Add decomposition for CCZ gate and IonQTargetGateset when qubits are …

…all-to-all connected (#6095)

cirq-ionq/cirq_ionq/__init__.py

@@ -18,7 +18,7 @@
 
 from cirq_ionq.ionq_devices import IonQAPIDevice, decompose_to_device
 
-from cirq_ionq.ionq_gateset import IonQTargetGateset
+from cirq_ionq.ionq_gateset import IonQTargetGateset, decompose_all_to_all_connect_ccz_gate
 
 from cirq_ionq.ionq_exceptions import (
     IonQException,

cirq-ionq/cirq_ionq/ionq_gateset.py

@@ -16,6 +16,7 @@
 from typing import Any
 from typing import Dict
 from typing import List
+from typing import Tuple
 
 import cirq
 
@@ -78,12 +79,21 @@ def _decompose_two_qubit_operation(self, op: cirq.Operation, _) -> cirq.OP_TREE:
             temp, k=1, rewriter=lambda op: self._decompose_single_qubit_operation(op, -1)
         ).all_operations()
 
+    def _decompose_multi_qubit_operation(self, op: cirq.Operation, _) -> cirq.OP_TREE:
+        if isinstance(op.gate, cirq.CCZPowGate):
+            return decompose_all_to_all_connect_ccz_gate(op.gate, op.qubits)
+        return NotImplemented
+
     @property
     def preprocess_transformers(self) -> List['cirq.TRANSFORMER']:
-        """List of transformers which should be run before decomposing individual operations."""
+        """List of transformers which should be run before decomposing individual operations.
+
+        Decompose to three qubit gates because three qubit gates have different decomposition
+        for all-to-all connectivity between qubits.
+        """
         return [
             cirq.create_transformer_with_kwargs(
-                cirq.expand_composite, no_decomp=lambda op: cirq.num_qubits(op) <= self.num_qubits
+                cirq.expand_composite, no_decomp=lambda op: cirq.num_qubits(op) <= 3
             )
         ]
 
@@ -104,3 +114,53 @@ def _json_dict_(self) -> Dict[str, Any]:
     @classmethod
     def _from_json_dict_(cls, atol, **kwargs):
         return cls(atol=atol)
+
+
+def decompose_all_to_all_connect_ccz_gate(
+    ccz_gate: 'cirq.CCZPowGate', qubits: Tuple['cirq.Qid', ...]
+) -> 'cirq.OP_TREE':
+    """Decomposition of all-to-all connected qubits are different from line qubits or grid qubits.
+
+    For example, for qubits in the same ion trap, the decomposition of CCZ gate will be:
+
+    0: ──────────────@──────────────────@───@───p──────@───
+                     │                  │   │          │
+    1: ───@──────────┼───────@───p──────┼───X───p^-1───X───
+          │          │       │          │
+    2: ───X───p^-1───X───p───X───p^-1───X───p──────────────
+
+    where p = T**ccz_gate._exponent
+    """
+    if len(qubits) != 3:
+        raise ValueError(f'Expect 3 qubits for CCZ gate, got {len(qubits)} qubits.')
+
+    a, b, c = qubits
+
+    p = cirq.T**ccz_gate._exponent
+    global_phase = 1j ** (2 * ccz_gate.global_shift * ccz_gate._exponent)
+    global_phase = (
+        complex(global_phase)
+        if cirq.is_parameterized(global_phase) and global_phase.is_complex  # type: ignore
+        else global_phase
+    )
+    global_phase_operation = (
+        [cirq.global_phase_operation(global_phase)]
+        if cirq.is_parameterized(global_phase) or abs(global_phase - 1.0) > 0
+        else []
+    )
+
+    return global_phase_operation + [
+        cirq.CNOT(b, c),
+        p(c) ** -1,
+        cirq.CNOT(a, c),
+        p(c),
+        cirq.CNOT(b, c),
+        p(c) ** -1,
+        cirq.CNOT(a, c),
+        p(b),
+        p(c),
+        cirq.CNOT(a, b),
+        p(a),
+        p(b) ** -1,
+        cirq.CNOT(a, b),
+    ]

cirq-ionq/cirq_ionq/ionq_gateset_test.py

@@ -131,3 +131,46 @@ def test_decompose_parameterized_operation():
             atol=1e-6,
         )
     assert ionq_target_gateset.validate(decomposed_circuit)
+
+
+def test_decomposition_all_to_all_connectivity():
+    """This function only accepts 3 qubits as input"""
+    with pytest.raises(ValueError):
+        decompose_result = ionq.decompose_all_to_all_connect_ccz_gate(
+            cirq.CCZ, cirq.LineQubit.range(4)
+        )
+
+    decompose_result = ionq.decompose_all_to_all_connect_ccz_gate(cirq.CCZ, cirq.LineQubit.range(3))
+
+    cirq.testing.assert_has_diagram(
+        cirq.Circuit(decompose_result),
+        """
+0: ──────────────@──────────────────@───@───T──────@───
+                 │                  │   │          │
+1: ───@──────────┼───────@───T──────┼───X───T^-1───X───
+      │          │       │          │
+2: ───X───T^-1───X───T───X───T^-1───X───T──────────────
+""",
+    )
+
+
+def test_decompose_toffoli_gate():
+    """Decompose result should reflect all-to-all connectivity"""
+    circuit = cirq.Circuit(cirq.TOFFOLI(*cirq.LineQubit.range(3)))
+    decomposed_circuit = cirq.optimize_for_target_gateset(
+        circuit, gateset=ionq_target_gateset, ignore_failures=False
+    )
+    cirq.testing.assert_circuits_with_terminal_measurements_are_equivalent(
+        circuit, decomposed_circuit, atol=1e-8
+    )
+    assert ionq_target_gateset.validate(decomposed_circuit)
+    cirq.testing.assert_has_diagram(
+        decomposed_circuit,
+        """
+0: ──────────────────@──────────────────@───@───T──────@───
+                     │                  │   │          │
+1: ───────@──────────┼───────@───T──────┼───X───T^-1───X───
+          │          │       │          │
+2: ───H───X───T^-1───X───T───X───T^-1───X───T───H──────────
+""",
+    )