Add multi-control functionality #1380
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| Original file line number | Diff line number | Diff line change |
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@@ -307,6 +307,127 @@ void FunctionalityConstruction::addCcx(ZXDiagram& diag, const Qubit ctrl0, | |
| addCnot(diag, ctrl0, ctrl1, qubits); | ||
| } | ||
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| void FunctionalityConstruction::addCcz(ZXDiagram& diag, const Qubit ctrl0, | ||
| const Qubit ctrl1, const Qubit target, | ||
| std::vector<Vertex>& qubits) { | ||
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| addCnot(diag, ctrl1, target, qubits); | ||
| addZSpider(diag, target, qubits, PiExpression(PiRational(-1, 4))); | ||
| addCnot(diag, ctrl0, target, qubits); | ||
| addZSpider(diag, target, qubits, PiExpression(PiRational(1, 4))); | ||
| addCnot(diag, ctrl1, target, qubits); | ||
| addZSpider(diag, ctrl1, qubits, PiExpression(PiRational(1, 4))); | ||
| addZSpider(diag, target, qubits, PiExpression(PiRational(-1, 4))); | ||
| addCnot(diag, ctrl0, target, qubits); | ||
| addZSpider(diag, target, qubits, PiExpression(PiRational(1, 4))); | ||
| addCnot(diag, ctrl0, ctrl1, qubits); | ||
| addZSpider(diag, ctrl0, qubits, PiExpression(PiRational(1, 4))); | ||
| addZSpider(diag, ctrl1, qubits, PiExpression(PiRational(-1, 4))); | ||
| addZSpider(diag, target, qubits, PiExpression(PiRational(0, 1)), | ||
| EdgeType::Hadamard); | ||
| addCnot(diag, ctrl0, ctrl1, qubits); | ||
| addZSpider(diag, target, qubits, PiExpression(), EdgeType::Hadamard); | ||
| } | ||
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| void FunctionalityConstruction::addCrz(ZXDiagram& diag, | ||
| const PiExpression& phase, | ||
| const Qubit q0, const Qubit q1, | ||
| std::vector<Vertex>& qubits) { | ||
| // CRZ decomposition uses reversed CNOT direction | ||
| addCnot(diag, q1, q0, qubits); | ||
| addZSpider(diag, q0, qubits, -phase / 2); | ||
| addZSpider(diag, q1, qubits, phase / 2); | ||
| addCnot(diag, q1, q0, qubits); | ||
| } | ||
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| void FunctionalityConstruction::addMcrz(ZXDiagram& diag, | ||
| const PiExpression& phase, | ||
| std::vector<Qubit> controls, | ||
| const Qubit target, | ||
| std::vector<Vertex>& qubits) { | ||
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| const Qubit nextControl = controls.back(); | ||
| controls.pop_back(); | ||
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| addCrz(diag, phase / 2, nextControl, target, qubits); | ||
| addMcx(diag, controls, target, qubits); | ||
| addCrz(diag, -phase / 2, nextControl, target, qubits); | ||
| addMcx(diag, controls, target, qubits); | ||
| } | ||
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| void FunctionalityConstruction::addMcx(ZXDiagram& diag, | ||
| std::vector<Qubit> controls, | ||
| const Qubit target, | ||
| std::vector<Vertex>& qubits) { | ||
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| switch (controls.size()) { | ||
| case 0: | ||
| addXSpider(diag, target, qubits, PiExpression(PiRational(1, 1))); | ||
| return; | ||
| case 1: | ||
| addCnot(diag, controls.front(), target, qubits); | ||
| return; | ||
| case 2: | ||
| addCcx(diag, controls.front(), controls.back(), target, qubits); | ||
| return; | ||
| default: | ||
| const auto half = static_cast<std::ptrdiff_t>((controls.size() + 1) / 2); | ||
| const std::vector<Qubit> first(controls.begin(), controls.begin() + half); | ||
| std::vector<Qubit> second(controls.begin() + half, controls.end()); | ||
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| if (qubits.size() > controls.size() + 1) { | ||
| controls.push_back(target); | ||
| std::optional<Qubit> anc{}; | ||
| for (std::size_t q = 0; q < qubits.size(); ++q) { | ||
| const auto qb = static_cast<Qubit>(q); | ||
| if (std::ranges::find(controls, qb) == controls.end()) { | ||
| anc = qb; | ||
| break; | ||
| } | ||
| } | ||
| if (!anc.has_value()) { | ||
| throw ZXException("No ancilla qubit available for MCX decomposition"); | ||
| } | ||
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Member
There was a problem hiding this comment. This is unreachable code, right? There are more than I also think that you could be using https://en.cppreference.com/w/cpp/algorithm/set_difference.html here. |
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| controls.pop_back(); | ||
| second.push_back(*anc); | ||
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| addMcx(diag, first, *anc, qubits); | ||
| addMcx(diag, second, target, qubits); | ||
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| addMcx(diag, first, *anc, qubits); | ||
| addMcx(diag, second, target, qubits); | ||
| } else { | ||
