Add support for negative control for OpenQASMBackend

Author: Takishima

projectq/backends/_qasm.py

@@ -17,7 +17,7 @@
 from copy import deepcopy
 
 from projectq.cengines import BasicEngine
-from projectq.meta import get_control_count
+from projectq.meta import get_control_count, has_negative_control
 from projectq.ops import (
     X,
     NOT,
@@ -41,6 +41,7 @@
     FlushGate,
 )
 
+
 # ==============================================================================
 
 
@@ -115,9 +116,11 @@ def is_available(self, cmd):
         Args:
             cmd (Command): Command for which to check availability
         """
-        gate = cmd.gate
-        n_controls = get_control_count(cmd)
+        if has_negative_control(cmd):
+            return False
 
+        n_controls = get_control_count(cmd)
+        gate = cmd.gate
         is_available = False
 
         if gate in (Measure, Allocate, Deallocate, Barrier):

projectq/backends/_qasm_test.py

@@ -42,6 +42,7 @@
     Command,
     All,
 )
+from projectq.types import WeakQubitRef
 from ._qasm import OpenQASMBackend
 
 # ==============================================================================
@@ -206,6 +207,22 @@ def test_qasm_is_available_2control(gate, is_available):
     assert eng.is_available(cmd) == is_available
 
 
+def test_ibm_backend_is_available_negative_control():
+    backend = OpenQASMBackend()
+    backend.is_last_engine = True
+
+    qb0 = WeakQubitRef(engine=None, idx=0)
+    qb1 = WeakQubitRef(engine=None, idx=1)
+
+    assert backend.is_available(Command(None, X, qubits=([qb0],), controls=[qb1]))
+    assert backend.is_available(Command(None, X, qubits=([qb0],), controls=[qb1], control_state='1'))
+    assert not backend.is_available(Command(None, X, qubits=([qb0],), controls=[qb1], control_state='0'))
+
+    assert backend.is_available(Command(None, X, qubits=([qb0],), controls=[qb1]))
+    assert backend.is_available(Command(None, X, qubits=([qb0],), controls=[qb1], control_state='1'))
+    assert not backend.is_available(Command(None, X, qubits=([qb0],), controls=[qb1], control_state='0'))
+
+
 def test_qasm_test_qasm_single_qubit_gates():
     eng = MainEngine(backend=OpenQASMBackend(), engine_list=[])
     qubit = eng.allocate_qubit()