code: def _register_vjp(state0, state1):
      """
      Register the interface-specific custom VJP based on the interfaces of the given states
  
      This function is needed because we don't want to register the custom
      VJPs at PennyLane import time.
      """
      interface = qml.math.get_interface(state0, state1)
      if interface == "jax":
          _register_jax_vjp()
      elif interface == "torch":
          _register_torch_vjp()
      elif interface == "tensorflow":
          _register_tf_vjp()
  
file_path: pennylane/pennylane/math/fidelity.py
imports: from functools import lru_cache
  import autograd
  import autoray
  import pennylane
  from .utils import cast
  from .quantum import _check_density_matrix, _check_state_vector
label_desc: Use image node_id 3 for calling a global function with example usage: _register_vjp(state0, state1) without return types