Changes TODO in the code

Remove get_register (PARTIALLY DONE)

• Potential changes:
  • Generate new instance of ClassicalRegister in the _process_QuantumMeasurementAssignment
  • Perform circuit.add_register()
  • Perform cl_identifier.set_register()
• Will make the syntax for measurement operation easier and constant with the other things that use context.lookup() instead.
• Problems:
  • Need some way to not process IndexIdentifier, and perform indexing/selection/slicing on the ClassicalRegister instead.
  • Conflict with language specification as it gives a way to add register to types other than BitArrayType as well.

BranchingStatement

• Determine if the condition is a measurement result that is stored in a ClassicalRegister object using:
  1 2	if <ClassicalType>.register is None: ...

• If register is None, then go for _process_Statement
• Else use c_if with the quantum gates inside the if-else block.

ForInLoop

• Determine is loop is constant time unrollable or not.
• Have to look-ahead in the AST for evaluating unrollability.

• Probably a recursive backtracking style look-ahead would be easier to implement as per the current translator code.

• Unrollable:
  • Only consisting of quantum gates.
  • Just unroll the loop into a serial set of quantum gates.
• Non-unrollable:
  • Consisting of quantum gates, measurements, classical operations, classical feedback, quantum-classical loop dependencies etc.
  • Generate a separate quantum circuit for the loop block and then use qc.compose() to join initial circuit with circuit for each iter.
  • Problem: The number of circuits will grow exponentially for nested loops.

All attrs

• Accept a list of QuantumCircuit objects.
  • First instance: main circuit.
  • Subsequenct instances: circuit for each iteration.

translate()

• Return a list of QuantumCircuit objects.