From 93deb42c2745b902b3190a5014f964e045638322 Mon Sep 17 00:00:00 2001
From: Noa Aarts <noa@voorwaarts.nl>
Date: Wed, 18 Mar 2026 10:22:44 +0100
Subject: [PATCH] pqc to qiskit conversion

---
 src/quantum_circuit/__init__.py       | 17 ++++++++
 src/quantum_circuit/qiskit_helpers.py | 58 ++++++++++++++++++++++++++-
 2 files changed, 73 insertions(+), 2 deletions(-)

diff --git a/src/quantum_circuit/__init__.py b/src/quantum_circuit/__init__.py
index 62f185f..f9b6c15 100644
--- a/src/quantum_circuit/__init__.py
+++ b/src/quantum_circuit/__init__.py
@@ -39,6 +39,17 @@ class QuantumType(enum.Enum):
             QuantumType.RZ,
         }
 
+    def is_parameterized(self):
+        return self in {
+            QuantumType.RX,
+            QuantumType.RXX,
+            QuantumType.RY,
+            QuantumType.RYY,
+            QuantumType.RZ,
+            QuantumType.RZZ,
+            QuantumType.CRX,
+        }
+
 
 @dataclass(frozen=True)
 class QuantumGate:
@@ -59,6 +70,9 @@ class ParametrizedQuantumCircuit:
     gates: list[list[QuantumGate]]
     """Gates in the quantum circuit, organised as a list of layers of gates."""
 
+    parameters: int
+    """How many parameters are used the circuit"""
+
     _expressivity: float | None = None
     """
     Expressivity of the circuit, following the definition from {THE PAPER}
@@ -90,6 +104,9 @@ class ParametrizedQuantumCircuit:
         """
         Add a layer to the end of the existing circuit in-place
         """
+        for gate in layer:
+            if gate.type.is_parameterized():
+                self.parameters += 1
         self.gates.append(layer)
 
     @property
diff --git a/src/quantum_circuit/qiskit_helpers.py b/src/quantum_circuit/qiskit_helpers.py
index 3daceff..a9476bc 100644
--- a/src/quantum_circuit/qiskit_helpers.py
+++ b/src/quantum_circuit/qiskit_helpers.py
@@ -1,11 +1,65 @@
 from typing import TYPE_CHECKING
 
 from qiskit import QuantumCircuit
+from qiskit.circuit.parameter import Parameter
 from qiskit.circuit.parametervector import ParameterVector
 
 if TYPE_CHECKING:
-    from quantum_circuit import ParametrizedQuantumCircuit
+    from quantum_circuit import (ParametrizedQuantumCircuit, QuantumGate,
+                                 QuantumType)
+
+
+def add_qubit_gate(circ: QuantumCircuit, gate: QuantumGate, theta: Parameter) -> int:
+    match gate.type:
+        case QuantumType.Identity:
+            return 0
+        case QuantumType.Hadamard:
+            circ.h(gate.qubits[0])
+            return 0
+        case QuantumType.X:
+            circ.x(gate.qubits[0])
+            return 0
+        case QuantumType.RX:
+            circ.rx(theta, gate.qubits[0])
+            return 1
+        case QuantumType.RXX:
+            circ.rxx(theta, gate.qubits[0], gate.qubits[1])  # ty:ignore[index-out-of-bounds]
+            return 1
+        case QuantumType.Y:
+            circ.y(gate.qubits[0])
+            return 0
+        case QuantumType.RY:
+            circ.ry(theta, gate.qubits[0])
+            return 1
+        case QuantumType.RYY:
+            circ.ryy(theta, gate.qubits[0], gate.qubits[1])  # ty:ignore[index-out-of-bounds]
+            return 1
+        case QuantumType.Z:
+            circ.z(gate.qubits[0])
+            return 0
+        case QuantumType.RZ:
+            circ.rz(theta, gate.qubits[0])
+            return 1
+        case QuantumType.RZZ:
+            circ.rzz(theta, gate.qubits[0], gate.qubits[1])  # ty:ignore[index-out-of-bounds]
+            return 1
+        case QuantumType.CRX:
+            circ.crx(theta, gate.qubits[0], gate.qubits[1])  # ty:ignore[index-out-of-bounds]
+            return 1
+        case QuantumType.CX:
+            circ.cx(gate.qubits[0], gate.qubits[1])  # ty:ignore[index-out-of-bounds]
+            return 0
+    raise NotImplementedError
 
 
 def build_qiskit_circ(pqc: "ParametrizedQuantumCircuit") -> tuple[QuantumCircuit, ParameterVector]:
-    raise NotImplementedError
+
+    circ = QuantumCircuit(pqc.qubits)
+    thetas = ParameterVector("thetas", circ.parameters)
+
+    current_theta_index = 0
+    for layer in pqc.gates:
+        for gate in layer:
+            current_theta_index += add_qubit_gate(circ, gate, thetas[current_theta_index])
+
+    return circ, thetas