| addRx(diag, PiExpression(PiRational(1, 4)), target, qubits); | ||
| addMcz(diag, second, target, qubits); | ||
| addRx(diag, PiExpression(-PiRational(1, 4)), target, qubits); | ||
| addMcx(diag, first, target, qubits); | ||
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| addRx(diag, PiExpression(PiRational(1, 4)), target, qubits); | ||
| addMcz(diag, second, target, qubits); | ||
| addRx(diag, PiExpression(-PiRational(1, 4)), target, qubits); | ||
| addMcx(diag, first, target, qubits); | ||
| const Qubit lastControl = controls.back(); | ||
| controls.pop_back(); | ||
| addMcrz(diag, PiExpression(PiRational(1, 2)), controls, lastControl, | ||
| qubits); | ||
| } | ||
| } | ||
| } | ||
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| void FunctionalityConstruction::addMcz(ZXDiagram& diag, | ||
| std::vector<Qubit> controls, | ||
| const Qubit target, | ||
| std::vector<Vertex>& qubits) { | ||
| const Qubit nextControl = controls.back(); | ||
| controls.pop_back(); | ||
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| addCrz(diag, PiExpression(PiRational(1, 2)), nextControl, target, qubits); | ||
| addMcx(diag, controls, target, qubits); | ||
| addCrz(diag, PiExpression(-PiRational(1, 2)), nextControl, target, qubits); | ||
| addMcx(diag, controls, target, qubits); | ||
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Member
There was a problem hiding this comment. Wouldn't it be easier to either:
Does one of these yield a shorter decomposition? |
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| } | ||
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| FunctionalityConstruction::op_it | ||
| FunctionalityConstruction::parseOp(ZXDiagram& diag, op_it it, op_it end, | ||
| std::vector<Vertex>& qubits, | ||
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@@ -538,6 +659,9 @@ FunctionalityConstruction::parseOp(ZXDiagram& diag, op_it it, op_it end, | |
| qubits[static_cast<std::size_t>(target)], | ||
| EdgeType::Hadamard); | ||
| break; | ||
| case qc::OpType::RZ: | ||
| addCrz(diag, parseParam(op.get(), 0), ctrl, target, qubits); | ||
| break; | ||
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| case qc::OpType::I: | ||
| break; | ||
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@@ -578,15 +702,39 @@ FunctionalityConstruction::parseOp(ZXDiagram& diag, op_it it, op_it end, | |
| ctrl1 = static_cast<Qubit>(p.at(ctrl.qubit)); | ||
| } | ||
| } | ||
| std::vector<Qubit> controls; | ||
| for (const auto& ctrl : op->getControls()) { | ||
| controls.push_back(static_cast<Qubit>(p.at(ctrl.qubit))); | ||
| } | ||
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Member
There was a problem hiding this comment. This can just be inlined as |
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| switch (op->getType()) { | ||
| case qc::OpType::X: | ||
| addCcx(diag, ctrl0, ctrl1, target, qubits); | ||
| break; | ||
| case qc::OpType::Z: | ||
| addCcz(diag, ctrl0, ctrl1, target, qubits); | ||
| break; | ||
| case qc::OpType::RZ: | ||
| addMcrz(diag, parseParam(op.get(), 0), controls, target, qubits); | ||
| break; | ||
| default: | ||
| throw ZXException("Unsupported Multi-control operation: " + | ||
| qc::toString(op->getType())); | ||
| } | ||
| } else if (op->getNtargets() == 1) { | ||
| const auto target = static_cast<Qubit>(p.at(op->getTargets().front())); | ||
| std::vector<Qubit> controls; | ||
| for (const auto& ctrl : op->getControls()) { | ||
| controls.push_back(static_cast<Qubit>(p.at(ctrl.qubit))); | ||
| } | ||
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There was a problem hiding this comment. Always good to use |
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| switch (op->getType()) { | ||
| case qc::OpType::X: | ||
| addMcx(diag, controls, target, qubits); | ||
| break; | ||
| case qc::OpType::Z: | ||
| addMcz(diag, controls, target, qubits); | ||
| break; | ||
| case qc::OpType::RZ: | ||
| addMcrz(diag, parseParam(op.get(), 0), controls, target, qubits); | ||
| break; | ||
| default: | ||
| throw ZXException("Unsupported Multi-control operation: " + | ||
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@@ -701,15 +849,16 @@ bool FunctionalityConstruction::transformableToZX(const qc::Operation* op) { | |
| case qc::OpType::S: | ||
| case qc::OpType::Tdg: | ||
| case qc::OpType::Sdg: | ||
| case qc::OpType::RZ: | ||
| return true; | ||
| default: | ||
| return false; | ||
| } | ||
| } else if (op->getNtargets() == 1) { | ||
| switch (op->getType()) { | ||
| case qc::OpType::X: | ||
| case qc::OpType::Z: | ||
| case qc::OpType::RZ: | ||
| return true; | ||
| default: | ||
| return false; | ||
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These commute, so it does not really matter too much, but for consistency with the
mcrzpatter, I'd prefer this order.