mirror of
https://github.com/blackboxprogramming/quantum-math-lab.git
synced 2026-03-17 05:57:18 -05:00
5e7b36c250
Co-authored-by: blackboxprogramming <118287761+blackboxprogramming@users.noreply.github.com>
333 lines
13 KiB
Python
333 lines
13 KiB
Python
"""Comprehensive test suite for the quantum circuit simulator.
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Tests cover single-qubit gates, multi-qubit entanglement, measurement
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statistics, custom unitaries, error handling, and edge cases.
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"""
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import numpy as np
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import pytest
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from quantum_simulator import MeasurementResult, QuantumCircuit
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# ── Single-qubit gates ──────────────────────────────────────────────────────
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class TestHadamard:
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def test_creates_equal_superposition(self):
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circuit = QuantumCircuit(1)
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circuit.hadamard(0)
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probs = circuit.probabilities()
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assert probs["0"] == pytest.approx(0.5, abs=1e-8)
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assert probs["1"] == pytest.approx(0.5, abs=1e-8)
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def test_double_hadamard_returns_to_ground(self):
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"""H*H = I: applying Hadamard twice should return to |0>."""
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circuit = QuantumCircuit(1)
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circuit.hadamard(0)
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circuit.hadamard(0)
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probs = circuit.probabilities()
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assert probs["0"] == pytest.approx(1.0, abs=1e-8)
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assert probs["1"] == pytest.approx(0.0, abs=1e-8)
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def test_hadamard_on_second_qubit(self):
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circuit = QuantumCircuit(2)
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circuit.hadamard(1)
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probs = circuit.probabilities()
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assert probs["00"] == pytest.approx(0.5, abs=1e-8)
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assert probs["01"] == pytest.approx(0.5, abs=1e-8)
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assert probs["10"] == pytest.approx(0.0, abs=1e-8)
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assert probs["11"] == pytest.approx(0.0, abs=1e-8)
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class TestPauliX:
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def test_flips_ground_state(self):
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circuit = QuantumCircuit(1)
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circuit.pauli_x(0)
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probs = circuit.probabilities()
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assert probs["1"] == pytest.approx(1.0)
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assert probs["0"] == pytest.approx(0.0)
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def test_double_x_returns_to_ground(self):
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"""X*X = I: flipping twice returns to |0>."""
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circuit = QuantumCircuit(1)
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circuit.pauli_x(0)
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circuit.pauli_x(0)
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probs = circuit.probabilities()
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assert probs["0"] == pytest.approx(1.0)
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def test_x_on_specific_qubit(self):
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circuit = QuantumCircuit(3)
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circuit.pauli_x(1)
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probs = circuit.probabilities()
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assert probs["010"] == pytest.approx(1.0)
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# ── Two-qubit gates (CNOT) ─────────────────────────────────────────────────
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class TestCNOT:
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def test_creates_bell_state(self):
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circuit = QuantumCircuit(2)
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circuit.hadamard(0)
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circuit.cnot(0, 1)
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probs = circuit.probabilities()
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assert probs["00"] == pytest.approx(0.5, abs=1e-8)
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assert probs["11"] == pytest.approx(0.5, abs=1e-8)
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assert probs["01"] == pytest.approx(0.0, abs=1e-8)
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assert probs["10"] == pytest.approx(0.0, abs=1e-8)
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def test_cnot_with_control_zero(self):
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"""CNOT does nothing when control qubit is |0>."""
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circuit = QuantumCircuit(2)
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circuit.cnot(0, 1)
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probs = circuit.probabilities()
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assert probs["00"] == pytest.approx(1.0)
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def test_cnot_with_control_one(self):
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"""CNOT flips target when control qubit is |1>."""
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circuit = QuantumCircuit(2)
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circuit.pauli_x(0)
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circuit.cnot(0, 1)
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probs = circuit.probabilities()
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assert probs["11"] == pytest.approx(1.0)
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def test_cnot_same_qubit_raises(self):
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circuit = QuantumCircuit(2)
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with pytest.raises(ValueError, match="different"):
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circuit.cnot(0, 0)
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def test_three_qubit_ghz_state(self):
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"""Create a 3-qubit GHZ state: (|000> + |111>) / sqrt(2)."""
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circuit = QuantumCircuit(3)
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circuit.hadamard(0)
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circuit.cnot(0, 1)
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circuit.cnot(0, 2)
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probs = circuit.probabilities()
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assert probs["000"] == pytest.approx(0.5, abs=1e-8)
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assert probs["111"] == pytest.approx(0.5, abs=1e-8)
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for key in ["001", "010", "011", "100", "101", "110"]:
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assert probs[key] == pytest.approx(0.0, abs=1e-8)
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# ── Custom unitaries ───────────────────────────────────────────────────────
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class TestCustomUnitary:
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def test_pauli_z_gate(self):
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"""Z gate: |0> -> |0>, |1> -> -|1>. Probabilities unchanged."""
