Updated Molmer Sorensen to do Rxx and Ryy

Added phase term to allow for MS gate
qutip · Mar 9, 2023 · 0b53044 · 0b53044
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Showing 3 changed files with 24 additions and 11 deletions.
diff --git a/src/qutip_qip/operations/gateclass.py b/src/qutip_qip/operations/gateclass.py
@@ -872,16 +872,16 @@ class MS(TwoQubitGate):
     .. math::
 
         \begin{pmatrix}
-        \cos(\frac{\theta}{2}) & 0 & 0 & -i\sin(\frac{\theta}{2}) \\
+        \cos(\frac{\theta}{2}) & 0 & 0 & -i\exp^{-i2\phi}\sin(\frac{\theta}{2}) \\
         0 & \cos(\frac{\theta}{2}) & -i\sin(\frac{\theta}{2}) & 0 \\
         0 & -i\sin(\frac{\theta}{2}) & \cos(\frac{\theta}{2}) & 0 \\
-        -i\sin(\frac{\theta}{2}) & 0 & 0 & \cos(\frac{\theta}{2})
+        -i\exp^{i2\phi}\sin(\frac{\theta}{2}) & 0 & 0 & \cos(\frac{\theta}{2})
         \end{pmatrix}
 
     Examples
     --------
     >>> from qutip_qip.operations import MS
-    >>> MS([0, 1], np.pi/2).get_compact_qobj() # doctest: +NORMALIZE_WHITESPACE
+    >>> MS([0, 1], (np.pi/2, 0)).get_compact_qobj() # doctest: +NORMALIZE_WHITESPACE
     Quantum object: dims = [[2, 2], [2, 2]], shape = (4, 4), type = oper, isherm = False
     Qobj data =
     [[0.70711+0.j      0.     +0.j      0.     +0.j      0.     -0.70711j]

diff --git a/src/qutip_qip/operations/gates.py b/src/qutip_qip/operations/gates.py
@@ -775,14 +775,16 @@ def sqrtiswap(N=None, targets=[0, 1]):
     )
 
 
-def molmer_sorensen(theta, N=None, targets=[0, 1]):
+def molmer_sorensen(theta, phi=0.0, N=None, targets=[0, 1]):
     """
     Quantum object of a Mølmer–Sørensen gate.
 
     Parameters
     ----------
     theta: float
         The duration of the interaction pulse.
+    phi: float
+        Rotation axis. phi = 0 for XX; phi=pi for YY
     N: int
         Number of qubits in the system.
     target: int
@@ -801,12 +803,23 @@ def molmer_sorensen(theta, N=None, targets=[0, 1]):
         return expand_operator(
             molmer_sorensen(theta), dims=[2] * N, targets=targets
         )
+
     return Qobj(
-        [
-            [np.cos(theta / 2.0), 0, 0, -1.0j * np.sin(theta / 2.0)],
-            [0, np.cos(theta / 2.0), -1.0j * np.sin(theta / 2.0), 0],
-            [0, -1.0j * np.sin(theta / 2.0), np.cos(theta / 2.0), 0],
-            [-1.0j * np.sin(theta / 2.0), 0, 0, np.cos(theta / 2.0)],
+        [   
+            [
+                np.cos(theta / 2),
+                0,
+                0,
+                -1j * np.exp(-1j * 2 * phi) * np.sin(theta / 2),
+            ],
+            [0, np.cos(theta / 2), -1j * np.sin(theta / 2), 0],
+            [0, -1j * np.sin(theta / 2), np.cos(theta / 2), 0],
+            [
+                -1j * np.exp(1j * 2 * phi) * np.sin(theta / 2),
+                0,
+                0,
+                np.cos(theta / 2),
+            ],
         ],
         dims=[[2, 2], [2, 2]],
     )

diff --git a/tests/test_gates.py b/tests/test_gates.py
@@ -365,7 +365,7 @@ def test_gates_class():
     circuit1.add_gate("SQRTSWAP", [2, 0])
     circuit1.add_gate("SQRTISWAP", [0, 1])
     circuit1.add_gate("SWAPALPHA", [1, 2], arg_value=np.pi/4)
-    circuit1.add_gate("MS", [1, 0], arg_value=np.pi/4)
+    circuit1.add_gate("MS", [1, 0], arg_value=(np.pi/4, np.pi/7))
     circuit1.add_gate("TOFFOLI", [2, 0, 1])
     circuit1.add_gate("FREDKIN", [0, 1, 2])
     circuit1.add_gate("BERKELEY", [1, 0])
@@ -392,7 +392,7 @@ def test_gates_class():
     circuit2.add_gate(SQRTSWAP([2, 0]))
     circuit2.add_gate(SQRTISWAP([0, 1]))
     circuit2.add_gate(SWAPALPHA([1, 2], np.pi/4))
-    circuit2.add_gate(MS([1, 0], np.pi/4))
+    circuit2.add_gate(MS([1, 0], (np.pi/4, np.pi/7)))
     circuit2.add_gate(TOFFOLI([2, 0, 1]))
     circuit2.add_gate(FREDKIN([0, 1, 2]))
     circuit2.add_gate(BERKELEY([1, 0]))