MixedOp implementation #3
Conversation
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I will review this in ~2 weeks 👍 |
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| @@ -110,7 +114,7 @@ class QubitConverter: | |||
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| def __init__( | |||
| self, | |||
| mapper: QubitMapper, | |||
| mappers: Sequence[QubitMapper], | |||
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A scalable approach for the future will need to use a Mapping instead of sequence here which then maps from operator type to mapper.
Alternatively, we could also envision inferring the compatible operator type from a mapper instance and then use a Collection (i.e. set of mappers).
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And arguable we should still support specifying only a single mapper (i.e. with | QubitMapper). I think the code below does this, but the type hint does not reflect this
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| # convert all fermionics and store in list | ||
| qubit_f_ops = [] | ||
| max_f_reg_length = 0 |
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We should actually check, that all result in identical length operators. Otherwise something is likely wrong
| qubit_ops = [] | ||
| for c in mix_coefficients: | ||
| if len(c[0]) > 1: | ||
| qubit_ops.append(qubit_f_ops[c[0][0][1]] ^ qubit_s_ops[c[0][1][1]] * c[1]) |
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Accessing of the coefficients is a bit cryptic here. Probably more comments on that down below in the MixedOp
| # convert all spins and store in list | ||
| qubit_s_ops = [] | ||
| max_s_reg_length = 0 | ||
| for s_op in operators[SpinOp]: | ||
| q_op = apply_map_sym(s_op, spin_mapper) | ||
| max_s_reg_length = q_op.num_qubits if q_op.num_qubits > max_s_reg_length else max_s_reg_length | ||
| qubit_s_ops.append(q_op) |
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I know that this prototype is currently hardcoding fermionic and spin ops, but we should try to design this block of code as a type-independent standalone piece of code.
This could then also be combined with the identity construction below.
| else: | ||
| return self._mappers.map(second_q_op) | ||
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| def _map_multiple(self, second_q_op: MixedOp) -> PauliSumOp: |
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Can we generalize this implementation to not be map specific but only deal with handling a MixedOp, such that it can work with an arbitrary internal method such as _map, _two_qubit_reduce, etc. ?
| from .mixed_op import MixedOp | ||
| return MixedOp(([self, other], 1)) |
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I think it should be possible to leave the base operators unchanged, by handling this scenario in the MixedOp.__rmatmul__ case 🤔
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I'm not sure how we could do this for the case FermionicOp @ SpinOp, because there isn't any MixedOp involved yet, so MixedOp.__rmatmul__ would not be called, right?
| if type(op) in self.ops: | ||
| self.ops[type(op)].append(op) | ||
| else: | ||
| self.ops[type(op)] = [op] |
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You could simplify this by using a defaultdict(list) for self.ops
| ) | ||
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| def __len__(self): | ||
| return len(self.ops[FermionicOp]) + len(self.ops[SpinOp]) |
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| return len(self.ops[FermionicOp]) + len(self.ops[SpinOp]) | |
| return sum(len(val) for val in self.ops.values()) |
…o mixed-op Pull changes from origin
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Hello! I will be branching this repo since the lattice gauge theory needs MixedOps. That would potentially make it easier for Max to review the code. This way I can also give feedback in case something breaks. |
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Closing this in favor of qiskit-community#1188 |
Summary
This is a PR to expose my PoC for the
MixedOpimplementation and corresponding extension of theQubitConverterclass.Apart from the corresponding classes, there are 2 PoC files (not in the best location) to show the functionality that has been implemented. I recommend taking a look at this one.
Details and comments
Implemented:
MixedOpclass that supports:- Multiplication with scalar
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MixedOpadditionrepr()andlen()methodsFermionicOpto returnMixedOpFermionicOp @ SpinOp, any other order or classes will not work!QubitConverterto supportMixedOpMissing:
MixedOp+MixedOprepr(), etcQubitConverter, including proper logic to deal with symmetry reductions in theMixedOpcase.