# Linked Questions

3answers
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### Bra Ket Notation and Derivative [duplicate]

Let $$a$$ be the partial derivative symbol with respect to $x$. What is $$\langle x|a|x \rangle$$ equal to? I think it is 0 but not sure.
2answers
117 views

### Transformation connecting two representations - Quantum mechanics [duplicate]

I am working on Dirac's paper The Lagrangian in Quantum Mechanics. He looks for the analogy between a classical transformation between two sets of coordinates and momenta $p_r$, $q_r$ and $P_r$, $Q_r$ ...
1answer
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### Momentum operator expression

In the course of calculating $$\langle x|\hat{p}|\psi\rangle$$ I have a step which is: $$\langle x|\frac{\hbar}{i}\frac{d}{dx}|\psi\rangle=\frac{\hbar}{i}\frac{d}{dx}\langle x|\psi\rangle.$$ What is ...
4answers
266 views

I am trying to calculate $\langle x\ |\ \hat{x}\ |\ p\rangle$. I can work in the $x$-basis like so: $$\langle x\ |\ \hat{x}\ |\ p\rangle=\int dx'\langle x\ |\ \hat{x}\ |\ x'\rangle\langle x'\ |\ p\... 2answers 321 views ### Space translation of operators, states, and particle densities In Sidney Coleman's Lectures he talked about space translations such that$$\tag{1} e^{ia P}\rho(x) e^{-ia P} ~=~ \rho(x-a),$$but when I expanded the exponentials and used the commutation relation ... 2answers 374 views ### Understanding momentum space and position space I'm starting a more 'formal' course on quantum mechanics, and we're going through momentum and position space, which I'm kind of confused on. I would just like clarification on this since I'm not ... 3answers 312 views ### What's the correct link between Dirac notation and wave mechanics integrals? In wave mechanics when we compute the expectation value of energy we write the following$$\left<\hat{H}\right>=\int_{-\infty}^\infty\mathrm{d}x\ \psi^*(x)\hat{H}\psi(x)=\int_{-\infty}^\infty\...

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