Add ISWAP_INV constant (#5613)

Fixes #4615

#4624 has not been touched in a long time, so jumping in to fix this.

Author: dabacon

cirq-core/cirq/__init__.py

@@ -241,6 +241,7 @@
     InterchangeableQubitsGate,
     ISWAP,
     ISwapPowGate,
+    ISWAP_INV,
     KrausChannel,
     LinearCombinationOfGates,
     LinearCombinationOfOperations,

cirq-core/cirq/ops/__init__.py

@@ -180,6 +180,7 @@
 from cirq.ops.swap_gates import (
     ISWAP,
     ISwapPowGate,
+    ISWAP_INV,
     riswap,
     SQRT_ISWAP,
     SQRT_ISWAP_INV,

cirq-core/cirq/ops/pauli_string_test.py

@@ -1496,7 +1496,7 @@ def _decompose_(self, qubits):
         cirq.CNOT,
         cirq.CZ,
         cirq.ISWAP,
-        cirq.ISWAP**-1,
+        cirq.ISWAP_INV,
         cirq.SWAP,
         cirq.XX**0.5,
         cirq.YY**0.5,

cirq-core/cirq/ops/swap_gates.py

@@ -16,6 +16,7 @@
 This module creates Gate instances for the following gates:
     SWAP: the swap gate.
     ISWAP: a swap gate with a phase on the swapped subspace.
+    ISWAP_INV: the inverse of the ISWAP gate.
     SQRT_ISWAP: square root of the ISWAP gate.
     SQRT_ISWAP_INV: inverse square root of the ISWAP gate.
 
@@ -284,13 +285,17 @@ def _circuit_diagram_info_(
     def __str__(self) -> str:
         if self._exponent == 1:
             return 'ISWAP'
+        if self._exponent == -1:
+            return 'ISWAP_INV'
         return f'ISWAP**{self._exponent}'
 
     def __repr__(self) -> str:
         e = proper_repr(self._exponent)
         if self._global_shift == 0:
             if self._exponent == 1:
                 return 'cirq.ISWAP'
+            if self._exponent == -1:
+                return 'cirq.ISWAP_INV'
             return f'(cirq.ISWAP**{e})'
         return f'cirq.ISwapPowGate(exponent={e}, global_shift={self._global_shift!r})'
 
@@ -342,6 +347,23 @@ def riswap(rads: value.TParamVal) -> ISwapPowGate:
     """,
 )
 
+ISWAP_INV = ISwapPowGate(exponent=-1)
+document(
+    ISWAP_INV,
+    r"""The inverse of the iswap gate.
+
+    The unitary matrix of this gate is:
+    $$
+    \begin{bmatrix}
+        1 & 0 & 0 & 0 \\
+        0 & 0 & -i & 0 \\
+        0 & -i & 0 & 0 \\
+        0 & 0 & 0 & 1
+    \end{bmatrix}
+    $$
+    """,
+)
+
 SQRT_ISWAP = ISwapPowGate(exponent=0.5)
 document(
     SQRT_ISWAP,

cirq-core/cirq/ops/swap_gates_test.py

@@ -103,6 +103,20 @@ def test_iswap_unitary():
     # yapf: enable
 
 
+def test_iswap_inv_unitary():
+    # yapf: disable
+    cirq.testing.assert_allclose_up_to_global_phase(
+        cirq.unitary(cirq.ISWAP_INV),
+        # Reference for the iswap gate's matrix using +i instead of -i:
+        # https://quantumcomputing.stackexchange.com/questions/2594/
+        np.array([[1, 0, 0, 0],
+                  [0, 0, -1j, 0],
+                  [0, -1j, 0, 0],
+                  [0, 0, 0, 1]]),
+        atol=1e-8)
+    # yapf: enable
+
+
 def test_sqrt_iswap_unitary():
     # yapf: disable
     cirq.testing.assert_allclose_up_to_global_phase(
@@ -138,6 +152,9 @@ def test_repr():
     assert repr(cirq.ISWAP) == 'cirq.ISWAP'
     assert repr(cirq.ISWAP**0.5) == '(cirq.ISWAP**0.5)'
 
+    assert repr(cirq.ISWAP_INV) == 'cirq.ISWAP_INV'
+    assert repr(cirq.ISWAP_INV**0.5) == '(cirq.ISWAP**-0.5)'
+
 
 def test_str():
     assert str(cirq.SWAP) == 'SWAP'
@@ -146,6 +163,9 @@ def test_str():
     assert str(cirq.ISWAP) == 'ISWAP'
     assert str(cirq.ISWAP**0.5) == 'ISWAP**0.5'
 
+    assert str(cirq.ISWAP_INV) == 'ISWAP_INV'
+    assert str(cirq.ISWAP_INV**0.5) == 'ISWAP**-0.5'
+
 
 def test_iswap_decompose_diagram():
     a = cirq.NamedQubit('a')

cirq-core/cirq/protocols/json_test_data/ISWAP_INV.json

@@ -0,0 +1,5 @@
+{
+  "cirq_type": "ISwapPowGate",
+  "exponent": -1,
+  "global_shift": 0.0
+}

cirq-core/cirq/protocols/json_test_data/ISWAP_INV.repr

@@ -0,0 +1 @@
+cirq.ISWAP_INV

cirq-google/cirq_google/serialization/common_serializers.py

@@ -592,7 +592,7 @@ def _add_phase_match(op: cirq.Operation, proto: v2.program_pb2.Operation):
         cirq.SQRT_ISWAP_INV,
         cirq.SQRT_ISWAP,
         cirq.ISWAP,
-        cirq.ISWAP**-1,  # type: ignore
+        cirq.ISWAP_INV,
         SYC,
         cirq.CZ,
     ],
@@ -605,7 +605,7 @@ def _add_phase_match(op: cirq.Operation, proto: v2.program_pb2.Operation):
         cirq.SQRT_ISWAP_INV,
         cirq.SQRT_ISWAP,
         cirq.ISWAP,
-        cirq.ISWAP**-1,  # type: ignore
+        cirq.ISWAP_INV,
     ],
     gate_types_to_check=[cirq.ISwapPowGate],
     allow_symbols=True,

cirq-google/cirq_google/serialization/common_serializers_test.py

@@ -529,6 +529,7 @@ def test_wait_gate_multi_qubit():
         (cirq.ISWAP**1.0, -np.pi / 2, 0),
         (cirq.ISWAP**-1.0, np.pi / 2, 0),
         (cirq.ISWAP**0.0, 0, 0),
+        (cirq.ISWAP_INV, np.pi / 2, 0),
         (cirq.CZ, 0, np.pi),
         (cirq.CZ**-1.0, 0, np.pi),
         (cirq.FSimGate(theta=0, phi=0), 0, 0),