B2: Phase Shift Oracle

Problem Statement

You are given integers $n,\ L$, and a real number $\theta$.
Implement the oracle $O$ on a quantum circuit $\mathrm{qc}$ with $n$ qubits acting on computational basis states as

for any integer $y$ such that $0 \leq y < 2^n$.

Constraints

• $1 \leq n \leq 10$
• $0 \leq L < 2^n$
• $0 \leq \theta < 2\pi$
• Integers are encoded by little-endian notation, i.e., $\ket{100} = 1 \neq \ket{001}$.
• Changes in the global phase are ignored.
  
• The submitted code must follow the specified format:

from qiskit import QuantumCircuit
 
 
def solve(n: int, L: int, theta: float) -> QuantumCircuit:
    qc = QuantumCircuit(n)
    # Write your code here:
 
    return qc

Sample Input

• $n = 2,\ L = 1,\ \theta = \pi/2$
  The implemented quantum circuit $\mathrm{qc}$ should perform the following transformation.