Is there any way to see that $H= p^2 +x^2$ has level-spaced spectrum from the symmetry?
54197
Why are the energy levels of a simple harmonic oscillator equally spaced?
141907
Haag's theorem and practical QFT computations
30923
Is the matrix $A^*A$ and $AA^*$ hermitian?
78075
Why can I apply $HS^\dagger$ and then measure in the computational basis to measure $Y$?
69031
Square of angular momentum operator in spherical coordinates
12698
Orthonormal basis for $\mathcal{L}^2([0,1])$
44747
Finding the effective Hamiltonian in a certain subspace
68153
How to show that $L^p$ spaces are nested?
45626
How do I calculate the eigenvalues of the positive partial transpose of this two-qubit state?
14867
How to interpret $\langle x|\hat Q|x'\rangle$ for a quantum mechanical operator $\hat Q$?
20978
How do we know that we have captured the entire spectrum of the Harmonic Oscillator by using ladder operators?
127799
Eigenvalues of symmetric matrices are real without (!) complex numbers
20025
Fourier transform of $\exp(-t^2)$ using contour integration.
118134
If $\psi h$ is in $L^2$ for all $h\in L^2$, must $\psi$ be essentially bounded?
133609
orthonormal system in a Hilbert space
67106
Projection on the hyperplane $H: \sum x_i=0$
106803
How to see $\cos x \leq \exp(-x^2/2)$ on $x \in [0,\pi/2]$?