Is the Hermite Conjugate Needed for Expectation Values of Spin?

In summary, the conversation discusses the expectation value for S_x (spin in x-direction) and the use of hermite conjugate in calculating it. The question is raised about whether complex conjugate should be used instead. The answer clarifies that by definition, they are essentially the same thing.
  • #1
Niles
1,866
0

Homework Statement


Hi all.

The expectation value for S_x (spin in x-direction) is:

[tex]
\left\langle {S_x } \right\rangle = \left\langle {\phi |S_x \phi } \right\rangle = \phi ^\dag S_x \phi
[/tex]
where \phi is the state and \phi^"sword" is the hermite conjugate.

My question is: I thought that when finding expectation values, you are supposed to complex conjugate the left part of the inner product, not hermite conjugate?
 
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  • #2
I am fairly certain that by definition,

[tex](S^T)^*=S^{\dag}[/tex]

so in a way it's the same thing (T is the transpose matrix)
 
  • #3
I get it - thanks :-)
 

FAQ: Is the Hermite Conjugate Needed for Expectation Values of Spin?

What is the concept of "expectation values" in QM?

In quantum mechanics, expectation values refer to the average value of a physical quantity that is predicted by a particular quantum state. It is calculated by taking the weighted average of all possible values of the quantity, with the weights determined by the probability amplitudes of the quantum state.

How do you calculate the expectation value of spin in QM?

The expectation value of spin in QM is calculated by taking the inner product of the quantum state with the spin operator. This involves summing the products of the spin values and their respective probabilities. The resulting expectation value gives the average spin value that would be measured if the experiment were repeated multiple times.

What is the significance of expectation values in QM?

Expectation values play an important role in QM as they provide a way to connect the abstract mathematical formalism of the theory to measurable physical quantities. They also allow for predictions to be made about the outcomes of experiments and can be used to analyze the behavior of quantum systems.

How are expectation values of spin related to quantum states?

The expectation values of spin are closely related to quantum states, as they are calculated using the quantum state. Different quantum states can have different expectation values, which can provide valuable information about the properties and behavior of the system described by the state.

Can the expectation value of spin be measured in experiments?

Yes, the expectation value of spin can be measured in experiments. This is done by performing multiple measurements on identical quantum systems in the same quantum state and calculating the average spin value. The closer the measured spin values are to the expectation value, the more accurate the predictions of QM are.

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