code: def trace_distance(qnode0, qnode1, wires0, wires1):
      r"""
      Compute the trace distance for two :class:`.QNode` returning a :func:`~pennylane.state` (a state can be a state vector
      or a density matrix, depending on the device) acting on quantum systems with the same size.
  
      .. math::
          T(\rho, \sigma)=\frac12\|\rho-\sigma\|_1
          =\frac12\text{Tr}\left(\sqrt{(\rho-\sigma)^{\dagger}(\rho-\sigma)}\right)
  
      where :math:`\|\cdot\|_1` is the Schatten :math:`1`-norm.
  
      The trace distance measures how close two quantum states are. In particular, it upper-bounds
      the probability of distinguishing two quantum states.
  
      Args:
          qnode0 (QNode): A :class:`.QNode` returning a :func:`~pennylane.state`.
          qnode1 (QNode): A :class:`.QNode` returning a :func:`~pennylane.state`.
          wires0 (Sequence[int]): the subsystem of the first QNode.
          wires1 (Sequence[int]): the subsystem of the second QNode.
  
      Returns:
          func: A function that takes as input the joint arguments of the two QNodes,
          and returns the trace distance between their output states.
  
      **Example**
  
      Consider the following QNode:
  
      .. code-block:: python
  
          dev = qml.device('default.qubit', wires=2)
  
          @qml.qnode(dev)
          def circuit(param):
              qml.RY(param, wires=0)
              qml.CNOT(wires=[0, 1])
              return qml.state()
  
      The ``qml.qinfo.trace_distance`` transform can be used to compute the trace distance
      between the output states of the QNode:
  
      >>> trace_distance_circuit = qml.qinfo.trace_distance(circuit, circuit, wires0=[0], wires1=[0])
  
      The returned function takes two tuples as input, the first being the arguments to the
      first QNode and the second being the arguments to the second QNode:
  
      >>> x, y = np.array(0.4), np.array(0.6)
      >>> trace_distance_circuit((x,), (y,))
      0.047862689546603415
  
      This transform is fully differentiable:
  
      .. code-block:: python
  
          def wrapper(x, y):
              return trace_distance_circuit((x,), (y,))
  
      >>> wrapper(x, y)
      0.047862689546603415
      >>> qml.grad(wrapper)(x, y)
      (tensor(-0.19470917, requires_grad=True),
       tensor(0.28232124, requires_grad=True))
      """
  
      if len(wires0) != len(wires1):
          raise qml.QuantumFunctionError(
              "The two states must have the same number of wires."
          )
  
      state_qnode0 = qml.qinfo.reduced_dm(qnode0, wires=wires0)
      state_qnode1 = qml.qinfo.reduced_dm(qnode1, wires=wires1)
  
      def evaluate_trace_distance(all_args0=None, all_args1=None):
          """Wrapper used for evaluation of the trace distance between two states computed from
          QNodes. It allows giving the args and kwargs to each :class:`.QNode`.
  
          Args:
              all_args0 (tuple): Tuple containing the arguments (*args, kwargs) of the first :class:`.QNode`.
              all_args1 (tuple): Tuple containing the arguments (*args, kwargs) of the second :class:`.QNode`.
  
          Returns:
              float: Trace distance between two quantum states
          """
          if not isinstance(all_args0, tuple) and all_args0 is not None:
              all_args0 = (all_args0,)
  
          if not isinstance(all_args1, tuple) and all_args1 is not None:
              all_args1 = (all_args1,)
  
          # If no all_args is given, evaluate the QNode without args
          if all_args0 is not None:
              # Handle a dictionary as last argument
              if isinstance(all_args0[-1], dict):
                  args0 = all_args0[:-1]
                  kwargs0 = all_args0[-1]
              else:
                  args0 = all_args0
                  kwargs0 = {}
              state0 = state_qnode0(*args0, **kwargs0)
          else:
              # No args
              state0 = state_qnode0()
  
          # If no all_args is given, evaluate the QNode without args
          if all_args1 is not None:
              # Handle a dictionary as last argument
              if isinstance(all_args1[-1], dict):
                  args1 = all_args1[:-1]
                  kwargs1 = all_args1[-1]
              else:
                  args1 = all_args1
                  kwargs1 = {}
              state1 = state_qnode1(*args1, **kwargs1)
          else:
              # No args
              state1 = state_qnode1()
  
          # From the two generated states, compute the trace distance
          return qml.math.trace_distance(state0, state1)
  
      return evaluate_trace_distance
  
imports: from functools import partial
  from typing import Callable, Sequence
  import pennylane
  from pennylane.tape import QuantumTape
  from pennylane.devices import DefaultQubit, DefaultQubitLegacy, DefaultMixed
  from pennylane.measurements import StateMP, DensityMatrixMP
  from pennylane.gradients import adjoint_metric_tensor, metric_tensor
  from pennylane import transform
label_desc: Use image node_id 18 for calling a global function with example usage: trace_distance(qnode0, qnode1, wires0, wires1) and returns: evaluate_trace_distance, qml