Why do the degrees of freedom of a density operator not match up with the degrees of freedom of a state vector?
75803
Why does the space of pure qudit states have dimension $2(D-1)$, rather than $D^2-2$?
113275
How to find the reduced density matrix of a four-qubit system?
14867
How to interpret $\langle x|\hat Q|x'\rangle$ for a quantum mechanical operator $\hat Q$?
44843
What is the difference between $|0\rangle $ and $0$?
11181
Counting degrees of freedom of gauge bosons
155176
Tensor product vs. Cartesian Product for composite quantum systems
138832
Expansion coefficients of an arbitrary state in the Hilbert space of one-particle states
92744
These two operators commute...but their eigenvectors aren't all the same. Why?
16159
In counting degrees of freedom of a linear molecule, why is rotation about the axis not counted?
71626
Superposition of distinct vevs in spontaneous symmetry breaking
54548
Expectation value for $\frac{1}{r}$ in the $|nlm\rangle$ state of hydrogen
45244
Why the statement "there exist at least one bound state for negative/attractive potential" doesn't hold for 3D case?
131091
Srednicki's Path Integrals: Ground-State to Ground-State Transition Amplitude in the Presence of a Perturbation
108464
Necessary and sufficient conditions for a function to be the Wigner function of state
90250
Two explanations of non-zero atomic radius
41470
Is the density operator a mathematical convenience or a 'fundamental' aspect of quantum mechanics?
18564
Why is the symmetry variation $\delta_s q$ different from the ordinary variation $\delta q$?