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I have these two 4x4 matrix

Subscript[S, 1] = KroneckerProduct[PauliMatrix[1], IdentityMatrix[2]]
Subscript[S, 2] = KroneckerProduct[IdentityMatrix[2], PauliMatrix[2]]

Which are written in the Canonical basis ({{{1}, {0}, {0}, {0}};{{{0}, {1}, {0}, {0}}; {{{0}, {0}, {1}, {0}}; {{{0}, {0}, {0}, {1}})

I would like to write down these two matrices in the following basis:

G := {{0}, {0}, {0}, {1}}

S := (1/Sqrt[2]) {{0}, {1}, {1}, {0}}

A := (1/Sqrt[2]) {{0}, {1}, {-1}, {0}}

EE := {{1}, {0}, {0}, {0}}

Is there any way to do it in Mathematica?

Thanks in advance

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1 Answer 1

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Should be

Subscript[S, 1] = KroneckerProduct[PauliMatrix[1], IdentityMatrix[2]]
Subscript[S, 2] = KroneckerProduct[IdentityMatrix[2], PauliMatrix[2]]
basis = {{0, 0, 0, 1}, (1/Sqrt[2]) {0, 1, 1, 0}, (1/Sqrt[2]) {0, 1, -1, 0}, {1, 0, 0, 0}};
Inverse[basis].Subscript[S, 1].Transpose[basis]
Inverse[basis].Subscript[S, 2].Transpose[basis]

{{0, 1/Sqrt[2], 1/Sqrt[2], 0}, {1/Sqrt[2], 0, 0, 1/Sqrt[2]}, {1/Sqrt[ 2], 0, 0, -(1/Sqrt[2])}, {0, 1/Sqrt[2], -(1/Sqrt[2]), 0}}

{{0, I/Sqrt[2], -(I/Sqrt[2]), 0}, {-(I/Sqrt[2]), 0, 0, I/Sqrt[2]}, {I/ Sqrt[2], 0, 0, I/Sqrt[2]}, {0, -(I/Sqrt[2]), -(I/Sqrt[2]), 0}}

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  • $\begingroup$ I understood what you have done but when I reply it I do not get a matrix as the result. Instead, I get only the full expression of the products. $\endgroup$
    – Soares
    Jul 21, 2021 at 23:31
  • $\begingroup$ Of course, you have to define Subscript[S, 1] and Subscript[S, 2], first. $\endgroup$ Jul 22, 2021 at 12:29

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