bath, while the spin entropy remains constant during a pulse. This presents a violation of the Clausius inequality and the Thomson formulation of the second law (cycles cost work) for the two-level system. Starting from a fully disordered state, coherence can be induced by employing the bath. Due to this, a gain from a positive-temperature (inversion-free) two-level system is shown to be possible.

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A. E. Allahverdyan, Th. M. Nieuwenhuizen. 2002-01-23. Bath generated work extraction and inversion-free gain in two-level systems. https://doi.org/10.1088/0305-4470%2F36%2F4%2F301

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