fix: Support single-register measurements in from_ir

[ashlhans]

Issue #, if available:
Currently, the statement b = measure q in an OpenQASM program results in the following error:

ValueError: Operator qubit count 1 must be equal to size of target qubit set QubitSet([Qubit(0), Qubit(1)])

This is because a measure instruction is always a 1 qubit instruction but right now, all the targets get added to the measure instruction even if there are more than 1 qubit measured.

To reproduce this issue:

bell_qasm = """
OPENQASM 3;

qubit[2] q;
bit[2] c;

h q[0];
cnot q[0], q[1];

c = measure q;
"""

from braket.circuits import Circuit
print(Circuit.from_ir(bell_qasm))

Description of changes:

• Add a loop to add a single measure instruction for each qubit target.
• Add a test to prevent this error in the future

Testing done:
tox and tox -e integ-tests

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (c57a9ba) to head (48bd56a).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #934   +/-   ##
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  Coverage   100.00%   100.00%           
=========================================
  Files          133       133           
  Lines         8905      8906    +1     
  Branches      2006      2007    +1     
=========================================
+ Hits          8905      8906    +1     

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[kshitijc]

Could we add tests to do a round trip transformation? Circuit -> OQ3 -> Circuit.from_ir and assert that the original and the parsed circuit are the same

[ashlhans]

I will add a round trip test.

This test_from_ir_with_single_measure test would not have the same OpenQASM output though because Circuit.from_ir would not output b = measure q since the BDK does not handle the measure assignment.

So instead it would output:

b[0] = measure q[0];
b[1] = measure q[1];

[speller26]

This is already covered by other test cases, right? Not that I'm complaining.

[ashlhans]

Yes, it is covered by other test cases