def test_expand(self):
"""Test expand method."""
rho0, rho1 = np.diag([1, 0]), np.diag([0, 1])
rho_init = DensityMatrix(np.kron(rho0, rho0))
chan1 = Kraus(self.UI)
chan2 = Kraus(self.UX)
# X \otimes I
chan = chan1.expand(chan2)
rho_targ = DensityMatrix(np.kron(rho1, rho0))
self.assertEqual(chan.dim, (4, 4))
self.assertEqual(rho_init @ chan, rho_targ)
# I \otimes X
chan = chan2.expand(chan1)
rho_targ = DensityMatrix(np.kron(rho0, rho1))
self.assertEqual(chan.dim, (4, 4))
self.assertEqual(rho_init @ chan, rho_targ)
# Completely depolarizing
chan_dep = Kraus(self.depol_kraus(1))
chan = chan_dep.expand(chan_dep)
rho_targ = DensityMatrix(np.diag([1, 1, 1, 1]) / 4)
self.assertEqual(chan.dim, (4, 4))
self.assertEqual(rho_init @ chan, rho_targ)
syndrome_op = Kraus(job.result().get_unitary())
# Initialize fidelity simulation parameters
p_error = [0.05 * i for i in range(11)]
f1 = []
f2 = []
# Evolve initial state
for p in p_error:
# Build noise channel
bit_flip_channel = Kraus([[[0, np.sqrt(p)], [np.sqrt(p), 0]],
[[np.sqrt(1 - p), 0], [0, np.sqrt(1 - p)]]])
bit_flip_channel = bit_flip_channel.tensor(bit_flip_channel).tensor(
bit_flip_channel)
bit_flip_channel = bit_flip_channel.expand(Kraus(np.eye(2))).expand(
Kraus(np.eye(2)))
# Apply channels
corrupted_state = DensityMatrix(init_state.evolve(bit_flip_channel))
corrected_state = DensityMatrix(corrupted_state.evolve(syndrome_op))
corrected_state = DensityMatrix(corrected_state.evolve(
qecc.correction_ckt))
# Trace out syndrome
ini = DensityMatrix(partial_trace(init_state, [3, 4]))
corrupted_state = DensityMatrix(partial_trace(corrupted_state, [3, 4]))
corrected_state = DensityMatrix(partial_trace(corrected_state, [3, 4]))
# Record results
f1.append(state_fidelity(ini, corrupted_state))
f2.append(state_fidelity(ini, corrected_state))
