Is the Rotation of Spherical Harmonics Using Wigner Matrices Correct?

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Homework Statement
Rotate the spherical harmonic $$\ket{l=2, m=1}=Y_{2, 1}$$ an angle of π/4 about the y-axis.
Relevant Equations
$$\sum_{m'=-l}^{l} {d^{(l)}}_{m, m'} Y_{l, m'}$$
I tried using the Wigner matrices:

$$\sum_{m'=-2}^{2} {d^{(2)}}_{1m'} Y_{2; m'}={d^{(2)}}_{1 -2} Y_{2; -2} + {d^{(2)}}_{1 -1} Y_{2; -1} + ...= -\frac{1-\cos(\beta)}{2} \sin(\beta) \sqrt{\frac{15}{32 \pi}} \sin^2(\theta) e^{-i \phi} + ...$$

where $$\beta=\frac{\pi}{4}$$. But I don't know if this is ok since $$\beta$$ is an Euler angle while $$\theta$$ and $$\phi$$ are not. If this is not right, what should I do?
 
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  • #2
The angle ##\beta## will go away as it is replaced by the value of the rotation, leaving a function of ##(\theta,\phi)##, which is what you want.
 
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FAQ: Is the Rotation of Spherical Harmonics Using Wigner Matrices Correct?

What are spherical harmonics?

Spherical harmonics are mathematical functions that describe the angular portion of a set of solutions to Laplace's equation in spherical coordinates. They are often used in physical sciences and engineering to solve problems with spherical symmetry, such as gravitational and electromagnetic fields.

How do you rotate spherical harmonics?

Rotating spherical harmonics involves transforming them under a rotation of the coordinate system. This is typically done using Wigner D-matrices, which are representations of the rotation group SO(3). The rotated spherical harmonic can be expressed as a linear combination of the original harmonics with coefficients given by the Wigner D-matrix elements.

What are Wigner D-matrices?

Wigner D-matrices are a set of matrices that provide a representation of the rotation group, SO(3). They are used to describe how spherical harmonics transform under rotations. Each element of a Wigner D-matrix corresponds to a specific rotation and is used to calculate the rotated spherical harmonics.

Why is the rotation of spherical harmonics important?

The rotation of spherical harmonics is important in many fields such as quantum mechanics, geophysics, and computer graphics. In quantum mechanics, for example, it is used to describe the orientation of atomic orbitals. In geophysics, it helps in modeling the Earth's gravitational and magnetic fields. In computer graphics, it is used for efficient rendering of lighting and shading effects.

Can you provide an example of rotating a spherical harmonic?

Consider a spherical harmonic Yl,m(θ, φ). To rotate this harmonic by an angle α around the z-axis, the new harmonic can be expressed as a sum of the original harmonics multiplied by the corresponding Wigner D-matrix elements: Yl,m'(θ', φ') = Σ Dm',ml(α) Yl,m(θ, φ). Here, Dm',ml(α) are the elements of the Wigner D-matrix for the rotation.

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