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Z = np.array([[1, 0], [0, -1]], dtype=np.complex128)
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circuit = QuantumCircuit(1)
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circuit.hadamard(0)
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circuit.apply_custom(Z, [0])
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# H then Z on |0> gives (|0> - |1>)/sqrt(2) — same probabilities
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probs = circuit.probabilities()
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assert probs["0"] == pytest.approx(0.5, abs=1e-8)
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assert probs["1"] == pytest.approx(0.5, abs=1e-8)
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def test_pauli_z_then_hadamard(self):
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"""H*Z*H|0> = X|0> = |1>."""
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Z = np.array([[1, 0], [0, -1]], dtype=np.complex128)
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circuit = QuantumCircuit(1)
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circuit.hadamard(0)
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circuit.apply_custom(Z, [0])
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circuit.hadamard(0)
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probs = circuit.probabilities()
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assert probs["1"] == pytest.approx(1.0, abs=1e-8)
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def test_identity_gate(self):
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identity = np.eye(2, dtype=np.complex128)
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circuit = QuantumCircuit(1)
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circuit.hadamard(0)
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circuit.apply_custom(identity, [0])
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probs = circuit.probabilities()
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assert probs["0"] == pytest.approx(0.5, abs=1e-8)
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def test_swap_gate(self):
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"""SWAP gate exchanges two qubits."""
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SWAP = np.array([
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[1, 0, 0, 0],
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[0, 0, 1, 0],
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[0, 1, 0, 0],
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[0, 0, 0, 1],
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], dtype=np.complex128)
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circuit = QuantumCircuit(2)
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circuit.pauli_x(0) # |10>
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circuit.apply_custom(SWAP, [0, 1])
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probs = circuit.probabilities()
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assert probs["01"] == pytest.approx(1.0)
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def test_wrong_dimension_raises(self):
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circuit = QuantumCircuit(1)
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with pytest.raises(ValueError, match="dimension"):
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circuit.apply_custom(np.eye(4), [0])
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# ── Measurement ─────────────────────────────────────────────────────────────
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class TestMeasurement:
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def test_partial_measurement_collapses_state(self):
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rng = np.random.default_rng(seed=7)
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circuit = QuantumCircuit(2)
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circuit.hadamard(0)
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circuit.cnot(0, 1)
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result = circuit.measure(qubits=[0], shots=1, rng=rng)
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assert result.total_shots() == 1
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probs = circuit.probabilities()
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if result.counts.get("0", 0) == 1:
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assert probs["00"] == pytest.approx(1.0)
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else:
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assert probs["11"] == pytest.approx(1.0)
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def test_measurement_statistics(self):
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"""Many shots of a fair superposition should be ~50/50."""
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rng = np.random.default_rng(seed=42)
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circuit = QuantumCircuit(1)
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circuit.hadamard(0)
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result = circuit.measure(shots=1000, rng=rng)
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zero_frac = result.counts.get("0", 0) / 1000
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assert zero_frac == pytest.approx(0.5, abs=0.06)
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def test_deterministic_measurement(self):
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"""Measuring |0> always gives 0."""
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circuit = QuantumCircuit(1)
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result = circuit.measure(shots=100, rng=np.random.default_rng(0))
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assert result.counts.get("0", 0) == 100
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def test_measurement_result_most_likely(self):
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result = MeasurementResult(counts={"00": 10, "01": 5, "10": 3, "11": 82})
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assert result.most_likely() == "11"
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assert result.total_shots() == 100
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def test_zero_shots_raises(self):
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circuit = QuantumCircuit(1)
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with pytest.raises(ValueError, match="positive"):
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circuit.measure(shots=0)
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# ── Error handling ──────────────────────────────────────────────────────────
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class TestErrorHandling:
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def test_zero_qubits_raises(self):
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with pytest.raises(ValueError, match="at least one"):
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QuantumCircuit(0)
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def test_negative_qubits_raises(self):
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with pytest.raises(ValueError):
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QuantumCircuit(-1)
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def test_qubit_index_out_of_range(self):
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circuit = QuantumCircuit(2)
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with pytest.raises(IndexError):
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circuit.hadamard(5)
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def test_duplicate_qubits_in_custom(self):
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circuit = QuantumCircuit(2)
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with pytest.raises(ValueError, match="distinct"):
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circuit.apply_custom(np.eye(4), [0, 0])
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# ── Probabilities sum to 1 ─────────────────────────────────────────────────
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class TestProbabilityNormalization:
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def test_initial_state_normalized(self):
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circuit = QuantumCircuit(3)
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probs = circuit.probabilities()
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assert sum(probs.values()) == pytest.approx(1.0)
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def test_after_gates_normalized(self):
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circuit = QuantumCircuit(3)
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circuit.hadamard(0)
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circuit.hadamard(1)
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circuit.cnot(0, 2)
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probs = circuit.probabilities()
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assert sum(probs.values()) == pytest.approx(1.0)
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def test_partial_probabilities_normalized(self):
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circuit = QuantumCircuit(3)
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circuit.hadamard(0)
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circuit.hadamard(1)
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probs = circuit.probabilities(qubits=[0])
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assert sum(probs.values()) == pytest.approx(1.0)
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# ── Additional coverage ────────────────────────────────────────────────────
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class TestEmptyQubits:
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def test_probabilities_empty_list_returns_full_distribution(self):
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"""probabilities(qubits=[]) takes the early-return path and matches full dist."""
