Hermitian Operators: Meaning & Showing Properties

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    Hermitian Operators
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Discussion Overview

The discussion focuses on the concept of Hermitian operators in the context of quantum mechanics, specifically exploring their definitions and properties. Participants seek to understand what it means for an operator to be Hermitian and how to demonstrate that certain combinations of operators are Hermitian.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant defines a Hermitian operator as one that is included in its adjoint, suggesting that the definition involves the relationship \( A \subseteq A^{\dagger} \).
  • Another participant questions the formulation of the second part of the question, indicating that it lacks clarity regarding the domains of the operators and suggests assuming the operators are bounded.
  • A different participant mentions that in quantum mechanics, one typically assumes a basis for operators and discusses how to analyze the transformation of matrix elements to prove Hermiticity.
  • Some participants express confusion about how to approach the second question, particularly regarding the demonstration that \( O + O' \) is Hermitian, with one noting that \( O' = O \).
  • One participant provides a mathematical expression involving adjoints to suggest a way to approach the problem, indicating that \( (O + O^{\dagger})^{\dagger} \) relates to \( O^{\dagger} + O \).

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the clarity of the questions posed or the approach to demonstrating the properties of Hermitian operators. There are multiple viewpoints on how to interpret the definitions and the implications of the operators' domains.

Contextual Notes

Some limitations noted include the lack of clarity regarding the domains of the operators involved and the assumptions necessary for the operators to be considered bounded.

sunsun
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1.What does it mean for an operator to be hermitian?

Note: the dagger is represented by a '
2. How do I show that for any operator ie/ O' that O + O' , i(O-O') and OO' are hermitian?

Thanks in advanced
 
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It means to be included in its adjoint. By definition

[tex]A\subseteq A^{\dagger} \ \mbox{means that A is hermitian/symmetric} [/itex]<br /> <br /> As for the second part, I'm sure the question is ill posed, as there's no mentioning of domains for the operators. you can simplify it by assuming the involved operators are bounded, hence defined on all the Hilbert space.[/tex]
 
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Typically in a quantum mechanics course, you can assume a basis for your operators that they will span. To prove that the above operators are Hermitian, you'd want to look at how the matrix elements transform:

[tex]\langle n | \left ( \mathcal{O} | m \rangle \right ) = \left ( \langle n | \mathcal{O}^\dagger \right ) | m \rangle = \langle m | \left ( \mathcal{O}| n \rangle \right ) ^*[/tex]
by definition. But if [tex]\mathcal{O}^\dagger = \mathcal{O}[/tex], what does that mean about the matrix elements?
 
Im sorry, I don't really get that.

How would I go around starting to answer the Q2? I know that O' = O
But how would I show that O+O' is hermitian?
 
sunsun said:
Im sorry, I don't really get that.

How would I go around starting to answer the Q2? I know that O' = O
But how would I show that O+O' is hermitian?

I'll let you figure out the domain issues, but

[tex](O+O^{\dagger})^{\dagger}\supseteq O^{\dagger}+O^{\dagger\dagger} \supseteq O^{\dagger}+O[/tex] ,

since [itex]O\subseteq O^{\dagger\dagger}[/itex]
 

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