Qiskit / qiskit / 27709717261

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Commit Message

Var-based measurement experiments (#16273)

* Initial exploratory support for measuring to Var-indexed clbit and usage of Uint var in for loops

* Linting, test fix

* Remove the simulator - it cannot be used to test circuits with `store` instructions

* Linting

* Overhaul

* Small fixes

* A quick solution to the qpy problem

* DAG comparision fix

* Remove irrelevant test; the qasm3 and the qpy test are the ones needed

* Writing/Reading the LoopParam var by explicitly looking inside the nested circuit

* Use `input` var as for-loop `Var` parameters

Semantically, the loop parameter of a for loop isn't a local-scope
variable of the block body, because otherwise there'd be no way to refer
to how the value is "set" from one iteration of the loop to the other.
Instead, it's owned by the implicit "header" of the loop that deals with
assigning the iteration, and then input into the loop body.

As well as the semantic benefit, relaxing the circuit data model to
permit this makes it cleaner to re-infer from a `ForLoopOp` body what
the loop parameter is in other cases, like QPY.

* Use `input`-Var inference in QPY

This reduces the additional data and semantics that need to be
transmitted through QPY for `ForLoopOp`; the circuit data model only
permits an `input` var in a body in the case of an `expr.Var` parameter,
and the length must be exactly one in that case.

* Small fixes

* Linting

* Return the reader code that was dropped in the merge

* Release note and cleanup of leftovers I thought were already removed

* Fixes according to PR review

* Test fixes

---------

Co-authored-by: Jake Lishman <jake.lishman@ibm.com>

Coverage Stats

74 of 95 new or added lines in 14 files covered. (77.89%)

21 existing lines in 6 files now uncovered.

111560 of 127443 relevant lines covered (87.54%)

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