# Questions tagged [quantum-operation]

For questions about completely positive (CP) linear maps between quantum states. Can also be used for trace-preserving CP maps (quantum channels). For questions about unitary operations, please use quantum-gate instead.

241 questions
Filter by
Sorted by
Tagged with
212 views

218 views

### Why does a quantum operation being trace-preserving imply that $\sum_k E_k^\dagger E_k=I$?

I am reading Nielsen Chuang Chapter 8. They say that if a quantum operation is trace-preserving, then $$Tr\left(\sum_k E_k^{\dagger}E_k \rho\right) = 1$$ which I understand....
61 views

### SWAP test and density matrix distinguishability

Let us either be given the density matrix $$|\psi\rangle\langle \psi| \otimes |\psi\rangle\langle \psi| ,$$ for an $n$ qubit pure state $|\psi \rangle$ or the maximally ...
44 views

64 views

### What is a covariant quantum channel?

A novice to this topic, I am trying to understand the notion of (irreducible) Covariant Quantum Channels. This article provides a definition that is not very "physical". My question: What ...
53 views

164 views

69 views

### Equivalent statement of the unitary freedom of Kraus operator?

There is a well-known form of the unitary freedom of Kraus operators, which can be found in Nielsen's book, stating that two sets of Kraus operators describe the same physical process of the system(...