enable inverse of classically conditioned gate

qiskit/circuit/controlledgate.py

@@ -13,7 +13,7 @@
 """Controlled unitary gate."""
 
 import copy
-from typing import List, Optional, Union
+from typing import List, Optional, Union, Tuple, TYPE_CHECKING
 
 from qiskit.circuit.exceptions import CircuitError
 
@@ -23,6 +23,9 @@
 from .quantumregister import QuantumRegister
 from ._utils import _ctrl_state_to_int
 
+# pylint: disable=cyclic-import
+from .classicalregister import ClassicalRegister, Clbit
+
 
 class ControlledGate(Gate):
     """Controlled unitary gate."""
@@ -37,6 +40,7 @@ def __init__(
         definition: Optional["QuantumCircuit"] = None,
         ctrl_state: Optional[Union[int, str]] = None,
         base_gate: Optional[Gate] = None,
+        condition: Optional[Tuple[Union["ClassicalRegister", "Clbit"], int]] = None,
     ):
         """Create a new ControlledGate. In the new gate the first ``num_ctrl_qubits``
         of the gate are the controls.
@@ -55,6 +59,8 @@ def __init__(
                 must equal num_ctrl_qubits, MSB on left. If None, use
                 2**num_ctrl_qubits-1.
             base_gate: Gate object to be controlled.
+            condition (tuple[ClassicalRegister or Clbit, int] or None: classical
+                condition of instruction.
 
         Raises:
             CircuitError: If ``num_ctrl_qubits`` >= ``num_qubits``.

qiskit/circuit/gate.py

@@ -26,7 +26,12 @@ class Gate(Instruction):
     """Unitary gate."""
 
     def __init__(
-        self, name: str, num_qubits: int, params: List, label: Optional[str] = None
+        self,
+        name: str,
+        num_qubits: int,
+        params: List,
+        label: Optional[str] = None,
+        condition: Optional[Tuple] = None,
     ) -> None:
         """Create a new gate.
 
@@ -35,9 +40,11 @@ def __init__(
             num_qubits: The number of qubits the gate acts on.
             params: A list of parameters.
             label: An optional label for the gate.
+            condition (tuple[ClassicalRegister or Clbit, int] or None: classical
+                condition of instruction.
         """
         self.definition = None
-        super().__init__(name, num_qubits, 0, params, label=label)
+        super().__init__(name, num_qubits, 0, params, label=label, condition=condition)
 
     # Set higher priority than Numpy array and matrix classes
     __array_priority__ = 20

qiskit/circuit/instruction.py

@@ -53,7 +53,17 @@ class Instruction:
     # NOTE: Using this attribute may change in the future (See issue # 5811)
     _directive = False
 
-    def __init__(self, name, num_qubits, num_clbits, params, duration=None, unit="dt", label=None):
+    def __init__(
+        self,
+        name,
+        num_qubits,
+        num_clbits,
+        params,
+        duration=None,
+        unit="dt",
+        label=None,
+        condition=None,
+    ):
         """Create a new instruction.
 
         Args:
@@ -65,6 +75,8 @@ def __init__(self, name, num_qubits, num_clbits, params, duration=None, unit="dt
             duration (int or float): instruction's duration. it must be integer if ``unit`` is 'dt'
             unit (str): time unit of duration
             label (str or None): An optional label for identifying the instruction.
+            condition (tuple[ClassicalRegister or Clbit, int] or None: classical
+                condition of instruction.
 
         Raises:
             CircuitError: when the register is not in the correct format.
@@ -88,7 +100,8 @@ def __init__(self, name, num_qubits, num_clbits, params, duration=None, unit="dt
             self._label = label
         # tuple (ClassicalRegister, int), tuple (Clbit, bool) or tuple (Clbit, int)
         # when the instruction has a conditional ("if")
-        self.condition = None
+        self._cl_condition = None  # note: "_condition" was taken by the "assemble" method
+        self.condition = condition
         # list of instructions (and their contexts) that this instruction is composed of
         # empty definition means opaque or fundamental instruction
         self._definition = None
@@ -108,13 +121,15 @@ def __eq__(self, other):
         Returns:
             bool: are self and other equal.
         """
-        if (
+        neq_cond = bool(
             type(self) is not type(other)
             or self.name != other.name
             or self.num_qubits != other.num_qubits
             or self.num_clbits != other.num_clbits
             or self.definition != other.definition
-        ):
+            or self.condition != other.condition
+        )
+        if neq_cond:
             return False
 
         for self_param, other_param in zip_longest(self.params, other.params):
@@ -311,6 +326,41 @@ def label(self, name: str):
         else:
             raise TypeError("label expects a string or None")
 
