# 问题：

Show that the tensor product of two positive operators is positive.

## 解答

$A \otimes B=\left(U [\Lambda] U^{\dagger}\right) \otimes\left(U^{\prime} [\Lambda^{\prime}] U^{\prime}\right)=\left(U \otimes U^{\prime}\right)\left([\Lambda] \otimes [\Lambda^{\prime}]\right)\left(U^{\dagger} \otimes U^{\prime}\right)$；

#### 参考

[1]www.qtumist.com