Rename cirq.channel to cirq.kraus (#4195)

Author: viathor

cirq-core/cirq/__init__.py

@@ -479,6 +479,7 @@
     definitely_commutes,
     equal_up_to_global_phase,
     has_channel,
+    has_kraus,
     has_mixture,
     has_stabilizer_effect,
     has_unitary,
@@ -487,6 +488,7 @@
     is_parameterized,
     JsonResolver,
     json_serializable_dataclass,
+    kraus,
     measurement_key,
     measurement_keys,
     mixture,

cirq-core/cirq/contrib/quimb/density_matrix.py

@@ -84,7 +84,7 @@ def circuit_to_density_matrix_tensors(
 
     Args:
         circuit: The circuit containing operations that support the
-            cirq.unitary() or cirq.channel() protocols.
+            cirq.unitary() or cirq.kraus() protocols.
         qubits: The qubits in the circuit.
 
     Returns:
@@ -161,8 +161,8 @@ def _positions(mi, qubits):
                         tags={f'Q{len(op.qubits)}', f'i{mi + 1}b', _qpos_tag(op.qubits)},
                     )
                 )
-            elif cirq.has_channel(op):
-                K = np.asarray(cirq.channel(op), dtype=np.complex128)
+            elif cirq.has_kraus(op):
+                K = np.asarray(cirq.kraus(op), dtype=np.complex128)
                 kraus_inds = [f'k{kraus_frontier}']
                 tensors.append(
                     qtn.Tensor(

cirq-core/cirq/ops/common_channels_test.py

@@ -58,10 +58,10 @@ def assert_mixtures_equal(actual, expected):
 def test_asymmetric_depolarizing_channel():
     d = cirq.asymmetric_depolarize(0.1, 0.2, 0.3)
     np.testing.assert_almost_equal(
-        cirq.channel(d),
+        cirq.kraus(d),
         (np.sqrt(0.4) * np.eye(2), np.sqrt(0.1) * X, np.sqrt(0.2) * Y, np.sqrt(0.3) * Z),
     )
-    assert cirq.has_channel(d)
+    assert cirq.has_kraus(d)
 
 
 def test_asymmetric_depolarizing_mixture():
@@ -134,21 +134,21 @@ def test_asymmetric_depolarizing_channel_text_diagram():
 def test_depolarizing_channel():
     d = cirq.depolarize(0.3)
     np.testing.assert_almost_equal(
-        cirq.channel(d),
+        cirq.kraus(d),
         (
             np.sqrt(0.7) * np.eye(2),
             np.sqrt(0.1) * X,
             np.sqrt(0.1) * Y,
             np.sqrt(0.1) * Z,
         ),
     )
-    assert cirq.has_channel(d)
+    assert cirq.has_kraus(d)
 
 
 def test_depolarizing_channel_two_qubits():
     d = cirq.depolarize(0.15, n_qubits=2)
     np.testing.assert_almost_equal(
-        cirq.channel(d),
+        cirq.kraus(d),
         (
             np.sqrt(0.85) * np.eye(4),
             np.sqrt(0.01) * np.kron(np.eye(2), X),
@@ -168,7 +168,7 @@ def test_depolarizing_channel_two_qubits():
             np.sqrt(0.01) * np.kron(Z, Z),
         ),
     )
-    assert cirq.has_channel(d)
+    assert cirq.has_kraus(d)
 
     assert d.num_qubits() == 2
     cirq.testing.assert_has_diagram(
@@ -310,15 +310,15 @@ def test_depolarizing_channel_text_diagram_two_qubits():
 def test_generalized_amplitude_damping_channel():
     d = cirq.generalized_amplitude_damp(0.1, 0.3)
     np.testing.assert_almost_equal(
-        cirq.channel(d),
+        cirq.kraus(d),
         (
             np.sqrt(0.1) * np.array([[1.0, 0.0], [0.0, np.sqrt(1.0 - 0.3)]]),
             np.sqrt(0.1) * np.array([[0.0, np.sqrt(0.3)], [0.0, 0.0]]),
             np.sqrt(0.9) * np.array([[np.sqrt(1.0 - 0.3), 0.0], [0.0, 1.0]]),
             np.sqrt(0.9) * np.array([[0.0, 0.0], [np.sqrt(0.3), 0.0]]),
         ),
     )
-    assert cirq.has_channel(d)
+    assert cirq.has_kraus(d)
     assert not cirq.has_mixture(d)
 
