About writing a unitary matrix in another way

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Discussion Overview

The discussion revolves around the representation of unitary matrices, specifically how a unitary matrix can be expressed in a certain form. Participants explore the conditions that must be satisfied for a matrix to be unitary, including determinant constraints and relationships between its elements.

Discussion Character

  • Technical explanation, Mathematical reasoning, Debate/contested

Main Points Raised

  • One participant asserts that a matrix of a specific form is unitary if it satisfies the condition \(AA^* = I\) and has a determinant of 1.
  • Another participant proposes starting with the most general form of a 2x2 matrix and deriving the necessary conditions for unitarity, suggesting that certain relationships among the matrix elements must hold.
  • A participant expresses difficulty in deriving the relationships due to the complexity of the resulting equations involving multiple real numbers.
  • Another participant suggests using the inverse of the matrix and its Hermitian to determine the necessary relationships among the matrix elements, referencing the relationship \(A^\dagger = A^{-1}\).

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the best approach to demonstrate the representation of a unitary matrix, with differing opinions on methods and the complexity of the equations involved.

Contextual Notes

Some participants note the need for specific conditions, such as the determinant being equal to 1, but the discussion does not resolve the implications of these conditions or the completeness of the proposed methods.

aalma
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It is easy to see that a matrix of the given form is actually an unitary matrix i,e, satisfying AA^*=I with determinant 1. But, how to see that an unitary matrix can be represented in the given way?
20230322_224305.jpg
 
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Take the most general matrix,
$$
A =
\begin{bmatrix}
a + bi & c + di \\
e+ fi & g+hi
\end{bmatrix}
$$
and show that imposing ##AA^\dagger = I## requires ##e = -c##, ##f=d##, and so on.
 
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Yes, thanks. Tried to do this however got somehow long equations with these eight real numbers. guessing how it should be solved!
I also wrote the condition that the det of this matrix=1.
 
Can't you just find the inverse of the matrix using the standard formula, and then you do the hermitian of the matrix and thus figure out what the relationsships of a, b, c, ... must be?

##A^\dagger = A^{-1}##
 
Last edited:
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