def test_measure(self):
# First, test measurement of a system in a pure state
STATE = '01010'
N = len(STATE)
q = QubitSystem(N, int('0b' + STATE, 2))
self.assertEqual(q.measure(), int('0b' + STATE, 2))
self.assertEqual(q.smeasure(), STATE)
for i in range(N):
self.assertEqual(q.measure(i + 1), int(STATE[i]))
# Test probabilistic measurement: repeatedly measure superpositions of
# basis states and test that the outcome varies randomly.
N = 2
NTRIALS = 100
# number of 1's in the first and second bit, respectively
nsuccess1 = 0
nsuccess2 = 0
for i in range(NTRIALS):
q = QubitSystem(N) # set the qubits to |00>
hadamard_gate(N) * q # equal superposition of four basis states
nsuccess1 += q.measure(1)
nsuccess2 += q.measure(2)
# Test that repeated measurement gives the same result
state = q.measure()
self.assertEqual(q.measure(), state)
self.assertEqual(q.measure(), state)
# Test that the number of 1's that appeared in the first and second
# qubits is approximately half the total (within approx. 99% confidence
# interval)
CUTOFF = NTRIALS * 0.15
self.assertTrue(abs(nsuccess1 - NTRIALS / 2.) < CUTOFF)
self.assertTrue(abs(nsuccess2 - NTRIALS / 2.) < CUTOFF)
