Open-System Derivations

Open-system derivations are especially assumption-sensitive. Track which environment is traced out, whether the dynamics is Markovian, and whether a master equation is exact or approximate.

Channels and Operations

• Kraus Map
• POVMs: First Encounter
• Generalized Measurements Overview
• Partial Trace
• Density Operators

Master Equations

• Lindblad Equation
• Lindblad Generator Hamiltonian Card
• von Neumann Entropy
• Density Matrix Expectation

Decoherence and Measurement

• Decoherence Preview
• Classical Limit
• State Update Rule
• What Measurement Formalism Does Not Settle

Reading Cautions

Do not infer a Lindblad equation merely from the existence of an environment. Common derivations use weak coupling, separation of time scales, coarse graining, secular approximations, or semigroup assumptions. The compact Reference cards should be read with those assumptions visible.

References

• H.-P. Breuer and F. Petruccione, The Theory of Open Quantum Systems, Oxford University Press, 2002.
• H. M. Wiseman and G. J. Milburn, Quantum Measurement and Control, Cambridge University Press, 2010.
• J. Watrous, The Theory of Quantum Information, Cambridge University Press, 2018.