Source code for qolumbina.programs.state_preparation.ghz_state

# The original code is sourced from:
# https://github.com/munich-quantum-toolkit/bench/blob/main/src/mqt/bench/benchmarks/ghz.py
#
# This program is adapted for use as a benchmark in controlled software testing experiments.
# Modifications made to the original code include (for Apache License 2.0):
# - Modify the code in the class
# - Remove the measurements from the circuit
#
# 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

"""GHZ benchmark definition."""

from __future__ import annotations

from qiskit.circuit import QuantumCircuit, QuantumRegister

# ---------- benchmark registration ----------
from ..benchmark_registry import register_benchmark
from pathlib import Path
@register_benchmark(
    Path(__file__).stem,
    family=Path(__file__).resolve().parent.name,
    description="GHZ state preparation circuit",
    class_name="GHZState",
    source={
        "repo": "https://github.com/munich-quantum-toolkit/bench/tree/main",
        "file": "src/mqt/bench/benchmarks/ghz.py",
        "sdk": "Qiskit",
        "available_doc": False
    },
    testability_refactoring=[
        "Structure reorganization"
    ] 
)
def create_ghz_state(num_qubits: int):
    return GHZState(num_qubits=num_qubits)




class GHZState(QuantumCircuit):
    """
    Create a Greenberger-Horne-Zeilinger (GHZ) State:
    A GHZ state is an entangled quantum state of multiple qubits where all qubits are
    in a superposition of all being 0 or all being 1. 
    """
    def __init__(self, num_qubits: int, name: str | None = None) -> None:
        r"""
        Arguments:
            num_qubits: Number of qubits of the GHZ state.
            name: Name of the quantum circuit.
        """
        self._num_qubits = num_qubits

        super().__init__(num_qubits, name="ghz" or name)

        # Build the GHZ state circuit
        self._build()

    def _build(self) -> None:
        """Build the GHZ state circuit."""
        num_qubits = self._num_qubits

        q = QuantumRegister(num_qubits, "q")
        qc = QuantumCircuit(q, name="ghz")
        qc.h(q[-1])
        for i in range(1, num_qubits):
            qc.cx(q[num_qubits - i], q[num_qubits - i - 1])
        
        # qc.measure_all()

        self.compose(qc, qubits=self.qubits, inplace=True)