def test_mutual_information(self):
input_state = np.array([[0.5, 0.25, 0.75, 1],
[1, 0, 1, 0],
[0.5, 0.5, 0.5, 0.5],
[0, 1, 0, 1]])
res = mutual_information(input_state, 2)
self.assertAlmostEqual(-0.15821825498448047, res)
def discord(rho, qubit=0):
"""
The quantum discord between two qubits
Quantum discord is defined in Phys. Rev. Lett. 88, 017901 (2001).
We use base 2 for log.
Args:
rho (Array): a two-qubit density operator
qubit (int): 0 or 1, the qubit on which the measurement is done (default 0)
Return:
float: quantum discord, between [0, 1]
"""
return (mutual_information(rho, 2)/np.log(2) - classical_correlation(rho, qubit=qubit))