A "Square-root" Method for the Density Matrix and its Applications to Lindblad Operators

Abstract

The evolution of open systems, subject to both Hamiltonian and dissipative forces, is studied by writing the $nm$ element of the time ($t$) dependent density matrix in the form \ber ρ_{nm}(t)&=& \frac {1}{A} \sum_{α=1}^A γ^α_n (t)γ^{α*}_m (t) \enr The so called "square root factors", the $\gamma (t)$'s, are non-square matrices and are averaged over $A$ systems ($\alpha$) of the ensemble. This square-root description is exact. Evolution equations are then postulated for the $\gamma (t)$ factors, such as to reduce to the Lindblad-type evolution equations for the diagonal terms in the density matrix. For the off-diagonal terms they differ from the Lindblad-equations. The "square root factors" $\gamma (t)$ are not unique and the equations for the $\gamma (t)$'s depend on the specific representation chosen. Two criteria can be suggested for fixing the choice of $\gamma (t)$'s one is simplicity of the resulting equations and the other has to do with the reduction of the difference between the $\gamma (t)$ formalism and the Lindblad-equations.

arXiv comment36 pages, 7 figures

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Cited by in corpus (3)

• The wave operator representation of quantum and classical dynamics
• Non-stochastic matrix Schrödinger equation for open systems
• Positivity Preserving Density Matrix Minimization at Finite Temperatures via Square Root