+    @property
+    def condition(self) -> tuple:
+        """Get the classical condition of the instruction.
+
+        Returns:
+            tuple(ClassicalRegister or Clbit, int) or None: classical condition.
+        """
+        return self._cl_condition
+
+    @condition.setter
+    def condition(self, setting):
+        """Set classical condition of instruction.
+
+        Args:
+            setting (tuple(ClassicalRegister or Clbit, int)): where the first
+                element are the bits and the second is the value.
+        Raises:
+            CircuitError: type/value errors.
+        """
+        if setting is None:
+            return
+        classical, value = setting
+        if not isinstance(classical, (ClassicalRegister, Clbit)):
+            breakpoint()
+            raise CircuitError(
+                "condition must be used with a classical register or " "classical bit"
+            )
+        if value < 0:
+            raise CircuitError("condition valueue should be non-negative")
+        if isinstance(classical, Clbit):
+            # Casting the conditional valueue as Boolean when
+            # the classical condition is on a classical bit.
+            value = bool(value)
+        self._cl_condition = (classical, value)
+
     def mirror(self):
         """DEPRECATED: use instruction.reverse_ops().
 
@@ -376,6 +426,7 @@ def inverse(self):
                 num_qubits=self.num_qubits,
                 num_clbits=self.num_clbits,
                 params=self.params.copy(),
+                condition=self.condition,
             )
 
         else:
@@ -394,14 +445,6 @@ def inverse(self):
 
     def c_if(self, classical, val):
         """Add classical condition on register or cbit classical and value val."""
-        if not isinstance(classical, (ClassicalRegister, Clbit)):
-            raise CircuitError("c_if must be used with a classical register or classical bit")
-        if val < 0:
-            raise CircuitError("condition value should be non-negative")
-        if isinstance(classical, Clbit):
-            # Casting the conditional value as Boolean when
-            # the classical condition is on a classical bit.
-            val = bool(val)
         self.condition = (classical, val)
         return self
 

qiskit/circuit/library/generalized_gates/gms.py

@@ -107,9 +107,9 @@ class MSGate(Gate):
     and is thus reduced to the RXXGate.
     """
 
-    def __init__(self, num_qubits, theta, label=None):
+    def __init__(self, num_qubits, theta, label=None, condition=None):
         """Create new MS gate."""
-        super().__init__("ms", num_qubits, [theta], label=label)
+        super().__init__("ms", num_qubits, [theta], label=label, condition=condition)
 
     def _define(self):
         theta = self.params[0]

qiskit/circuit/library/generalized_gates/pauli.py

@@ -35,8 +35,8 @@ class PauliGate(Gate):
     the pauli gates sequentially using standard Qiskit gates
     """
 
-    def __init__(self, label):
-        super().__init__("pauli", len(label), [label])
+    def __init__(self, label, condition=None):
+        super().__init__("pauli", len(label), [label], condition=condition)
 
     def _define(self):
         """
@@ -55,7 +55,7 @@ def _define(self):
 
     def inverse(self):
         r"""Return inverted pauli gate (itself)."""
-        return PauliGate(self.params[0])  # self-inverse
+        return PauliGate(self.params[0], condition=self.condition)  # self-inverse
 
     def __array__(self, dtype=None):
         """Return a Numpy.array for the pauli gate.

qiskit/circuit/library/generalized_gates/rv.py

@@ -42,7 +42,7 @@ class RVGate(Gate):
                 \end{pmatrix}
     """
 
-    def __init__(self, v_x, v_y, v_z, basis="U"):
+    def __init__(self, v_x, v_y, v_z, basis="U", condition=None):
         """Create new rv single-qubit gate.
 