 
@@ -376,13 +376,13 @@ def test_generalized_amplitude_damping_channel_text_diagram():
 def test_amplitude_damping_channel():
     d = cirq.amplitude_damp(0.3)
     np.testing.assert_almost_equal(
-        cirq.channel(d),
+        cirq.kraus(d),
         (
             np.array([[1.0, 0.0], [0.0, np.sqrt(1.0 - 0.3)]]),
             np.array([[0.0, np.sqrt(0.3)], [0.0, 0.0]]),
         ),
     )
-    assert cirq.has_channel(d)
+    assert cirq.has_kraus(d)
     assert not cirq.has_mixture(d)
 
 
@@ -432,22 +432,22 @@ def test_amplitude_damping_channel_text_diagram():
 def test_reset_channel():
     r = cirq.reset(cirq.LineQubit(0))
     np.testing.assert_almost_equal(
-        cirq.channel(r), (np.array([[1.0, 0.0], [0.0, 0]]), np.array([[0.0, 1.0], [0.0, 0.0]]))
+        cirq.kraus(r), (np.array([[1.0, 0.0], [0.0, 0]]), np.array([[0.0, 1.0], [0.0, 0.0]]))
     )
-    assert cirq.has_channel(r)
+    assert cirq.has_kraus(r)
     assert not cirq.has_mixture(r)
     assert cirq.qid_shape(r) == (2,)
 
     r = cirq.reset(cirq.LineQid(0, dimension=3))
     np.testing.assert_almost_equal(
-        cirq.channel(r),
+        cirq.kraus(r),
         (
             np.array([[1, 0, 0], [0, 0, 0], [0, 0, 0]]),
             np.array([[0, 1, 0], [0, 0, 0], [0, 0, 0]]),
             np.array([[0, 0, 1], [0, 0, 0], [0, 0, 0]]),
         ),
     )  # yapf: disable
-    assert cirq.has_channel(r)
+    assert cirq.has_kraus(r)
     assert not cirq.has_mixture(r)
     assert cirq.qid_shape(r) == (3,)
 
@@ -508,13 +508,13 @@ def test_reset_act_on():
 def test_phase_damping_channel():
     d = cirq.phase_damp(0.3)
     np.testing.assert_almost_equal(
-        cirq.channel(d),
+        cirq.kraus(d),
         (
             np.array([[1.0, 0.0], [0.0, np.sqrt(1 - 0.3)]]),
             np.array([[0.0, 0.0], [0.0, np.sqrt(0.3)]]),
         ),
     )
-    assert cirq.has_channel(d)
+    assert cirq.has_kraus(d)
     assert not cirq.has_mixture(d)
 
 
@@ -564,9 +564,9 @@ def test_phase_damping_channel_text_diagram():
 def test_phase_flip_channel():
     d = cirq.phase_flip(0.3)
     np.testing.assert_almost_equal(
-        cirq.channel(d), (np.sqrt(1.0 - 0.3) * np.eye(2), np.sqrt(0.3) * Z)
+        cirq.kraus(d), (np.sqrt(1.0 - 0.3) * np.eye(2), np.sqrt(0.3) * Z)
     )
-    assert cirq.has_channel(d)
+    assert cirq.has_kraus(d)
 
 
 def test_phase_flip_mixture():
@@ -628,9 +628,9 @@ def test_phase_flip_channel_text_diagram():
 def test_bit_flip_channel():
     d = cirq.bit_flip(0.3)
     np.testing.assert_almost_equal(
-        cirq.channel(d), (np.sqrt(1.0 - 0.3) * np.eye(2), np.sqrt(0.3) * X)
+        cirq.kraus(d), (np.sqrt(1.0 - 0.3) * np.eye(2), np.sqrt(0.3) * X)
     )
-    assert cirq.has_channel(d)
+    assert cirq.has_kraus(d)
 
 
 def test_bit_flip_mixture():
@@ -734,9 +734,9 @@ def test_missing_prob_mass():
 def test_multi_asymmetric_depolarizing_channel():
     d = cirq.asymmetric_depolarize(error_probabilities={'II': 0.8, 'XX': 0.2})
     np.testing.assert_almost_equal(
-        cirq.channel(d), (np.sqrt(0.8) * np.eye(4), np.sqrt(0.2) * np.kron(X, X))
+        cirq.kraus(d), (np.sqrt(0.8) * np.eye(4), np.sqrt(0.2) * np.kron(X, X))
     )
-    assert cirq.has_channel(d)
+    assert cirq.has_kraus(d)
     np.testing.assert_equal(d._num_qubits_(), 2)
 
     with pytest.raises(ValueError, match="num_qubits should be 1"):

cirq-core/cirq/ops/gate_operation_test.py

@@ -249,11 +249,11 @@ def test_unitary():
 def test_channel():
     a = cirq.NamedQubit('a')
     op = cirq.bit_flip(0.5).on(a)
-    np.testing.assert_allclose(cirq.channel(op), cirq.channel(op.gate))
-    assert cirq.has_channel(op)
+    np.testing.assert_allclose(cirq.kraus(op), cirq.kraus(op.gate))
+    assert cirq.has_kraus(op)
 
