Make AerSimulator own backend target object

[doichanj]

What is the expected behavior?

From Qiskit 1.0, quantum computer backend goes to BackendV2 (https://docs.quantum.ibm.com/api/qiskit/qiskit.providers.BackendV2) that has target object containing information of basis gates, coupling map, instruction properties (gate name, qubits, durations, gate error rates, etc). These properties are used for transpilation.
Currently Aer returns AerSimulator's target by using convert_to_target function (https://docs.quantum.ibm.com/api/qiskit/qiskit.providers.convert_to_target), but this target does not contain enough backend properties.
I think simulator backend should return these properties:

• coupling map with all-to-all qubits connectivity for given max number of qubits (MPS should return its connectivity ?)
• proper basis gates for each simulation method
• there is no error or error rates set from noise model (?)

One difficult thing to make target is most of users are initializing AerSimulator without parameters and we can not know number of qubits and simulation method at initialization.

Aer's backend is consist of 2 classes, AerBackend (https://github.com/Qiskit/qiskit-aer/blob/main/qiskit_aer/backends/aerbackend.py) is based on BackendV2 that should return proper target and properties objects and AerSinulator (https://github.com/Qiskit/qiskit-aer/blob/main/qiskit_aer/backends/aer_simulator.py) is simulation interface to users.

[ljcamargo]

Hi @doichanj so, is the goal here to create a totally new Target object just for Aer with this coupling maps, etc..? or just a new function such as "convert_to_enriched_target" to improve instatiation from BackendV1 with new new data. If a new Target class is needed I guess it should be sublclass of Target. Thanks

[doichanj]

I believe there is not large issue by using default target made from convert_to_target
So I think it is OK to study or evaluate if there is critical issues by using default target, or if there are good applications if there are customized targets specified for the simulator

[ljcamargo]

hi @doichanj I making progress in this, but I wonder if you have a test case for this because I'm not sure if the current tests or what I have tested so far cover everything. Thanks

[doichanj]

It is helpful for us if you can make good test cases