         Args:
@@ -55,7 +55,7 @@ def __init__(self, v_x, v_y, v_z, basis="U"):
         # pylint: disable=cyclic-import
         from qiskit.quantum_info.synthesis.one_qubit_decompose import OneQubitEulerDecomposer
 
-        super().__init__("rv", 1, [v_x, v_y, v_z])
+        super().__init__("rv", 1, [v_x, v_y, v_z], condition=condition)
         self._decomposer = OneQubitEulerDecomposer(basis=basis)
 
     def _define(self):
@@ -69,7 +69,7 @@ def _define(self):
     def inverse(self):
         """Invert this gate."""
         vx, vy, vz = self.params
-        return RVGate(-vx, -vy, -vz)
+        return RVGate(-vx, -vy, -vz, condition=self.condition)
 
     def to_matrix(self):
         """Return a numpy.array for the R(v) gate."""

qiskit/circuit/library/standard_gates/dcx.py

@@ -44,9 +44,9 @@ class DCXGate(Gate):
             \end{pmatrix}
     """
 
-    def __init__(self):
+    def __init__(self, condition=None):
         """Create new DCX gate."""
-        super().__init__("dcx", 2, [])
+        super().__init__("dcx", 2, [], condition=condition)
 
     def _define(self):
         """

qiskit/circuit/library/standard_gates/ecr.py

@@ -76,9 +76,9 @@ class ECRGate(Gate):
                 \end{pmatrix}
     """
 
-    def __init__(self):
+    def __init__(self, condition=None):
         """Create new ECR gate."""
-        super().__init__("ecr", 2, [])
+        super().__init__("ecr", 2, [], condition=condition)
 
     def _define(self):
         """

qiskit/circuit/library/standard_gates/h.py

@@ -47,9 +47,9 @@ class HGate(Gate):
             \end{pmatrix}
     """
 
-    def __init__(self, label=None):
+    def __init__(self, label=None, condition=None):
         """Create new H gate."""
-        super().__init__("h", 1, [], label=label)
+        super().__init__("h", 1, [], label=label, condition=condition)
 
     def _define(self):
         """
@@ -89,7 +89,7 @@ def control(self, num_ctrl_qubits=1, label=None, ctrl_state=None):
 
     def inverse(self):
         r"""Return inverted H gate (itself)."""
-        return HGate()  # self-inverse
+        return HGate(condition=self.condition)  # self-inverse
 
     def __array__(self, dtype=None):
         """Return a Numpy.array for the H gate."""
@@ -158,10 +158,17 @@ class CHGate(ControlledGate):
         dtype=complex,
     )
 
-    def __init__(self, label=None, ctrl_state=None):
+    def __init__(self, label=None, ctrl_state=None, condition=None):
         """Create new CH gate."""
         super().__init__(
-            "ch", 2, [], num_ctrl_qubits=1, label=label, ctrl_state=ctrl_state, base_gate=HGate()
+            "ch",
+            2,
+            [],
+            num_ctrl_qubits=1,
+            label=label,
+            ctrl_state=ctrl_state,
+            base_gate=HGate(),
+            condition=condition,
         )
 
     def _define(self):
@@ -198,7 +205,7 @@ def _define(self):
 
     def inverse(self):
         """Return inverted CH gate (itself)."""
-        return CHGate(ctrl_state=self.ctrl_state)  # self-inverse
+        return CHGate(ctrl_state=self.ctrl_state, condition=self.condition)  # self-inverse
 
     def __array__(self, dtype=None):
         """Return a numpy.array for the CH gate."""

qiskit/circuit/library/standard_gates/i.py

@@ -39,13 +39,13 @@ class IGate(Gate):
              └───┘
     """
 
-    def __init__(self, label=None):
+    def __init__(self, label=None, condition=None):
         """Create new Identity gate."""
-        super().__init__("id", 1, [], label=label)
+        super().__init__("id", 1, [], label=label, condition=condition)
 
     def inverse(self):
         """Invert this gate."""
-        return IGate()  # self-inverse
+        return IGate(condition=self.condition)  # self-inverse
 
     def __array__(self, dtype=None):
         """Return a numpy.array for the identity gate."""

qiskit/circuit/library/standard_gates/ms.py

@@ -30,7 +30,7 @@ class MSGate(Gate):
     and is thus reduced to the RXXGate.
     """
 
-    def __init__(self, num_qubits, theta, label=None):
+    def __init__(self, num_qubits, theta, label=None, condition=None):
         """Create new MS gate."""
         warnings.warn(
             "The qiskit.circuit.library.standard_gates.ms import "
@@ -40,7 +40,7 @@ def __init__(self, num_qubits, theta, label=None):
             DeprecationWarning,
             stacklevel=2,
         )
-        super().__init__("ms", num_qubits, [theta], label=label)
+        super().__init__("ms", num_qubits, [theta], label=label, condition=condition)
 
     def _define(self):
         # pylint: disable=cyclic-import