Fixing MS gate inverse is not implemented correctly (Issue 7432) (#7466)

Fixing MS gate inverse is not implemented correctly (Issue
#7432)

The MS gate has a theta entanglement angle parameter in it's signature,
with a 0.25 default value. The problems that need to be corrected here
is that when implementing the inverse MS gate the theta parameter is not
applied, and instead implicitly its default value is being used when
specifying inverse of MS in terms of MS.

Code and tests were updated.

---------

Co-authored-by: Michael Hucka <mhucka@caltech.edu>

Author: radumarg

cirq-ionq/cirq_ionq/ionq_native_gates.py

@@ -248,7 +248,7 @@ def __pow__(self, power):
             return self
 
         if power == -1:
-            return MSGate(phi0=self.phi0 + 0.5, phi1=self.phi1)
+            return MSGate(phi0=self.phi0 + 0.5, phi1=self.phi1, theta=self.theta)
 
         return NotImplemented
 

cirq-ionq/cirq_ionq/ionq_native_gates_test.py

@@ -100,7 +100,10 @@ def test_zz_unitary(phase):
     [
         *[ionq.GPIGate(phi=angle) for angle in PARAMS_FOR_ONE_ANGLE_GATE],
         *[ionq.GPI2Gate(phi=angle) for angle in PARAMS_FOR_ONE_ANGLE_GATE],
-        *[ionq.MSGate(phi0=angles[0], phi1=angles[1]) for angles in PARAMS_FOR_TWO_ANGLE_GATE],
+        *[
+            ionq.MSGate(phi0=angles[0], phi1=angles[1], theta=0.8)
+            for angles in PARAMS_FOR_TWO_ANGLE_GATE
+        ],
         *[ionq.ZZGate(theta=angle) for angle in PARAMS_FOR_ONE_ANGLE_GATE],
     ],
 )