Unify notation in the quantum_info documentation

[renatomello]

This PR unifies notation between the quantum info module and its upcoming paper

Checklist:

• Reviewers confirm new code works as expected.
• Tests are passing.
• Coverage does not decrease.
• Documentation is updated.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.38%. Comparing base (dfd80ea) to head (66d92b1).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1511   +/-   ##
=======================================
  Coverage   99.38%   99.38%           
=======================================
  Files          78       78           
  Lines       13057    13058    +1     
=======================================
+ Hits        12977    12978    +1     
  Misses         80       80           

Flag	Coverage Δ
unittests	99.38% <100.00%> (+<0.01%)	⬆️

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