Source code for qolumbina.programs.bernstein_vazirani.bv

# This code is refactored by the Jupyter Notebook from
# https://github.com/Qiskit/textbook/blob/main/notebooks/ch-algorithms/bernstein-vazirani.ipynb
#
# The corresponding repository is
# https://github.com/Qiskit/textbook?tab=Apache-2.0-1-ov-file
#
# 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):
# - Refactored to unify the inherent class as QuantumCircuit:
# - Exposed unified program interfaces.
#
# This code is licensed under the Apache License, Version 2.0. You may
# obtain a copy of this license in the LICENSE.txt file in the root directory
# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.

from qiskit 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="Bernstein-Vazirani algorithm: Find a hidden binary string with a single oracle query.",
    class_name="BernsteinVazirani",
    source={
        "repo": "https://github.com/Qiskit/textbook?tab=Apache-2.0-1-ov-file",
        "file": "notebooks/ch-algorithms/bernstein-vazirani.ipynb",
        "sdk": "Qiskit",
        "available_doc": True
    },
    testability_refactoring=[
        "Structure reorganization"
    ],
)
def create_bv_circuit(
    secret: str, 
    insert_barriers: bool = False, 
    name: str | None = None
):
    return BernsteinVazirani(
        secret=secret, 
        insert_barriers=insert_barriers, 
        name=name
    )




class BernsteinVazirani(QuantumCircuit):
    r"""
    Bernstein-Vazirani algorithm circuit.

    Acts on :math:`n` input qubits and 1 auxiliary qubit
    """
    def __init__(self, secret: str, insert_barriers: bool = False, name: str | None = None):
        """
        Args:
            secret: The hidden binary string :math:`s`.
            insert_barriers: Whether to insert barriers in the circuit.
            name: Optional name for the circuit.
        
        Raises:
            ValueError: If ``secret`` is empty or contains characters other than ``'0'`` 
                and ``'1'``.
        """
        if not secret or any(c not in "01" for c in secret):
            raise ValueError("secret must be a non-empty binary string")

        self._secret = secret
        self._n = len(secret)
        self._insert_barriers = insert_barriers

        # ---------- registers ----------
        q_input = QuantumRegister(self._n, "q")
        q_aux = QuantumRegister(1, "aux")

        super().__init__(q_input, q_aux, name=name or "BV")
        self._build()

    # ---------- build ----------
    def _build(self) -> None:
        n = self._n

        # put auxiliary in state |->
        self.h(n)
        self.z(n)

        # Apply Hadamard gates before querying the oracle
        for i in range(n):
            self.h(i)
            
        # Apply barrier 
        if self._insert_barriers:
            self.barrier()

        # Apply the inner-product oracle
        s = self._secret[::-1] # reverse s to fit qiskit's qubit ordering
        for q in range(n):
            if s[q] == '0':
                self.id(q)
            else:
                self.cx(q, n)
                
        # Apply barrier 
        if self._insert_barriers:
            self.barrier()

        # Apply Hadamard gates after querying the oracle
        for i in range(n):
            self.h(i)