A mixture of states is an convex combination of states, i.e.

ρ = ∑_jp_jρ_j
where

∑_jp_j = 1
and the p_j ≥ 0 are real.

Physically this corresponds having state ρ_j with probability p_j.

All mixed states can be written as a mixture of pure states.

See also

• Mixed state
• Pseudomixture

Category:Quantum States Category:Mathematical Structure