Allow computing cost from decomposition of cirq gates (#1510)

Author: anurudhp

qualtran/bloqs/basic_gates/rotation.py

@@ -108,7 +108,7 @@ def _z_pow() -> ZPowGate:
 
 @frozen
 class CZPowGate(CirqGateAsBloqBase):
-    exponent: float = 1.0
+    exponent: SymbolicFloat = 1.0
     global_shift: float = 0.0
     eps: SymbolicFloat = 1e-11
 

qualtran/cirq_interop/_cirq_to_bloq.py

@@ -150,9 +150,11 @@ def cirq_gate(self) -> cirq.Gate:
     def my_static_costs(self, cost_key: 'CostKey'):
         if isinstance(cost_key, QECGatesCost):
             t_count = _from_directly_countable_cirq(self.cirq_gate)
-            if t_count is None:
-                raise ValueError(f"Cirq gate must be directly countable, not {self.cirq_gate}")
-            return GateCounts(t=t_count.t, rotation=t_count.rotations, clifford=t_count.clifford)
+            if t_count is not None:
+                return GateCounts(
+                    t=t_count.t, rotation=t_count.rotations, clifford=t_count.clifford
+                )
+        return NotImplemented
 
 
 def _cirq_wire_symbol_to_qualtran_wire_symbol(symbol: str, side: Side) -> 'WireSymbol':

qualtran/cirq_interop/_cirq_to_bloq_test.py

@@ -17,6 +17,7 @@
 import cirq
 import numpy as np
 import pytest
+import sympy
 from attrs import frozen
 
 import qualtran
@@ -34,11 +35,12 @@
     SoquetT,
 )
 from qualtran._infra.gate_with_registers import get_named_qubits
-from qualtran.bloqs.basic_gates import CNOT, GlobalPhase, OneState
+from qualtran.bloqs.basic_gates import CNOT, CZPowGate, GlobalPhase, OneState, YPowGate
 from qualtran.bloqs.bookkeeping import Allocate, Free, Join, Split
 from qualtran.bloqs.mcmt.and_bloq import And
 from qualtran.cirq_interop import cirq_optree_to_cbloq, CirqGateAsBloq, CirqQuregT
 from qualtran.cirq_interop.t_complexity_protocol import TComplexity
+from qualtran.resource_counting import GateCounts, get_cost_value, QECGatesCost
 
 
 @frozen
@@ -228,3 +230,16 @@ def test_cirq_gate_as_bloq_decompose_raises():
 
 def test_cirq_gate_as_bloq_diagram_info():
     assert cirq.circuit_diagram_info(GlobalPhase(exponent=0.5)) is None
+
+
+def test_cirq_gate_cost_via_decomp():
+    theta = sympy.Symbol("theta", real=True)
+    cirq_swappow = cirq.SwapPowGate(exponent=theta)
+
+    swappow_bloq = CirqGateAsBloq(cirq_swappow)
+
+    _, sigma = swappow_bloq.call_graph()
+    assert sigma == {CNOT(): 2, YPowGate(0.5): 1, YPowGate(-0.5): 1, CZPowGate(theta): 1}
+
+    gc_swappow = get_cost_value(swappow_bloq, QECGatesCost())
+    assert gc_swappow == GateCounts(clifford=4, rotation=1)