# Questions tagged [matrix-elements]

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### Squared matrix elemet differs between FORM/MadGraph [on hold]

I would like to consider a process like e+ e- -> Z -> t t~ and compute the squared matrix element. My code in FORM (only the relevant pieces) is the following: ...
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### Which of the following rotation matrices best describes the transform? [closed]

Explain the following steps how could explain the point Q & p
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### How can quantum operators be expressed as a matrices?

I have just started quantum mechanics with Shankar. In my understanding, quantum operators are linear operators in infinite-dimensional Hilbert spaces. Shankar has repeatedly treated quantum ...
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### How an operator is converted to a function? [closed]

$$\langle m|F|n\rangle^*=\langle F(n)|m\rangle$$ How does the operator become a function of state $|n\rangle$?
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### Levi-Civita tensor

The Kronecker delta can be represented by a two dimensional matrix: \begin{gather} \delta_{ij}=\mathbb{I}= \begin{bmatrix} 1&0&0\\ 0&1&0\\ 0&0&1\\ \end{bmatrix}. \end{gather} ...
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### Using Dirac notation to find matrix representation

I am currently reading Sakuria, and I cannot get my head around how one uses the completeness relation to derive the matrix representations of outer products. In the first chapter he states that an ...
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### How to derive the Schrödinger Equation from Heisenberg's matrix mechanics and vice-versa?

How do you derive the Schrödinger equation (wave mechanics, time dependent state) from Heisenberg's Matrix Mechanics (matrix based, time dependent operators)
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### Proof that elastance matrix is invertible

I was reading this lecture notes from MIT OCW on capacitance . It says $V_i =\sum_j P_{ij}Q_{j}$ where the constants $P_{ij}$ are determined by the geometry of the conductors. This matrix can ...
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### using symmetry in the siffness method

Good day All while trying to solve this exercice I tried to find a symmetry plan to make my computations easy and according to my basic understanding the symmetry must be in term of: lenght length ...
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### How is simple matrix representation related to quantum probabilities?

I went again through some of my undergraduate books of quantum mechanics to get a new look at it as a futur PhD (not in QM though). I got answers for some old questions that bugged me at the time but ...
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### truncation before matrix exponential: how to do it right?

I'm trying to compute (numerically) the matrices of some simple quantum optical operations, which in principle are unitary. However, in my case they are unitary in an infinite-dimensional space, so I ...
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### Finding the eigenvalues and eigenvectors of this operator

The operator $$\mathcal{\hat{G}} = (\xi - 1) \sum_{j=1}^N \int dk_j \; k_j \hat{a}^\dagger_j(k_j)\hat{a}_j(k_j),$$ is physically similar to the momentum operator in quantum mechanics. It has the ...