All Questions
11
questions
1
vote
2
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1k
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Tensor Product vs Direct Product in QM
Consider adding angular momentum. Shankar describes the state of the system as the direct product of states while Ballentine (and I think most other people) describes the state of the system as the ...
- 69
4
votes
1
answer
330
views
The name of the Hilbert space in quantum mechanics
I know that states in quantum mechanics are positive trace class operators acting on a separable complex Hilbert space $\mathcal H$ and having trace = 1. Specifically, pure states are one-dimensional ...
- 745
6
votes
1
answer
545
views
Definition of the $S$-Matrix in Schwartz QFT-Book: Why is $\langle f, t_f | i, t_i \rangle$ in the Schroedinger picture, and not Heisenberg-picture?
On page 51, (equation 5.1), Mathew Schwartz introduces the $S$-matrix as
\begin{align}
\langle f| S | i \rangle_{Heisenberg} = \langle f, \infty | i, -\infty \rangle_{Schrödinger}
\end{align}
Were $|i,...
- 6,763
1
vote
2
answers
576
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Clarification in the difference between metastable states and excited states
The answer of this question What is the difference between metastable states and excited states?
is that the difference lie in the the time that the systems lie in a given state.
So for example take ...
- 445
0
votes
1
answer
716
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What is the difference between metastable states and excited states?
In the book Mathematical concepts of quantum mechanics ,Stephen J. Gustafson Israel,Michael Sigal, they say
The notion of a resonance is a key notion in quantum physics. It
refers to a metastable ...
- 445
5
votes
2
answers
4k
views
What does it mean when a degeneracy is lifted?
I would like to ask what is the meaning of degeneracy been lifted? For example when the Schrodinger equation is subjected to magnetic field, there is a $m\ell$ degeneracy is lifted while $\ell$ ...
2
votes
2
answers
680
views
What is a pseudopure state?
In the paper titled "Experimental Implementation of the Quantum Baker’s Map" by Weinstein et al. (Phys. Rev. Let. 89 (2002)), the author says something like
[...] the pseudopure state corresponding ...
- 2,283
3
votes
1
answer
698
views
Is a bound state a stationary state?
In Shankar's discussion on the 1D infinite square well in Principles of Quantum Mechanics (2nd edition), he made the following statement:
Now $\langle P \rangle = 0$ in any bound state for the ...
- 325
1
vote
2
answers
3k
views
Differences between eigenstates, bound states and stationary states [closed]
I am not very clear about the differences between eigenstates, bound states and stationary states.
- 27
31
votes
5
answers
12k
views
What is a state in physics?
What is a state in physics? While reading physics, I have heard many a times a "___" system is in "____" state but the definition of a state was never provided (and googling brings me totally ...
42
votes
5
answers
8k
views
Hilbert space vs. Projective Hilbert space
Hilbert space and rays:
In a very general sense, we say that quantum states of a quantum mechanical system correspond to rays in the Hilbert space $\mathcal{H}$, such that for any $c∈ℂ$ the state $\...
- 4,685