diff --git a/qiskit/mapper/_mapping.py b/qiskit/mapper/_mapping.py
index 5cbd2b4a02f1..3f5d91130410 100644
--- a/qiskit/mapper/_mapping.py
+++ b/qiskit/mapper/_mapping.py
@@ -25,7 +25,7 @@
 from qiskit.dagcircuit._dagcircuiterror import DAGCircuitError
 from qiskit.unrollers._dagunroller import DagUnroller
 from qiskit.unrollers._dagbackend import DAGBackend
-from qiskit.mapper._quaternion import quaternion_from_euler
+from qiskit.quantum_info.operators.quaternion import quaternion_from_euler
 from qiskit import QuantumRegister
 
 logger = logging.getLogger(__name__)
diff --git a/qiskit/mapper/_quaternion.py b/qiskit/quantum_info/operators/quaternion.py
similarity index 81%
rename from qiskit/mapper/_quaternion.py
rename to qiskit/quantum_info/operators/quaternion.py
index 0c77b5fb8b25..92a9533f4ee2 100644
--- a/qiskit/mapper/_quaternion.py
+++ b/qiskit/quantum_info/operators/quaternion.py
@@ -144,39 +144,3 @@ def quaternion_from_euler(angles, order='yzy'):
            * quaternion_from_axis_rotation(angles[2], order[2]))
     quat.normalize(inplace=True)
     return quat
-
-
-def _rotm(angle, axis):
-    """Generates a rotation matrix for a given angle and axis.
-
-    Args:
-        angle (float): Rotation angle in radians.
-        axis (str): Axis for rotation: 'x', 'y', 'z'
-
-    Returns:
-        ndarray: Rotation matrix.
-
-    Raises:
-        ValueError: Invalid input axis.
-    """
-    direction = np.zeros(3, dtype=float)
-    if axis == 'x':
-        direction[0] = 1
-    elif axis == 'y':
-        direction[1] = 1
-    elif axis == 'z':
-        direction[2] = 1
-    else:
-        raise ValueError('Invalid axis.')
-    direction = np.asarray(direction, dtype=float)
-    sin_angle = math.sin(angle)
-    cos_angle = math.cos(angle)
-    rot = np.diag([cos_angle, cos_angle, cos_angle])
-    rot += np.outer(direction, direction) * (1.0 - cos_angle)
-    direction *= sin_angle
-    rot += np.array([
-        [0, -direction[2], direction[1]],
-        [direction[2], 0, -direction[0]],
-        [-direction[1], direction[0], 0]
-    ])
-    return rot
diff --git a/qiskit/quantum_info/operators/unitary.py b/qiskit/quantum_info/operators/unitary.py
new file mode 100644
index 000000000000..4732ea22d5f5
--- /dev/null
+++ b/qiskit/quantum_info/operators/unitary.py
@@ -0,0 +1,48 @@
+# -*- coding: utf-8 -*-
+
+# Copyright 2018, IBM.
+#
+# This source code is licensed under the Apache License, Version 2.0 found in
+# the LICENSE.txt file in the root directory of this source tree.
+
+"""
+A module for common unitary matrix.
+"""
+import math
+import numpy as np
+
+
+def rotation_matrix(angle, axis):
+    """Generates a rotation matrix for a given angle and axis.
+
+    Args:
+        angle (float): Rotation angle in radians.
+        axis (str): Axis for rotation: 'x', 'y', 'z'
+
+    Returns:
+        ndarray: Rotation matrix.
+
+    Raises:
+        ValueError: Invalid input axis.
+    """
+    direction = np.zeros(3, dtype=float)
+    if axis == 'x':
+        direction[0] = 1
+    elif axis == 'y':
+        direction[1] = 1
+    elif axis == 'z':
+        direction[2] = 1
+    else:
+        raise ValueError('Invalid axis.')
+    direction = np.asarray(direction, dtype=float)
+    sin_angle = math.sin(angle)
+    cos_angle = math.cos(angle)
+    rot = np.diag([cos_angle, cos_angle, cos_angle])
+    rot += np.outer(direction, direction) * (1.0 - cos_angle)
+    direction *= sin_angle
+    rot += np.array([
+        [0, -direction[2], direction[1]],
+        [direction[2], 0, -direction[0]],
+        [-direction[1], direction[0], 0]
+    ])
+    return rot
diff --git a/test/python/test_quaternions.py b/test/python/quantum_info/test_quaternions.py
similarity index 88%
rename from test/python/test_quaternions.py
rename to test/python/quantum_info/test_quaternions.py
index b0211201cf54..8bb1f81dad44 100644
--- a/test/python/test_quaternions.py
+++ b/test/python/quantum_info/test_quaternions.py
@@ -8,8 +8,9 @@
 """Tests qiskit/mapper/_quaternion"""
 import numpy as np
 import scipy.linalg as la
-from qiskit.mapper._quaternion import (quaternion_from_euler, _rotm)
-from .common import QiskitTestCase
+from qiskit.quantum_info.operators.quaternion import quaternion_from_euler
+from qiskit.quantum_info.operators.unitary import rotation_matrix
+from ..common import QiskitTestCase
 
 
 class TestQuaternions(QiskitTestCase):
@@ -22,8 +23,9 @@ def test_random_euler(self):
         for _ in range(1000):
             rnd = 4*np.pi*(np.random.random(3)-0.5)
             idx = np.random.randint(3, size=3)
-            mat1 = _rotm(rnd[0], axes[idx[0]]).dot(
-                _rotm(rnd[1], axes[idx[1]]).dot(_rotm(rnd[2], axes[idx[2]])))
+            mat1 = rotation_matrix(rnd[0], axes[idx[0]]).dot(
+                rotation_matrix(rnd[1], axes[idx[1]]).dot(
+                    rotation_matrix(rnd[2], axes[idx[2]])))
             axes_str = ''.join(axes[i] for i in idx)
             quat = quaternion_from_euler(rnd, axes_str)
             mat2 = quat.to_matrix()