Add IQPE benchmark

pyproject.toml

@@ -21,7 +21,7 @@ dynamic = ["version"]
 
 dependencies = [
     # Qiskit 1.3.2 contains some fixes for exporting OpenQASM 3 files
-    "qiskit[qasm3-import]>=1.3.2",
+    "qiskit[qasm3-import]>=2.0.0",
     "networkx>=2.8.8",
     "numpy>=1.22",
     "numpy>=1.24; python_version >= '3.11'",

src/mqt/bench/benchmarks/iqpe_exact.py

@@ -0,0 +1,89 @@
+# Copyright (c) 2023 - 2026 Chair for Design Automation, TUM
+# Copyright (c) 2025 - 2026 Munich Quantum Software Company GmbH
+# All rights reserved.
+#
+# SPDX-License-Identifier: MIT
+#
+# Licensed under the MIT License
+
+"""Iterative Quantum Phase Estimation (IQPE)."""
+
+from __future__ import annotations
+
+import random
+from fractions import Fraction
+
+import numpy as np
+from qiskit.circuit import ClassicalRegister, QuantumCircuit, QuantumRegister
+
+from ._registry import register_benchmark
+
+
+@register_benchmark("iqpe_exact", description="Iterative Quantum Phase Estimation (IQPE)")
+def create_circuit(num_qubits: int) -> QuantumCircuit:
+    """Returns a dynamic quantum circuit implementing the Iterative Quantum Phase Estimation algorithm.
+
+    Arguments:
+        num_qubits: total number of qubits.
+
+    Returns:
+        QuantumCircuit: a dynamic quantum circuit implementing the Iterative Quantum Phase Estimation algorithm for a phase which can be exactly estimated
+
+    """
+    # We just use 2 quantum registers: q[1] is the main register where
+    # the eigenstate will be encoded, q[0] is the ancillary qubit where the phase
+    # will be encoded. Only the ancillary qubit is measured, and the result will
+    # be stored in "c", the classical register.
+    if num_qubits < 2:
+        msg = "num_qubits must be >= 2 (1 ancilla + at least 1 phase bit)"
+        raise ValueError(msg)
+    num_bits = num_qubits - 1  # because of ancilla qubit
+    q = QuantumRegister(num_qubits, "q")
+    c = ClassicalRegister(num_bits, "c")
+    qc = QuantumCircuit(q, c, name="iqpe_exact")
+
+    # Generate a random n-bit integer as a target phase "theta". The phase can be exactly
+    # estimated
+    rng = random.Random(10)
+    theta = 0
+    while theta == 0:
+        theta = rng.getrandbits(num_bits)
+    lam = Fraction(0, 1)
+    for i in range(num_bits):
+        if theta & (1 << (num_bits - i - 1)):
+            lam += Fraction(1, (1 << i))
+
+    # We apply an X gate to the q[1] qubit, to prepare the target qubit in the
+    # |1> state
+    qc.x(q[1])
+
+    for k in range(num_bits):
+        index = num_bits - 1 - k
+        # We reset the ancillary qubit in order to reuse in each iteration
+        qc.measure(q[0], c[0])
+        with qc.if_test((c[0], 1)):
+            qc.x(q[0])
+        qc.h(q[0])
+
+        # Controlled unitary. The angle is normalized from
+        # [0, 2] to [-1, 1], which minimize the errors because uses shortest rotations
+        angle = float((lam * (1 << index)) % 2)
+        if angle > 1:
+            angle -= 2
+
+        # We use pi convention for simplicity
+        qc.cp(angle * np.pi, q[0], q[1])
+
+        # We apply phase corrections based on previous measurements.
+        for i in range(k):
+            m_index = num_bits - 1 - i
+            true_angle = -1.0 / (1 << (k - i))
+
+            with qc.if_test((c[m_index], 1)):
+                qc.p(true_angle * np.pi, q[0])
+
+        qc.h(q[0])
+        # We measure and store the result for future corrections
+        qc.measure(q[0], c[index])
+
+    return qc

tests/test_bench.py

@@ -145,6 +145,34 @@ def test_adder_circuits(benchmark_name: str, input_value: int, kind: str) -> Non
     assert qc.num_qubits == input_value
 
 
+def test_iqpe_exact_structure() -> None:
+    """Test that the Iterative Quantum Phase Estimation code circuit has the expected structure.
+
+    Verifies (for a 5-qubit input):
+        - Quantum registers: 4 target qubits and 1 ancillary qubit
+        - Classical register: num_qubits - 1 (4 bits)
+        - 8 measurements (4 resets + 4 final measurements)
+        - 10 conditional operations (4 reset conditionals + 6 correction conditionals)
+    """
+    qc = create_circuit("iqpe_exact", 5)
+
+    assert qc.num_qubits == 5
+    assert qc.num_clbits == 4
+
+    ops = qc.count_ops()
+    ops = dict(ops)  # type: dict[str, int]
+    assert ops.get("measure") == 8
+
+    if_else_count = sum(1 for inst in qc.data if inst.operation.name == "if_else")
+    assert if_else_count == 10, f"Expected 10 conditional operations, found {if_else_count}"
+
+
+def test_iqpe_exact_invalid_qubit_number() -> None:
+    """Test that the Iterative Quantum Phase Estimation code circuit raises an error for invalid qubit numbers."""
+    with pytest.raises(ValueError, match=r"num_qubits must be >= 2"):
+        create_circuit("iqpe_exact", 1)
+
+
 @pytest.mark.parametrize(
     ("benchmark_name", "input_value", "kind", "msg"),
     [