| """
|
| Unit tests for dense_evolution/qft.py -- cross-checked against the
|
| brute-force analytic DFT matrix, not just against its own derivation.
|
| """
|
| import numpy as np
|
| import pytest
|
|
|
| from dense_evolution import DenseSVSimulator
|
| from dense_evolution.qft import qft
|
|
|
|
|
| def _dft_matrix(dim):
|
| """M[j, k] = exp(2*pi*i*j*k/dim) / sqrt(dim), so QFT|j> = sum_k M[j,k]|k>."""
|
| j_idx, k_idx = np.meshgrid(np.arange(dim), np.arange(dim), indexing='ij')
|
| return np.exp(2j * np.pi * j_idx * k_idx / dim) / np.sqrt(dim)
|
|
|
|
|
| class TestQft:
|
|
|
| @pytest.mark.parametrize('n_qubits', [1, 2, 3, 4])
|
| def test_matches_brute_force_dft_matrix(self, n_qubits):
|
| dim = 2 ** n_qubits
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| M = _dft_matrix(dim)
|
| for j in range(dim):
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| sim = DenseSVSimulator(n_qubits, use_gpu=False, use_float32=False)
|
| init = np.zeros(dim, dtype=complex)
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| init[j] = 1.0
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| sim.set_initial_state(init)
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| sim.run_circuit(qft(n_qubits))
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| got = sim.get_statevector()
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| assert np.max(np.abs(got - M[j])) < 1e-9
|
|
|
| def test_qft_of_zero_state_is_uniform_superposition(self):
|
| n_qubits = 3
|
| sim = DenseSVSimulator(n_qubits, use_gpu=False, use_float32=False)
|
| sim.run_circuit(qft(n_qubits))
|
| probs = sim.get_probabilities()
|
| assert np.allclose(probs, 1.0 / 2 ** n_qubits, atol=1e-9)
|
|
|
| def test_round_trip_qft_and_inverse_recovers_original_state(self):
|
| n_qubits = 3
|
| dim = 2 ** n_qubits
|
| rng = np.random.default_rng(0)
|
| psi0 = rng.normal(size=dim) + 1j * rng.normal(size=dim)
|
| psi0 /= np.linalg.norm(psi0)
|
|
|
| sim = DenseSVSimulator(n_qubits, use_gpu=False, use_float32=False)
|
| sim.set_initial_state(psi0.copy())
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| sim.run_circuit(qft(n_qubits) + qft(n_qubits, inverse=True))
|
| assert np.max(np.abs(sim.get_statevector() - psi0)) < 1e-9
|
|
|
| def test_without_swaps_differs_from_with_swaps(self):
|
| assert qft(3, do_swaps=False) != qft(3, do_swaps=True)
|
| assert qft(3, do_swaps=False) == qft(3, do_swaps=True)[:-1]
|
|
|
| def test_rejects_fewer_than_one_qubit(self):
|
| with pytest.raises(ValueError):
|
| qft(0)
|
|
|
