Update simulator tutorials not to use deprecated APIs

[itoko]

• Update 1_aer_provider.ipynb.ipynb to avoid deprecation warning.
• Update 5_noise_transformation.ipynb not to use the deprecated arguments in approximate_quantum_error function.

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[HuangJunye]

Line #14.    print("Circuit unitary:\n", np.asarray(unitary).round(5))

What is the reason for this change? It seems to me that the outcome is the same.

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[itoko]

This change is because Aer's save_unitary changed its return type from numpy.array to quantum_info.Operator. Without this change, this line will raise DeprecationWarning like

DeprecationWarning: The return type of saved unitaries has been changed from a `numpy.ndarray` to a `qiskit.quantum_info.Operator` as of qiskit-aer 0.10. Accessing numpy array attributes is deprecated and will result in an error in a future release. To continue using saved result objects as arrays you can explicitly cast them using  `np.asarray(object)`.
  print("Circuit unitary:\n", unitary.round(5))

[HuangJunye]

Line #4.    results = approximate_quantum_error(Kraus([K0, K1]), operator_string="reset")

I am not familiar with this function in Aer. Can you provide a bit of context for this change?

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[itoko]

This change is because approximate_quantum_error changed the acceptable type of the first argument to be QuantumError or QuantumChannel. Without this change, this line will raise

DeprecationWarning: Support of types other than QuantumError or QuantumChannel for error to be approximated has been deprecated as of qiskit-aer 0.10.0 and will be removed no earlier than 3 months from that release date.
  results = approximate_quantum_error([K0, K1], operator_string="reset")

[HuangJunye]

The changes look reasonable however I don't have the full context on why the changes are necessary. Can you please provide some context in the PR descriptions and link to related PRs so that people (me and others, and in the future) can understand better?

[itoko]

Thanks, @HuangJunye. Excuse me for not providing a context of this PR. All changes in this PR are updates for avoiding the use of deprecated APIs in Aer so that these tutorials continue to work after removing the deprecated functions. (Actually, some deprecated functions are about to remove in Aer: Qiskit/qiskit-aer#1624)

[HuangJunye]

@itoko thanks for providing the context; they are really helpful for understanding the change.