Source code for qolumbina.programs.hamiltonian.diagonal_hamiltonian

# This code is developed through cross-language conversion from 
# https://github.com/MgcosA/Code_of_Testing_Oracle_Quantum_Program_Article/blob/master/qolumbina/programs/HamiltonX.qs
# 
# In detail, the raw program is written in Q#, and we rewrite it in Qiskit.

from qiskit import QuantumCircuit

# ---------- benchmark registration ----------
from ..benchmark_registry import register_benchmark
from pathlib import Path
@register_benchmark(
    Path(__file__).stem,
    family=Path(__file__).resolve().parent.name,
    description="Hamiltonian evolution for diagonal Z Hamiltonian",
    class_name="DiagonalZHamiltonian",
    source={
        "repo": "https://github.com/MgcosA/Code_of_Testing_Oracle_Quantum_Program_Article/blob/master/",
        "file": "qolumbina/programs/HamiltonX.qs",
        "sdk": "Q#",
        "available_doc": True        
    },
    testability_refactoring=[
        "Cross-language translation", 
        "Structure reorganization",
        "Input validation"  # Ensure $n$ and $t$ are positive
    ] 
)
def create_diagonal_z_hamiltonian(input_qubits, t):
    return DiagonalZHamiltonian(input_qubits=input_qubits, t=t)




class DiagonalZHamiltonian(QuantumCircuit):
    r"""
    Implements the Hamiltonian evolution exp(-i * H * t) using only single-qubit Rz gates.
    """
    def __init__(self, input_qubits: int, t: float, name: str | None = None):
        r"""
        Args:
            input_qubits: Number of qubits in the system (:math:`n`).
            t: Evolution time :math:`t` (:math:`t > 0`).
            name: Optional name for the circuit.
        
        Raises:
            ValueError: If ``t`` is negative.
        """
        if t < 0:
            raise ValueError("t should be non-negative")

        super().__init__(input_qubits, name=name or "DiagonalZHamiltonian")
        self._time = t
        self._input_qubits = input_qubits
        self._build()

    # ---------- build ----------    
    def _build(self) -> None:
        qs = self.qubits
        n = len(qs)

        # Apply Rz rotation for each qubit according to 2^i scaling
        for i in range(n):
            angle = self._time * (2 ** i)  # t * IntAsDouble(2 ^ i)
            self.rz(angle, qs[i])