-    assert cirq.channel(cirq.SingleQubitGate()(a), None) is None
-    assert not cirq.has_channel(cirq.SingleQubitGate()(a))
+    assert cirq.kraus(cirq.SingleQubitGate()(a), None) is None
+    assert not cirq.has_kraus(cirq.SingleQubitGate()(a))
 
 
 def test_measurement_key():

cirq-core/cirq/ops/measurement_gate_test.py

@@ -201,12 +201,12 @@ def test_measurement_gate_diagram():
 
 def test_measurement_channel():
     np.testing.assert_allclose(
-        cirq.channel(cirq.MeasurementGate(1)),
+        cirq.kraus(cirq.MeasurementGate(1)),
         (np.array([[1, 0], [0, 0]]), np.array([[0, 0], [0, 1]])),
     )
     # yapf: disable
     np.testing.assert_allclose(
-            cirq.channel(cirq.MeasurementGate(2)),
+            cirq.kraus(cirq.MeasurementGate(2)),
             (np.array([[1, 0, 0, 0],
                        [0, 0, 0, 0],
                        [0, 0, 0, 0],
@@ -224,7 +224,7 @@ def test_measurement_channel():
                        [0, 0, 0, 0],
                        [0, 0, 0, 1]])))
     np.testing.assert_allclose(
-            cirq.channel(cirq.MeasurementGate(2, qid_shape=(2, 3))),
+            cirq.kraus(cirq.MeasurementGate(2, qid_shape=(2, 3))),
             (np.diag([1, 0, 0, 0, 0, 0]),
              np.diag([0, 1, 0, 0, 0, 0]),
              np.diag([0, 0, 1, 0, 0, 0]),

cirq-core/cirq/ops/random_gate_channel.py

@@ -57,7 +57,7 @@ def _has_mixture_(self):
         return not self._is_parameterized_() and protocols.has_mixture(self.sub_gate)
 
     def _has_kraus_(self):
-        return not self._is_parameterized_() and protocols.has_channel(self.sub_gate)
+        return not self._is_parameterized_() and protocols.has_kraus(self.sub_gate)
 
     def _is_parameterized_(self) -> bool:
         return protocols.is_parameterized(self.probability) or protocols.is_parameterized(
@@ -94,7 +94,7 @@ def _kraus_(self):
         if self._is_parameterized_():
             return NotImplemented
 
-        channel = protocols.channel(self.sub_gate, None)
+        channel = protocols.kraus(self.sub_gate, None)
         if channel is None:
             return NotImplemented
 

cirq-core/cirq/ops/random_gate_channel_test.py

@@ -125,13 +125,13 @@ def num_qubits(self) -> int:
 def test_parameterized(resolve_fn):
     op = cirq.X.with_probability(sympy.Symbol('x'))
     assert cirq.is_parameterized(op)
-    assert not cirq.has_channel(op)
+    assert not cirq.has_kraus(op)
     assert not cirq.has_mixture(op)
 
     op2 = resolve_fn(op, {'x': 0.5})
     assert op2 == cirq.X.with_probability(0.5)
     assert not cirq.is_parameterized(op2)
-    assert cirq.has_channel(op2)
+    assert cirq.has_kraus(op2)
     assert cirq.has_mixture(op2)
 
 
@@ -158,7 +158,7 @@ def num_qubits(self) -> int:
 
 
 def assert_channel_sums_to_identity(val):
-    m = cirq.channel(val)
+    m = cirq.kraus(val)
     s = sum(np.conj(e.T) @ e for e in m)
     np.testing.assert_allclose(s, np.eye(np.product(cirq.qid_shape(val))), atol=1e-8)
 
@@ -168,14 +168,14 @@ class NoDetailsGate(cirq.Gate):
         def num_qubits(self) -> int:
             return 1
 
