Statefunction ket-bra composition

[hadizadeh-ali]

What is the expected behavior?

Code:

from qiskit.opflow import Zero
Zero @ ~Zero

Suggested output: e.g., a MatrixOp equivalent to |0⟩⟨0|.

Output now:

File "D:\Programs\Anaconda\Anaconda3-2019.10\install\envs\envi\lib\site-packages\qiskit\opflow\mixins\star_algebra.py", line 107, in __matmul__
    return self.compose(other)
  File "D:\Programs\Anaconda\Anaconda3-2019.10\install\envs\envi\lib\site-packages\qiskit\opflow\state_fns\state_fn.py", line 306, in compose
    raise ValueError(
ValueError: Composition with a Statefunction in the first operand is not defined.

>>> qiskit.__qiskit_version__
{'qiskit-terra': '0.23.2', 'qiskit-aer': '0.12.0', 'qiskit-ignis': '0.7.1', 'qiskit-ibmq-provider': '0.20.2', 'qiskit': '0.42.0', 'qiskit-nature': None, 'qiskit-finance': None, 'qiskit-optimization': None, 'qiskit-machine-learning': None}

[woodsp-ibm]

#9176 is about to deprecate opflow for this upcoming next release, ahead of its removal, in the future, following that. During this period, until removal, it will be continue to be supported (critical bug fixes) but no new features/enhancements would be included. #9484 will add a migration guide to using comparable function from quantum_info module where it exists.