Is x^kp_x^m Hermitian?

In summary, the operator x^kp_x^m is not hermitian, whereas \frac{x^kp_x^m+p_x^mx^k}{2} is. To prove this, one needs to conjugate the integrand and all terms in the operator.
  • #1
KBriggs
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Homework Statement


Show that the operator [tex]x^kp_x^m[/tex] is not hermitian, whereas [tex]\frac{x^kp_x^m+p_x^mx^k}{2}[/tex] is, where k and m are positive integers.




The Attempt at a Solution



Is this valid?

[tex]<x^kp_x^m>^*=\left(\int_{-\infty}^\infty\Psi^*x^k(-i\hbar)^m\frac{\partial^m\Psi}{\partial x^m} dx\right)^*[/tex]
[tex]=\int_{-\infty}^\infty\Psi^*(i\hbar)^m\frac{\partial^m(x^k\Psi^*)}{\partial x^m} dx \neq <x^kp_x^m>[/tex]

That is, can you conjugate an integral by conjugating its integrand? Can you conjugate a derivitive by conjugating the function you are differentiating?

And assuming that you can, did I carry out the conjugation correctly?
 
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  • #2
You can conjugate the integrand, however, you have to conjugate all of the terms. Basically what happens is that the bra and the ket switch, and the operator is conjugated.

[tex]\langle \phi | A | \psi \rangle^* = \langle \psi | A^* | \phi \rangle[/tex]
 

What is a valid Hermitian operator?

A valid Hermitian operator is a mathematical operator that has the property of being self-adjoint, meaning that it is equal to its own adjoint. In other words, when the operator is applied to a vector, the resulting vector is the same as when the adjoint of the operator is applied to the vector.

What is the significance of a Hermitian operator being valid?

A valid Hermitian operator is important because it allows us to perform mathematical operations on quantum systems, which are governed by the laws of quantum mechanics. These operators play a crucial role in determining the properties and behavior of quantum systems.

How do you determine if an operator is Hermitian?

To determine if an operator is Hermitian, you can use the Hermitian conjugate (or adjoint) rule. This rule states that if an operator is Hermitian, then its conjugate is equal to its transpose. In mathematical terms, this can be written as A† = A where A is the Hermitian operator and A† is its adjoint.

Can a non-square matrix be a valid Hermitian operator?

No, a non-square matrix cannot be a valid Hermitian operator. In order for an operator to be Hermitian, it must have the same number of rows and columns, meaning it must be a square matrix. This is necessary in order for the operator to have an adjoint that is also a matrix.

What are some real-world applications of Hermitian operators?

Hermitian operators have various applications in quantum mechanics, such as in determining the energy states of a quantum system and predicting the outcomes of quantum measurements. They are also used in signal processing and image processing, as well as in engineering and physics for solving differential equations and modeling physical systems.

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