Extracting energy via bosonic Gaussian operations

Abstract: Quantum thermodynamics is often formulated as a theory with constrained access to operations and resources. In this manuscript, we find a closed formula for the Gaussian ergotropy, i.e. the maximum energy that can be extracted from bosonic systems governed by quadratic Hamiltonians by means of Gaussian unitaries only. This formula resembles the well-known eigenvalue-based expression for the standard ergotropy, but is instead formulated using symplectic eigenvalues. We further prove that the Gaussian ergotropy is additive, indicating that the multiple-copy scenario does not benefit from Gaussian entangling operations. Extending our analysis to the relationship between ergotropic and entropic functions, we establish bounds linking entropic measures of Gaussianity to extractable work. Finally, we generalise our framework to open systems by studying the optimal state preparation that minimises the energy output in a Gaussian channel.