def test_kraus_channel_repr():
# This is equivalent to an X-basis measurement.
ops = [
np.array([[1, 1], [1, 1]], dtype=np.complex64) * 0.5,
np.array([[1, -1], [-1, 1]], dtype=np.complex64) * 0.5,
]
x_meas = cirq.KrausChannel(ops, key='x_meas')
assert (repr(x_meas) == """\
cirq.KrausChannel(kraus_ops=[\
np.array([[(0.5+0j), (0.5+0j)], [(0.5+0j), (0.5+0j)]], dtype=np.complex64), \
np.array([[(0.5+0j), (-0.5+0j)], [(-0.5+0j), (0.5+0j)]], dtype=np.complex64)], \
key='x_meas')""")
def test_kraus_channel_str():
# This is equivalent to an X-basis measurement.
ops = [
np.array([[1, 1], [1, 1]]) * 0.5,
np.array([[1, -1], [-1, 1]]) * 0.5
]
x_meas = cirq.KrausChannel(ops)
assert (str(x_meas) == """KrausChannel([array([[0.5, 0.5],
[0.5, 0.5]]), array([[ 0.5, -0.5],
[-0.5, 0.5]])])""")
x_meas_keyed = cirq.KrausChannel(ops, key='x_meas')
assert (str(x_meas_keyed) == """KrausChannel([array([[0.5, 0.5],
[0.5, 0.5]]), array([[ 0.5, -0.5],
[-0.5, 0.5]])], key=x_meas)""")
def test_ops_mismatch_fails():
op2 = np.zeros((4, 4))
op2[1][1] = 1
ops = [np.array([[1, 0], [0, 0]]), op2]
with pytest.raises(ValueError, match='Inconsistent Kraus operator shapes'):
_ = cirq.KrausChannel(kraus_ops=ops, key='m')
def test_validate():
# Not quite CPTP.
ops = [
np.array([[1, 0], [0, 0]]),
np.array([[0, 0], [0, 0.9]]),
]
with pytest.raises(ValueError, match='CPTP map'):
_ = cirq.KrausChannel(kraus_ops=ops, key='m', validate=True)
def test_nonqubit_kraus_ops_fails():
ops = [
np.array([[1, 0, 0], [0, 0, 0]]),
np.array([[0, 0, 0], [0, 1, 0]]),
]
with pytest.raises(ValueError, match='Input Kraus ops'):
_ = cirq.KrausChannel(kraus_ops=ops, key='m')
def test_measured_channel():
# This behaves like an X-basis measurement.
kc = cirq.KrausChannel(kraus_ops=(np.array([[1, 1], [1, 1]]) * 0.5,
np.array([[1, -1], [-1, 1]]) * 0.5),
key='m')
q0 = cirq.LineQubit(0)
circuit = cirq.Circuit(cirq.H(q0), kc.on(q0))
sim = cirq.Simulator(seed=0)
results = sim.run(circuit, repetitions=100)
assert results.histogram(key='m') == {0: 100}
def test_kraus_channel_equality():
dp_pt1 = cirq.depolarize(0.1)
dp_pt2 = cirq.depolarize(0.2)
kc_a1 = cirq.KrausChannel.from_channel(dp_pt1, key='a')
kc_a2 = cirq.KrausChannel.from_channel(dp_pt2, key='a')
kc_b1 = cirq.KrausChannel.from_channel(dp_pt1, key='b')
# Even if their effect is the same, KrausChannels are not treated as equal
# to other channels defined in Cirq.
assert kc_a1 != dp_pt1
assert kc_a1 != kc_a2
assert kc_a1 != kc_b1
assert kc_a2 != kc_b1
ops = [np.array([[1, 0], [0, 0]]), np.array([[0, 0], [0, 1]])]
x_meas = cirq.KrausChannel(ops)
ops_inv = list(reversed(ops))
x_meas_inv = cirq.KrausChannel(ops_inv)
# Even though these have the same effect on the circuit, their measurement
# behavior differs, so they are considered non-equal.
assert x_meas != x_meas_inv
def test_assert_consistent_channel_tolerances():
# This channel is off by 1e-5 from the identity matrix in the consistency condition.
channel = cirq.KrausChannel(
kraus_ops=(np.array([[0, np.sqrt(1 - 1e-5)], [0, 0]]),
np.array([[1, 0], [0, 0]])))
# We are comparing to identity, so rtol is same as atol for non-zero entries.
cirq.testing.assert_consistent_channel(channel, rtol=1e-5, atol=0)
with pytest.raises(AssertionError):
cirq.testing.assert_consistent_channel(channel, rtol=1e-6, atol=0)
cirq.testing.assert_consistent_channel(channel, rtol=0, atol=1e-5)
with pytest.raises(AssertionError):
cirq.testing.assert_consistent_channel(channel, rtol=0, atol=1e-6)
def test_kraus_channel_from_kraus():
q0 = cirq.LineQubit(0)
# This is equivalent to an X-basis measurement.
ops = [
np.array([[1, 1], [1, 1]]) * 0.5,
np.array([[1, -1], [-1, 1]]) * 0.5
]
x_meas = cirq.KrausChannel(ops, key='x_meas')
assert cirq.measurement_key_name(x_meas) == 'x_meas'
circuit = cirq.Circuit(cirq.H(q0), x_meas.on(q0))
sim = cirq.Simulator(seed=0)
results = sim.simulate(circuit)
assert 'x_meas' in results.measurements
assert results.measurements['x_meas'] == 0
def test_qubits_should_be_defined_for_operations():
args = DummyActOnArgs()
with pytest.raises(ValueError, match='Calls to act_on should'):
cirq.act_on(cirq.KrausChannel([np.array([[1, 0], [0, 0]])]),
args,
qubits=None)
def test_empty_ops_fails():
ops = []
with pytest.raises(ValueError, match='must have at least one operation'):
_ = cirq.KrausChannel(kraus_ops=ops, key='m')
def test_assert_consistent_channel_invalid():
channel = cirq.KrausChannel(kraus_ops=(np.array([[1, 1], [0, 0]]),
np.array([[1, 0], [0, 0]])))
with pytest.raises(AssertionError, match=r"cirq.KrausChannel.*2 1"):
cirq.testing.assert_consistent_channel(channel)
def test_assert_consistent_channel_valid():
channel = cirq.KrausChannel(kraus_ops=(np.array([[0, 1], [0, 0]]),
np.array([[1, 0], [0, 0]])))
cirq.testing.assert_consistent_channel(channel)
def test_qubits_should_be_defined_for_operations():
state = DummySimulationState()
with pytest.raises(ValueError, match='Calls to act_on should'):
cirq.act_on(cirq.KrausChannel([np.array([[1, 0], [0, 0]])]), state, qubits=None)