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circuit = QuantumCircuit(2)
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circuit.hadamard(0)
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probs_empty = circuit.probabilities(qubits=[])
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probs_full = circuit.probabilities()
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for key in probs_full:
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assert probs_empty[key] == pytest.approx(probs_full[key], abs=1e-8)
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def test_measure_empty_qubits_collapses_to_single_basis_state(self):
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"""measure(qubits=[]) collapses the full state; _collapse_state empty path."""
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rng = np.random.default_rng(seed=0)
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circuit = QuantumCircuit(2)
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circuit.hadamard(0)
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circuit.cnot(0, 1)
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result = circuit.measure(qubits=[], shots=1, rng=rng)
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assert result.total_shots() == 1
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probs = circuit.probabilities()
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nonzero = [v for v in probs.values() if v > 1e-9]
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assert len(nonzero) == 1
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assert nonzero[0] == pytest.approx(1.0, abs=1e-8)
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class TestNonSquareUnitary:
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def test_non_square_matrix_raises(self):
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"""A non-square matrix must raise ValueError (covers the ndim/shape check)."""
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circuit = QuantumCircuit(1)
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with pytest.raises(ValueError, match="square"):
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circuit.apply_custom(np.zeros((2, 3), dtype=complex), [0])
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class TestMostLikelyTieBreaking:
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def test_tie_broken_by_lexicographically_smallest(self):
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"""Ties in counts must resolve to the lexicographically smallest string."""
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result = MeasurementResult(counts={"01": 5, "10": 5})
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assert result.most_likely() == "01"
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def test_tie_three_way(self):
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result = MeasurementResult(counts={"11": 3, "00": 3, "01": 3})
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assert result.most_likely() == "00"
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class TestAdditionalCircuits:
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def test_pauli_y_gate(self):
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"""Pauli-Y: Y|0⟩ = i|1⟩, so probability of measuring |1⟩ is 1."""
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Y = np.array([[0, -1j], [1j, 0]], dtype=np.complex128)
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circuit = QuantumCircuit(1)
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circuit.apply_custom(Y, [0])
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probs = circuit.probabilities()
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assert probs["0"] == pytest.approx(0.0, abs=1e-8)
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assert probs["1"] == pytest.approx(1.0, abs=1e-8)
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def test_five_qubit_ghz_state(self):
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"""5-qubit GHZ state: equal superposition of |00000⟩ and |11111⟩."""
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circuit = QuantumCircuit(5)
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circuit.hadamard(0)
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for i in range(1, 5):
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circuit.cnot(0, i)
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probs = circuit.probabilities()
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assert probs["00000"] == pytest.approx(0.5, abs=1e-8)
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assert probs["11111"] == pytest.approx(0.5, abs=1e-8)
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for key, val in probs.items():
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if key not in ("00000", "11111"):
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assert val == pytest.approx(0.0, abs=1e-8)
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def test_bell_state_qubit1_collapses_qubit0(self):
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"""Measuring qubit 0 of a Bell state collapses qubit 1 to the same value."""
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circuit = QuantumCircuit(2)
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circuit.hadamard(0)
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circuit.cnot(0, 1)
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rng = np.random.default_rng(seed=999)
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result = circuit.measure(qubits=[0], shots=1, rng=rng)
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outcome = result.most_likely()
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probs = circuit.probabilities()
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if outcome == "0":
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assert probs["00"] == pytest.approx(1.0, abs=1e-8)
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else:
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assert probs["11"] == pytest.approx(1.0, abs=1e-8)
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