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

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 T2 inherent to quantum coherence. The work (partly) arises from heat given off by the surrounding bath, while the spin entropy remains constant during a pulse. This presents a new mechanism and time and temperature regimes for limiting the validity of the Clausius inequality and Thomson's formulation of the second law (cycles cost work). Apart from this, starting from a fully disordered state, coherence can be induced by employing the bath. A gain from a positive-temperature (inversion-free) two-level system is shown to be possible