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For questions about matrix representations of quantum gates.
4
votes
Accepted
Matrix representation of multiple qubit gates (Hadamard transform on single wire)
Your matrix representation is incorrect. In the first case, a $\mathbf H$ gate is applied to the first qubit $A$ and an identity gate $\Bbb I$ is applied to the second qubit $B$. So the effective quan …
7
votes
Accepted
What is the matrix of the iSwap gate?
Mostly I'm confused over whether the common convention is to use +i or
-i along the anti-diagonal of the middle 2x2 block.
The former. There are two $+i$'s along the anti-diagonal of the middle …
5
votes
Accepted
What applications does the quantum gate [(i,1),(1,i)] have?
That's not the right way to look at it. In quantum mechanics, time evolutions are considered to be unitary and any unitary evolution can be written as a sequence of unitary operators $U_1, U_2, U_3,\l …
4
votes
Accepted
Nielsen & Chuang Exercise 2.3 - “Matrix representation for operator products”
Consider the linear maps $A: V\to W$ and $B: W\to X$. The composition $BA$ is a linear map from $V$ to $X$. Now, how can $\mathcal{M}(BA)$ be computed from $\mathcal{M}(B)$ and $\mathcal{M}(A)$? $\mat …
2
votes
Accepted
Projection operator on Time evolution Operator
A $9\times 9$ matrix $H$ can act on a $9$ dimensional state vector, say something like:
$$|\Psi\rangle = a_0|0\rangle + a_1|1\rangle + .... + a_8|8\rangle$$
Now, say you want to find the matrix whi …
4
votes
Accepted
Square root of CNOT and spectral decomposition of the Hadamard gate
Firstly, there's a conceptual error in your calculation of the eigenvectors.
$$\begin{bmatrix} x\\y \end{bmatrix}=\begin{bmatrix} \tfrac{1}{\sqrt{2}} &\tfrac{1}{\sqrt{2}} \\ \tfrac{1}{\sqrt{2}} & -\t …