The Heisenberg-Langevin equations are equations for open quantum systems. They are a specific case of Quantum Langevin equations. In the Heisenberg picture the time evolution of a quantum system is the operators themselves. The solution to the Heisenberg equation of motion determines the subsequent time evolution of the operators. The Heisenberg-Langevin equation is the generalization of this to open quantum systems.
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Heisenberg-Langevin equation Wikipedia(Text) CC BY-SA