Expectation value calculation

In summary, the purpose of calculating the expectation value is to determine the average value or outcome of a specific measurement in a system. The expectation value is calculated by multiplying the value of each possible outcome by its corresponding probability and summing up all of these products. This concept is significant in quantum mechanics as it is used to describe the average value of a physical quantity in a quantum state. The expectation value can be negative and is related to uncertainty through the Heisenberg uncertainty principle.
  • #1
ertansinan
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0
How can we compute the expectation value, <[itex]\widehat{x}[/itex][itex]\widehat{p}[/itex]> where ψ(x) is a normalized wavefunction? (The result is i[itex]\hbar[/itex]/2)
 
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  • #2
If you want to do the calculation in x-space you have to use the momentum operator represented by [itex]-i\hbar\partial_x[/itex]; then you get the integral

[tex]\langle\psi|\hat{x}\hat{p}|\psi\rangle = \int_\mathbb{R}dx\,\psi^\ast(x)\,x\,(-i\hbar)\,\partial_x\,\psi(x)[/tex]

Note that your result [itex]i\hbar/2[/itex] cannot be correct in general.
 

1. What is the purpose of calculating the expectation value?

The expectation value is calculated to determine the average value or outcome of a specific measurement in a system. It allows scientists to make predictions and draw conclusions about the behavior of a system based on its underlying properties.

2. How is the expectation value calculated?

The expectation value is calculated by multiplying the value of each possible outcome by its corresponding probability, and then summing up all of these products. This can be represented mathematically as E[x] = Σ xP(x), where x is the possible outcomes and P(x) is the probability of each outcome.

3. What is the significance of the expectation value in quantum mechanics?

In quantum mechanics, the expectation value is used to describe the average value of a physical quantity in a quantum state. It is a fundamental concept in quantum mechanics and is used to make predictions about the behavior of particles and systems at the microscopic level.

4. Can the expectation value be negative?

Yes, the expectation value can be negative. This can occur when the possible outcomes have both positive and negative values and the corresponding probabilities are such that the negative values have a higher likelihood of occurring.

5. How is the expectation value related to uncertainty?

The expectation value is related to uncertainty through the Heisenberg uncertainty principle, which states that the more precisely one property of a particle is measured, the less precisely the other property can be known. In other words, the more certain we are about the expectation value of one property, the less certain we can be about the expectation value of another property.

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