We investigate the energetic and thermodynamic performance of an interacting two-qubit system serving as both a quantum battery and a quantum Otto heat engine. The working medium is described by an anisotropic Heisenberg Hamiltonian supplemented by a dipolar interaction, a symmetric spin--orbit interaction, and an external magnetic field. Within a unified microscopic framework, we first analyze a coherent unitary charging protocol and characterize the resulting energy-storage performance through the ergotropy, anti-ergotropy, charging power, storage capacity, and
ℓ1-norm of quantum coherence. We investigate the effects of the dipolar interaction, temperature, and magnetic field on these quantities. We then employ the same working medium in a quantum Otto cycle and study the absorbed and released heat, net work, and thermodynamic efficiency as functions of the magnetic-field modulation, dipolar interaction, and temperature bias. A direct comparison between the two protocols reveals a pronounced contrast in their response to the dipolar interaction. In the investigated parameter regime, increasing the dipolar interaction substantially enhances the maximum ergotropy and storage capacity of the quantum battery, whereas the maximum work extracted per Otto cycle decreases. The Otto efficiency exhibits a nonmonotonic dependence on the dipolar interaction while remaining below the Carnot bound. These results demonstrate that an enhancement of quantum energy-storage capability does not necessarily imply an enhancement of heat-to-work conversion. Our findings highlight the complementary nature of quantum batteries and quantum heat engines and show how microscopic spin interactions can
be used to control different forms of quantum energy conversion within
the same physical platform.
We note the existence of a set of magnetic field values where a simple Hahn echo sequence refocuses the dynamics of the full dipolar interaction, for spin systems of electron donors in silicon. As the refocussing occurs for both arbitrary coupling strengths and arbitrary times, these dipolar refocusing points (DRPs) offer new possibilities for regulating entanglement due to the always-on spin dipolar interaction. While the experimental effects of DRPs will be strongly diluted in the measured coherences of thermal (unpolarized) spin ensembles, we investigate possible signatures in coherence decays arising from a study of the combined effects of decoherence arising from instantaneous diffusion and direct flip-flops
In this work we consider a bipartite system consisting of magnetic dipoles, initially characterized by product-states uncorrelated until the dynamics of evolution is established by magnetic dipole interaction. We reproduce the dynamic behavior of the entanglement produced by the magnetic dipole interaction through its temporal dependence, connection with local quantum coherences or symmetries of initial states and interaction parameters, thus establishing criteria that extremize the entanglement. We also investigated the entanglement production capacity of the magnetic dipole interaction for some classes of states with lower purities, with and without initial entanglement, thus identifying relevant aspects between purity, symmetry and necessary local quantum coherences. We show, above all, that some classes of partially entangled states can preserve or generate maximum entanglement under magnetic dipole interaction for different instants of time.