# Questions tagged [kraus-representation]

For questions relating to the Kraus decomposition of quantum channels.

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### Is a quantum channel reversible if all Kraus operators are proportional to unitaries?

In preskill's online lecture p.13, he stated that if a channel is reversible, i.e., $\varepsilon^{-1}\circ\varepsilon(\rho)=\rho$ for any $\rho$, then the kraus operator of the quantum channel must be ...
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### Choi matrix in QETLAB

I am using QETLAB, a package for working with quantum information theory in Matlab and I have some doubts. I am trying to calculate diamond norms using such for some quantum channels. However, when ...
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I am referring to Nielsen and Chuang Quantum Computation and Quantum Information 10th Anniversary Edition Textbook, Chapter 8.3. A linear operator $E_i:H_{QR}\longrightarrow H_Q$ is defined by: $$... 1answer 205 views ### How does qiskit finally implement a noise model? I have been reading qiskit documentation for hours and I still don't get how does it implements noise in the circuit. I have understood that it works with a objects of the class QuantumError which ... 0answers 41 views ### How is I(\rho^{QC})=I_{CC}(\rho^{QC}) On page 3 of this paper, for the proof of theorem 1, it states that, using Lemma 2 from the previous page, that if$$I(\Lambda_{A}\otimes\Gamma_{B})[\rho]=I(\rho))$$then there exists \Lambda_{A}^{*}... 0answers 46 views ### Qiskit function phase_amplitude_damping_error I am reading about the noise models that can be simulated in Qiskit and I found out the phase_amplitude_damping_error function. I read about it and it seems to be a function that simulates a combined ... 0answers 140 views ### Affine Map of the Bloch sphere I am referring to Equation (8.89) to (8.92) in Chapter 8 of "Quantum Computing and Information 10th Anniversary Edition" by Nielsen and Chuang. This section deals with the geometric picture of single ... 1answer 86 views ### Derivation of Equation 8.7 in Nielsen Chuang [duplicate] Equation \eqref{eq:sp1} represents the reduced state of the system after tracing over environment.(Page number 358)$$\mathcal{E}(\rho) = \mathrm{tr}_{env}(\lbrack U(\rho \otimes \rho_{env} )U^{\...
As discussed in Watrous' book, quantum-to-classical channels are CPTP maps whose output is always fully depolarised. These can always be written as \Phi_\mu(X) = \sum_a \langle X,\mu(a)\rangle E_{a,...