add from_matrix

quantumlib · Mar 23, 2024 · e895a93 · e895a93
1 parent f7e47aa
commit e895a93
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diff --git a/qualtran/bloqs/basic_gates/su2_rotation.py b/qualtran/bloqs/basic_gates/su2_rotation.py
@@ -78,6 +78,24 @@ def rotation_matrix(self) -> NDArray[np.complex_]:
             ]
         )
 
+    @staticmethod
+    def from_matrix(mat: NDArray[np.complex_]) -> 'SU2RotationGate':
+        theta = np.arctan2(np.abs(mat[1, 0]), np.abs(mat[0, 0]))
+        if np.isclose(np.cos(theta), 0):
+            alpha = 0
+            phi = np.angle(mat[0, 1] / np.sin(theta))
+            lambd = np.angle(mat[1, 0] / np.sin(theta))
+        else:
+            alpha = np.angle(-mat[1, 1] / np.cos(theta))
+            if np.isclose(np.sin(theta), 0):
+                phi = np.angle(mat[0, 0] / np.cos(theta) * np.exp(-1j * alpha))
+                lambd = 0
+            else:
+                phi = np.angle(mat[0, 1] / np.sin(theta) * np.exp(-1j * alpha))
+                lambd = np.angle(mat[1, 0] / np.sin(theta) * np.exp(-1j * alpha))
+
+        return SU2RotationGate(theta, phi, lambd, alpha)
+
     def add_my_tensors(
         self,
         tn: 'qtn.TensorNetwork',

diff --git a/qualtran/bloqs/basic_gates/su2_rotation_test.py b/qualtran/bloqs/basic_gates/su2_rotation_test.py
@@ -14,7 +14,9 @@
 import cirq
 import numpy as np
 
-from . import Hadamard, TGate
+from qualtran import Bloq
+from qualtran.bloqs.basic_gates import Hadamard, TGate, XGate, YGate, ZGate
+
 from .su2_rotation import _hadamard, _su2_rotation_gate, _t_gate, SU2RotationGate
 
 
@@ -47,3 +49,21 @@ def test_su2_rotation_gates(bloq_autotester):
 def test_su2_rotation_gate_example_unitaries_match():
     np.testing.assert_allclose(_t_gate().tensor_contract(), TGate().tensor_contract())
     np.testing.assert_allclose(_hadamard().tensor_contract(), Hadamard().tensor_contract())
+
+
+def test_from_matrix_on_random_unitaries():
+    random_state = np.random.RandomState(42)
+
+    for _ in range(20):
+        mat = cirq.testing.random_unitary(2, random_state=random_state)
+        np.testing.assert_allclose(SU2RotationGate.from_matrix(mat).rotation_matrix, mat)
+
+
+def test_from_matrix_on_standard_gates():
+    gates: list[Bloq] = [TGate(), XGate(), YGate(), ZGate(), Hadamard()]
+
+    for gate in gates:
+        mat = gate.tensor_contract()
+        np.testing.assert_allclose(
+            SU2RotationGate.from_matrix(mat).rotation_matrix, mat, atol=1e-15
+        )