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Is every unitary matrix hermitian

Updated: 4/28/2022
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14y ago

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Absolutely not.

They are rather quite different: hermitian matrices usually change the norm of vector while unitary ones do not (you can convince yourself by taking the spectral decomposition: eigenvalues of unitary operators are phase factors while an hermitian matrix has real numbers as eigenvalues so they modify the norm of vectors). So unitary matrices are good "maps" whiule hermitian ones are not.

If you think about it a little bit you will be able to demonstrate the following:

for every Hilbert space except C^2 a unitary matrix cannot be hermitian and vice versa.

For the particular case H=C^2 this is not true (e.g. Pauli matrices are hermitian and unitary).

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Q: Is every unitary matrix hermitian
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