[BUG] [can't fix] coeff * op errors out with autograd derivatives #6972
Description
Expected behavior
H = X(0) + Y(0) + Z(0)
dev = qml.device("default.qubit")
@qml.qnode(dev)
def func(x, y, z):
qml.exp(-1j * x * X(0))
qml.exp(-1j * y * Y(0))
qml.exp(-1j * z * Z(0))
return qml.expval(H)
x = jnp.array(0.5)
y = jnp.array(0.5)
z = jnp.array(0.5)
jax.grad(func)(x, y, z)
# Array(-2.5406466, dtype=float32, weak_type=True)
Actual behavior
import pennylane as qml
import pennylane.numpy as pnp
from pennylane import X, Y, Z, I
H = X(0) + Y(0) + Z(0)
dev = qml.device("default.qubit")
@qml.qnode(dev)
def func(x, y, z):
qml.exp(-1j * x * X(0))
qml.exp(-1j * y * Y(0))
qml.exp(-1j * z * Z(0))
return qml.expval(H)
x = pnp.array(0.5, requires_grad=True)
y = pnp.array(0.5, requires_grad=True)
z = pnp.array(0.5, requires_grad=True)
qml.grad(func)(x, y, z)...
Cell In[6], line 7
5 @qml.qnode(dev)
6 def func(x, y, z):
----> 7 qml.exp(-1j * x * X(0))
8 qml.exp(-1j * y * Y(0))
9 qml.exp(-1j * z * Z(0))
File ~/virtualenvs/pennylane/lib/python3.11/site-packages/autograd/numpy/numpy_boxes.py:28, in ArrayBox.__mul__(self, other)
---> 28 def __mul__(self, other): return anp.multiply(self, other)
File ~/virtualenvs/pennylane/lib/python3.11/site-packages/autograd/tracer.py:46, in primitive.<locals>.f_wrapped(*args, **kwargs)
44 ans = f_wrapped(*argvals, **kwargs)
45 node = node_constructor(ans, f_wrapped, argvals, kwargs, argnums, parents)
---> 46 return new_box(ans, trace, node)
47 else:
48 return f_raw(*args, **kwargs)
File ~/virtualenvs/pennylane/lib/python3.11/site-packages/autograd/tracer.py:120, in new_box(value, trace, node)
118 return box_type_mappings[type(value)](value, trace, node)
119 except KeyError:
--> 120 raise TypeError("Can't differentiate w.r.t. type {}".format(type(value)))
TypeError: Can't differentiate w.r.t. type <class 'pennylane.ops.op_math.sprod.SProd'>
Additional information
Would expect qml.exp to be differentiable
Source code
Tracebacks
System information
Name: PennyLane
Version: 0.41.0.dev18
Summary: PennyLane is a cross-platform Python library for quantum computing, quantum machine learning, and quantum chemistry. Train a quantum computer the same way as a neural network.
Home-page: https://github.com/PennyLaneAI/pennylane
Author:
Author-email:
License: Apache License 2.0
Location: /Users/korbinian.kottmann/virtualenvs/pennylane/lib/python3.11/site-packages
Editable project location: /Users/korbinian.kottmann/Xanadu/pennylane
Requires: appdirs, autograd, autoray, cachetools, diastatic-malt, networkx, numpy, packaging, pennylane-lightning, requests, rustworkx, scipy, tomlkit, typing_extensions
Required-by: PennyLane_Lightning
Platform info: macOS-15.3.1-arm64-arm-64bit
Python version: 3.11.11
Numpy version: 1.26.4
Scipy version: 1.15.1
Installed devices:
- default.clifford (PennyLane-0.41.0.dev18)
- default.gaussian (PennyLane-0.41.0.dev18)
- default.mixed (PennyLane-0.41.0.dev18)
- default.qubit (PennyLane-0.41.0.dev18)
- default.qutrit (PennyLane-0.41.0.dev18)
- default.qutrit.mixed (PennyLane-0.41.0.dev18)
- default.tensor (PennyLane-0.41.0.dev18)
- null.qubit (PennyLane-0.41.0.dev18)
- reference.qubit (PennyLane-0.41.0.dev18)
- lightning.qubit (PennyLane_Lightning-0.40.0)Existing GitHub issues
- I have searched existing GitHub issues to make sure the issue does not already exist.