-    assert not cirq.has_channel(NoDetailsGate().with_probability(0.5))
-    assert cirq.channel(NoDetailsGate().with_probability(0.5), None) is None
-    assert cirq.channel(cirq.X.with_probability(sympy.Symbol('x')), None) is None
+    assert not cirq.has_kraus(NoDetailsGate().with_probability(0.5))
+    assert cirq.kraus(NoDetailsGate().with_probability(0.5), None) is None
+    assert cirq.kraus(cirq.X.with_probability(sympy.Symbol('x')), None) is None
     assert_channel_sums_to_identity(cirq.X.with_probability(0.25))
     assert_channel_sums_to_identity(cirq.bit_flip(0.75).with_probability(0.25))
     assert_channel_sums_to_identity(cirq.amplitude_damp(0.75).with_probability(0.25))
 
-    m = cirq.channel(cirq.X.with_probability(0.25))
+    m = cirq.kraus(cirq.X.with_probability(0.25))
     assert len(m) == 2
     np.testing.assert_allclose(
         m[0],
@@ -188,7 +188,7 @@ def num_qubits(self) -> int:
         atol=1e-8,
     )
 
-    m = cirq.channel(cirq.bit_flip(0.75).with_probability(0.25))
+    m = cirq.kraus(cirq.bit_flip(0.75).with_probability(0.25))
     assert len(m) == 3
     np.testing.assert_allclose(
         m[0],
@@ -206,7 +206,7 @@ def num_qubits(self) -> int:
         atol=1e-8,
     )
 
-    m = cirq.channel(cirq.amplitude_damp(0.75).with_probability(0.25))
+    m = cirq.kraus(cirq.amplitude_damp(0.75).with_probability(0.25))
     assert len(m) == 3
     np.testing.assert_allclose(
         m[0],

cirq-core/cirq/ops/raw_types.py

@@ -656,10 +656,10 @@ def _mixture_(self) -> Sequence[Tuple[float, Any]]:
         return protocols.mixture(self.sub_operation, NotImplemented)
 
     def _has_kraus_(self) -> bool:
-        return protocols.has_channel(self.sub_operation)
+        return protocols.has_kraus(self.sub_operation)
 
     def _kraus_(self) -> Union[Tuple[np.ndarray], NotImplementedType]:
-        return protocols.channel(self.sub_operation, NotImplemented)
+        return protocols.kraus(self.sub_operation, NotImplemented)
 
     def _measurement_key_(self) -> str:
         return protocols.measurement_key(self.sub_operation, NotImplemented)

cirq-core/cirq/ops/raw_types_test.py

@@ -589,7 +589,7 @@ def test_tagged_operation_forwards_protocols():
     assert cirq.decompose(tagged_h) == cirq.decompose(h)
     assert cirq.pauli_expansion(tagged_h) == cirq.pauli_expansion(h)
     assert cirq.equal_up_to_global_phase(h, tagged_h)
-    assert np.isclose(cirq.channel(h), cirq.channel(tagged_h)).all()
+    assert np.isclose(cirq.kraus(h), cirq.kraus(tagged_h)).all()
 
     assert cirq.measurement_key(cirq.measure(q1, key='blah').with_tags(tag)) == 'blah'
 
@@ -631,7 +631,7 @@ def test_tagged_operation_forwards_protocols():
     flip = cirq.bit_flip(0.5)(q1)
     tagged_flip = cirq.bit_flip(0.5)(q1).with_tags(tag)
     assert cirq.has_mixture(tagged_flip)
-    assert cirq.has_channel(tagged_flip)
+    assert cirq.has_kraus(tagged_flip)
 
     flip_mixture = cirq.mixture(flip)
     tagged_mixture = cirq.mixture(tagged_flip)

cirq-core/cirq/protocols/__init__.py

@@ -40,8 +40,11 @@
 )
 from cirq.protocols.channel import (
     channel,
+    kraus,
     has_channel,
+    has_kraus,
     SupportsChannel,
+    SupportsKraus,
 )
 from cirq.protocols.commutes_protocol import (
     commutes,

cirq-core/cirq/protocols/apply_channel_protocol.py

@@ -24,7 +24,7 @@
     apply_unitary,
     ApplyUnitaryArgs,
 )
-from cirq.protocols.channel import channel
+from cirq.protocols.channel import kraus
 from cirq.protocols import qid_shape_protocol
 from cirq.type_workarounds import NotImplementedType
 
@@ -257,9 +257,9 @@ def err_str(buf_num_str):
         return result
 
     # Fallback to using the object's `_kraus_` matrices.
-    kraus = channel(val, None)
-    if kraus is not None:
-        return _apply_kraus(kraus, args)
+    ks = kraus(val, None)
+    if ks is not None:
+        return _apply_kraus(ks, args)
 
     # Don't know how to apply channel. Fallback to specified default behavior.
     if default is not RaiseTypeErrorIfNotProvided: