Postulate 4:composition Composition:The state of the joint system (Si,S2),where S1 is in stateψ〉andS2in lp2),islψ1〉☒lψ2）. ☒：tensor product of vectors. -(a1,a2)☒(b1,b2,b3)=(a1b1,a1b2,a1b3,a2b1,a2b2,a2b3). -dim(lw1〉⑧lψ2)=dim(ψ1)·dim(lψ2) - size(lψ1〉⑧l2)=size(lψ1)+size(lψ2) size:number of qubits. 、Notation:l0)8n=l0〉☒…☒l0),n times.Postulate 4: composition • Composition: The state of the joint system (𝑆1, 𝑆2), where 𝑆1 is in state 𝜓1 and 𝑆2 in 𝜓2 , is 𝜓1 ⊗ 𝜓2 . • ⊗: tensor product of vectors. – 𝑎1, 𝑎2 ⊗ 𝑏1, 𝑏2, 𝑏3 = (𝑎1𝑏1, 𝑎1𝑏2, 𝑎1𝑏3, 𝑎2𝑏1, 𝑎2𝑏2, 𝑎2𝑏3). – dim 𝜓1 ⊗ 𝜓2 = dim 𝜓1 ⋅ dim 𝜓2 – size 𝜓1 ⊗ 𝜓2 = size 𝜓1 + size 𝜓2 • size: number of qubits. • Notation: 0 ⊗𝑛 = 0 ⊗ ⋯ ⊗ 0 , 𝑛 times