All Questions
Tagged with bra-ket-notation or notation
1,776 questions
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Question about Schrödinger equation with scalar and vector potentials from Sakurai
This is from page 127 of Sakurai QM:
How did they obtain this result? I understand the factor comes from the Hamilton on the LHS, but how were they able to pull out the factor out of the bra-ket like ...
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1
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133
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Scientific notation with/vs. complete integers
I got into a fight on the zsh forum over the fact that zsh uses '5.' to indicate the integer 5 but stored as a floating point number. I protested that '5.0' would be better since the trailing dot is ...
- 161
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(QM) What exactly is inner product in Dirac notation?
I'm a new learner of quantum mechanics and I have some problems about inner product in Dirac notation.
By Dirac notation, a function $f(x)$ is represented by |$f$$>$ .
According to my knowledge, $&...
1
vote
1
answer
102
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What is the meaning of this term symbol-like notation for spin states, specifically found when looking at Nitrogen-Vacancy (NV) Centers?
Some context to show what I am talking about:
University of Chicago page
Wikipedia page for NV centers
Researchgate page with a picture from an article about NV Centers
Here is an image for those ...
- 365
4
votes
1
answer
496
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Notation question about taking derivative wrt a vector
I just have a notational question about dirac notation used in a paper I tried to read a while back.
Say that $|\phi\rangle \in \mathcal{H}^A \otimes \mathcal{H}^B$ and $|i \rangle \in \mathcal{H}^A$ ...
- 576
2
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1
answer
748
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What does the notation in Sakurai's text mean?
I'm trying to understand Sakurai's explanation leading up to the projection operator, pp. 17-18 (Section 1.3.2), but I'm slightly confused by the notation. So he first says that an arbitrary ket $|\...
- 153
1
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0
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96
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Conventions in spinor-helicity formalism: are Elvang & Huang using angle brackets for left or right-handed Weyl spinors?
So, I'm reading about the spinor helicity formalism. In some references, I see angle brackets referring to left-handed (dotless) spinors. For example, Cheung writes (equation numbers in this post ...
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0
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95
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Distinguishing between the dual vector of a basis vector and a vector in the dual basis
I am reading Schutz' book on GR and finding it difficult to get a hang of the index notation.
Given a basis $\{\hat{e_i}\}$ of $V$, the dual basis $\{\tilde{e^i}\}$ is the set of dual vectors ...
- 1,775
1
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3
answers
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A strange formula in Dirac's The Principles of Quantum Mechanics
Dirac used a single $\rangle$ to represent generic quantum states, which is a habit rarely adopted by other physicists. In the 4th Chapter of his The Principles of Quantum Mechanics, Dirac seems to ...
- 31
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142
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Complex conjugate of a fermion creation operator
I am analyzing page 70 of Peskin & Schroeder concerning the complex conjugate, where in Eq. (3.145) they write the following:
\begin{equation}
\begin{split}
-i\gamma^2 \int \frac{d^3p}{(2\pi)^3} \...
- 769
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votes
1
answer
171
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Is there any standard symbol for the specific charge? [closed]
Is there a standard symbol for the specific charge ($q/m$, or $\rho_{\text{electric}}/\rho_{\text{mass}}$)? Or at least a symbol that someone has ever used in a textbook or paper.
The context for me ...
- 816
1
vote
1
answer
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What is the Infinitesimal Translation Operator in Quantum Mechanics [duplicate]
In Chapter 1, page 40 of the Sakurai's book "Modern Quantum mechanics", we come across an Infinitesimal Translation Operator:
$$\mathscr{g}(d \mathbf{x'}) \vert \mathbf{x'} \rangle = \vert \...
- 125
3
votes
1
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388
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Questions from Zettili Quantum Mechanics about Dirac notation
I have a few questions about chapter 2.3
What is free state vectors?
What means $\langle\vec{r},t|\psi\rangle$?
And about chapter 2.4
Why action of operator on bra vector we write as $\langle\phi| \...
- 91
0
votes
0
answers
79
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Matrix-index ordering for $\sigma^\mu$ vs $\bar\sigma^\mu$
In $d=4$ we can write a theory of $N$ free weyl fermions
$$
\mathcal{L} = i \bar\psi_{a}(x) \bar\sigma^{\mu} \partial_\mu\,\psi^{a}(x)
$$
with
$$
(\sigma^\mu)_{\alpha\dot\alpha} = (\mathbf{1},\sigma^i)...
- 901
11
votes
6
answers
589
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How is $\pm$ notation taught / actually used by professionals?
When using notation like $5.7 \pm 0.2$ to indicate a measurement and error, it seems like there are many standards to what this could mean. Is there a standard taught to students? Is there a standard ...
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