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Author: JavierMartinAlonso1980

test/validation_tools.py

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+# test/validation_tools.py
+"""
+Injection-Test Validation Tools
+================================
+Shared helpers for all injection-style tests:
+- TMST Gaussian entanglement (point 4.2 / 4.5)
+- Qiskit 2-qubit Bell vs noise (point 4.1 / 4.2)
+
+These functions implement the "inject known signal vs pure noise,
+then verify metrics respond correctly" pattern described in the
+BasQ conversations.
+"""
+
+from __future__ import annotations
+import numpy as np
+import numpy.typing as npt
+
+# ─────────────────────────────────────────────
+# TMST injection helpers
+# ─────────────────────────────────────────────
+
+def make_tmst_signal(
+    T: float,
+    delta_above: float = 0.3,
+    omega: float = 1.0,
+) -> tuple[float, float]:
+    """
+    Return (r_signal, n_bar) for a squeezing value ABOVE the threshold.
+    'delta_above' sets how far above r_c we place the signal.
+    """
+    from src.seemps_vortex.tmst_threshold import bose_einstein, critical_squeezing
+    n_bar = float(bose_einstein(np.array([T]), omega=omega)[0])
+    rc = float(critical_squeezing(n_bar))
+    return rc + delta_above, n_bar
+
+
+def make_tmst_noise(
+    T: float,
+    alpha_below: float = 0.5,
+    omega: float = 1.0,
+) -> tuple[float, float]:
+    """
+    Return (r_noise, n_bar) for a squeezing value BELOW the threshold.
+    'alpha_below' is the fraction of r_c to use (< 1 → separable).
+    """
+    from src.seemps_vortex.tmst_threshold import bose_einstein, critical_squeezing
+    n_bar = float(bose_einstein(np.array([T]), omega=omega)[0])
+    rc = float(critical_squeezing(n_bar))
+    return alpha_below * rc, n_bar
+
+
+# ─────────────────────────────────────────────
+# Qiskit 2-qubit injection helpers
+# ─────────────────────────────────────────────
+
+def bell_state_circuit():
+    """
+    Returns a 2-qubit QuantumCircuit preparing |Φ+⟩ = (|00⟩+|11⟩)/√2.
+    This is the 'maximum entanglement' injection signal.
+    Requires qiskit.
+    """
+    from qiskit import QuantumCircuit
+    qc = QuantumCircuit(2)
+    qc.h(0)
+    qc.cx(0, 1)
+    return qc
+
+
+def product_noise_circuit(seed: int | None = None):
+    """
+    Returns a 2-qubit QuantumCircuit with independent random RX rotations.
+    This is the 'no entanglement / pure noise' injection.
+    """
+    from qiskit import QuantumCircuit
+    rng = np.random.default_rng(seed)
+    qc = QuantumCircuit(2)
+    qc.rx(rng.uniform(0, np.pi), 0)
+    qc.rx(rng.uniform(0, np.pi), 1)
+    return qc
+
+
+def log_negativity_from_statevector(qc) -> float:
+    """
+    Compute log-negativity E_N for a pure 2-qubit state via partial transpose.
+    Works directly on a QuantumCircuit (no measurement needed).
+    """
+    from qiskit.quantum_info import Statevector
+    sv = Statevector.from_instruction(qc)
+    rho = np.outer(sv.data, sv.data.conj())
+
+    # Partial transpose on qubit 1 (reshape → swap indices → reshape back)
+    rho_TB = rho.reshape(2, 2, 2, 2).transpose(0, 3, 2, 1).reshape(4, 4)
+    evals = np.linalg.eigvalsh(rho_TB)
+    negativity = np.sum(np.abs(evals[evals < 0.0]))
+    EN = np.log2(2.0 * negativity + 1.0)
+    return float(max(0.0, EN))
+
+
+def state_fidelity_to_bell(qc) -> float:
+    """
+    Fidelity of the state in qc with the ideal Bell state |Φ+⟩.
+    """
+    from qiskit.quantum_info import Statevector, state_fidelity
+    ideal = Statevector.from_instruction(bell_state_circuit())
+    actual = Statevector.from_instruction(qc)
+    return float(state_fidelity(ideal, actual))