def test_bitstring_cost(self):
"Check the bitstring sampling function"
vqa = VQA(num_qubits=1, cost_method="BITSTRING")
vqa.add_block(VQABlock(qutip.sigmax()))
# target the |1> state by giving the "1" string a cost of 0
vqa.cost_func = lambda s: 1 - int(s)
res = vqa.optimize_parameters(initial=[np.pi / 2 + 1e-3])
assert res.get_top_bitstring() == "|1>"
def test_layer_by_layer(self):
"""
tests trivial optimization going layer-by-layer
"""
vqa = VQA(num_qubits=1, cost_method="STATE", num_layers=4)
block = VQABlock(qutip.sigmax())
vqa.add_block(block)
vqa.cost_func = lambda s: 1 - s.overlap(qutip.basis(2, 1)).real
res = vqa.optimize_parameters(
initial=[np.pi / 2, 0, 0, 0], layer_by_layer=True
)
assert res.get_top_bitstring() == "|1>"
def test_trivial_optimization(self):
"""
tests trivial optimization case where the initial conditinos
are already optimal for the problem
"""
block = VQABlock(qutip.sigmax())
# test the STATE type of cost function
vqa = VQA(num_qubits=1, cost_method="STATE")
vqa.add_block(block)
# try to reach the |1> state from the |0> state
vqa.cost_func = lambda s: 1 - s.overlap(qutip.basis(2, 1)).real
res = vqa.optimize_parameters(initial=[np.pi / 2])
assert res.get_top_bitstring() == "|1>"
def test_plot(self, todo):
"""
Check plotting function returns without error
"""
# Only test on environments that have the matplotlib dependency
try:
import matplotlib.pyplot as plt
except Exception:
return True
vqa = VQA(num_qubits=4, num_layers=1, cost_method="STATE")
for i in range(4):
vqa.add_block(VQABlock("X", targets=[i]))
vqa.cost_func = lambda s: 0
res = vqa.optimize_parameters()
res.plot(top_ten=todo, display=False)