# Questions tagged [nielsen-and-chuang]

For questions about exercises or passages from the popular quantum computing textbook *Quantum Computation and Quantum Information* by Michael Nielsen and Isaac Chuang.

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### In quantum error correction, what does an "arbitrary error that yields an un-normalized state" mean?

This is from page 434 of Nielsen and Chuang: . Supposing the state of the encoded qubit is |ψ⟩ before the noise acts, then after the noise has acted the state is E(|ψ⟩⟨ψ|). To analyze the effects of ...
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### Prove that a C2(U) gate (for any single qubit unitary U) can be constructed using at most eight one-qubit gates, and six controlled- NOTs [duplicate]

Its a Problem from Michael Nielsen quantum computation and quantum information
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### What is the definition of expectation value in Nielsen and Chuang?

As someone who learned Quantum Mechanics prior to studying Quantum Computing, I am having problems with this book. For example, equation 2.92 is incorrect. That is the definition of expected value, ...
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### Copying quantum state [closed]

I'm confused about the last complete sentence in the following paragraphs. If ab=0, that means either a or b equals to 0. As a result, doesn't $|\psi\rangle|\psi\rangle$ equal to either $b^2|11\rangle$...
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### Why does $a ⊕ (a ⊕ b) = b$ and $(a ⊕ b) ⊕ b = a$? [closed]

For the following circuit that swap two qubits The sequence of gates is said to have the following sequence of effects on a computational basis state |a, b> where all additions are done modulo 2. ...
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### what are the angles 𝜃, and ϕ values of the following quantum state? [duplicate]

I need to find the coordinate 𝜃 and ϕ values of the quantum state on the bloch sphere $$\left| \varphi \right>=\frac{1+i}{\sqrt{3}} \left| 0 \right> + {\sqrt{\frac{1}{3}}} \left| 1\right>$$...
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