[fix] Automated decomposition of Rabi into an Amplitude and phase term

[yhteoh]

• Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  Fix

• What is the current behavior? (You can also link to an open issue here)
  non-positive Rabi frequencies unsupported (Unsupported negative rabi frequency #40)

• What is the new behavior (if this is a feature change)?
  Canonicalization applies the following to decompose the Rabi frequency into a positive amplitude and a phase term:

$$\begin{gather} \Omega = A+iB = |\Omega| e^{i \phi} \\\ \phi = \arctan \left( \frac{B}{A} \right) \end{gather}$$

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
  No

• Other information: