# DeviceError: Observable QuadX not supported on device strawberryfields.fock **URL:** \ **Category:** PennyLane Help\ **Created:** [March 1, 2024, 9:17am UTC](https://discuss.pennylane.ai/t/deviceerror-observable-quadx-not-supported-on-device-strawberryfields-fock/4197 "2024-03-01T09:17:00Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![RX1](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/rx1/32/698_2.png) [@RX1](https://discuss.pennylane.ai/u/RX1)\ **Post date:** [March 1, 2024, 9:17am UTC](https://discuss.pennylane.ai/t/deviceerror-observable-quadx-not-supported-on-device-strawberryfields-fock/4197/1 "2024-03-01T09:17:01Z")
When I used this demo, > **[Function fitting with a photonic quantum neural network | PennyLane Demos](https://pennylane.ai/qml/demos/quantum_neural_net/)** > > Fit to noisy data with a variational quantum circuit. the errors are occured: ```auto --------------------------------------------------------------------------- DeviceError Traceback (most recent call last) Cell In[12], line 5 3 var = var_init 4 for it in range(500): ----> 5 (var, _, _), _cost = opt.step_and_cost(cost, var, X, Y) 6 print("Iter: {:5d} | Cost: {:0.7f} ".format(it, _cost)) File d:\miniconda3\lib\site-packages\pennylane\optimize\gradient_descent.py:64, in GradientDescentOptimizer.step_and_cost(self, objective_fn, grad_fn, *args, **kwargs) 44 def step_and_cost(self, objective_fn, *args, grad_fn=None, **kwargs): 45 """Update trainable arguments with one step of the optimizer and return the corresponding 46 objective function value prior to the step. 47 (...) 61 If single arg is provided, list [array] is replaced by array. 62 """ ---> 64 g, forward = self.compute_grad(objective_fn, args, kwargs, grad_fn=grad_fn) 65 new_args = self.apply_grad(g, args) 67 if forward is None: File d:\miniconda3\lib\site-packages\pennylane\optimize\gradient_descent.py:122, in GradientDescentOptimizer.compute_grad(objective_fn, args, kwargs, grad_fn) 104 r"""Compute gradient of the objective function at the given point and return it along with 105 the objective function forward pass (if available). 106 (...) 119 will not be evaluted and instead ``None`` will be returned. 120 """ 121 g = get_gradient(objective_fn) if grad_fn is None else grad_fn --> 122 grad = g(*args, **kwargs) 123 forward = getattr(g, "forward", None) 125 num_trainable_args = sum(getattr(arg, "requires_grad", False) for arg in args) File d:\miniconda3\lib\site-packages\pennylane\_grad.py:165, in grad. __call__ (self, *args, **kwargs) 162 self._forward = self._fun(*args, **kwargs) 163 return () --> 165 grad_value, ans = grad_fn(*args, **kwargs) # pylint: disable=not-callable 166 self._forward = ans 168 return grad_value File d:\miniconda3\lib\site-packages\autograd\wrap_util.py:20, in unary_to_nary..nary_operator..nary_f(*args, **kwargs) 18 else: 19 x = tuple(args[i] for i in argnum) ---> 20 return unary_operator(unary_f, x, *nary_op_args, **nary_op_kwargs) File d:\miniconda3\lib\site-packages\pennylane\_grad.py:183, in grad._grad_with_forward(fun, x) 177 @staticmethod 178 @unary_to_nary 179 def _grad_with_forward(fun, x): 180 """This function is a replica of ``autograd.grad``, with the only 181 difference being that it returns both the gradient *and* the forward pass 182 value.""" --> 183 vjp, ans = _make_vjp(fun, x) # pylint: disable=redefined-outer-name 185 if vspace(ans).size != 1: 186 raise TypeError( 187 "Grad only applies to real scalar-output functions. " 188 "Try jacobian, elementwise_grad or holomorphic_grad." 189 ) File d:\miniconda3\lib\site-packages\autograd\core.py:10, in make_vjp(fun, x) 8 def make_vjp(fun, x): 9 start_node = VJPNode.new_root() ---> 10 end_value, end_node = trace(start_node, fun, x) 11 if end_node is None: 12 def vjp(g): return vspace(x).zeros() File d:\miniconda3\lib\site-packages\autograd\tracer.py:10, in trace(start_node, fun, x) 8 with trace_stack.new_trace() as t: 9 start_box = new_box(x, t, start_node) ---> 10 end_box = fun(start_box) 11 if isbox(end_box) and end_box._trace == start_box._trace: 12 return end_box._value, end_box._node File d:\miniconda3\lib\site-packages\autograd\wrap_util.py:15, in unary_to_nary..nary_operator..nary_f..unary_f(x) 13 else: 14 subargs = subvals(args, zip(argnum, x)) ---> 15 return fun(*subargs, **kwargs) Cell In[6], line 2, in cost(var, features, labels) 1 def cost(var, features, labels): ----> 2 preds = [quantum_neural_net(var, x) for x in features] 3 return square_loss(labels, preds) Cell In[6], line 2, in (.0) 1 def cost(var, features, labels): ----> 2 preds = [quantum_neural_net(var, x) for x in features] 3 return square_loss(labels, preds) File d:\miniconda3\lib\site-packages\pennylane\qnode.py:1039, in QNode. __call__ (self, *args, **kwargs) 1034 full_transform_program._set_all_argnums( 1035 self, args, kwargs, argnums 1036 ) # pylint: disable=protected-access 1038 # pylint: disable=unexpected-keyword-arg -> 1039 res = qml.execute( 1040 (self._tape,), 1041 device=self.device, 1042 gradient_fn=self.gradient_fn, 1043 interface=self.interface, 1044 transform_program=full_transform_program, 1045 config=config, 1046 gradient_kwargs=self.gradient_kwargs, 1047 override_shots=override_shots, 1048 **self.execute_kwargs, 1049 ) 1051 res = res[0] 1053 # convert result to the interface in case the qfunc has no parameters File d:\miniconda3\lib\site-packages\pennylane\interfaces\execution.py:808, in execute(tapes, device, gradient_fn, interface, transform_program, config, grad_on_execution, gradient_kwargs, cache, cachesize, max_diff, override_shots, expand_fn, max_expansion, device_batch_transform, device_vjp) 803 ml_boundary_execute = _get_ml_boundary_execute( 804 interface, _grad_on_execution, config.use_device_jacobian_product 805 ) 807 if interface in jpc_interfaces: --> 808 results = ml_boundary_execute(tapes, execute_fn, jpc, device=device) 809 else: 810 results = ml_boundary_execute( 811 tapes, device, execute_fn, gradient_fn, gradient_kwargs, _n=1, max_diff=max_diff 812 ) File d:\miniconda3\lib\site-packages\pennylane\interfaces\autograd.py:147, in autograd_execute(tapes, execute_fn, jpc, device) 142 # pylint misidentifies autograd.builtins as a dict 143 # pylint: disable=no-member 144 parameters = autograd.builtins.tuple( 145 [autograd.builtins.list(t.get_parameters()) for t in tapes] 146 ) --> 147 return _execute(parameters, tuple(tapes), execute_fn, jpc) File d:\miniconda3\lib\site-packages\autograd\tracer.py:44, in primitive..f_wrapped(*args, **kwargs) 42 parents = tuple(box._node for _ , box in boxed_args) 43 argnums = tuple(argnum for argnum, _ in boxed_args) ---> 44 ans = f_wrapped(*argvals, **kwargs) 45 node = node_constructor(ans, f_wrapped, argvals, kwargs, argnums, parents) 46 return new_box(ans, trace, node) File d:\miniconda3\lib\site-packages\autograd\tracer.py:48, in primitive..f_wrapped(*args, **kwargs) 46 return new_box(ans, trace, node) 47 else: ---> 48 return f_raw(*args, **kwargs) File d:\miniconda3\lib\site-packages\pennylane\interfaces\autograd.py:168, in _execute(parameters, tapes, execute_fn, jpc) 150 @autograd.extend.primitive 151 def _execute( 152 parameters, (...) 155 jpc, 156 ): # pylint: disable=unused-argument 157 """Autodifferentiable wrapper around a way of executing tapes. 158 159 Args: (...) 166 167 """ --> 168 return execute_fn(tapes) File d:\miniconda3\lib\site-packages\pennylane\interfaces\execution.py:261, in _make_inner_execute..inner_execute(tapes, **_) 259 if numpy_only: 260 tapes = tuple(qml.transforms.convert_to_numpy_parameters(t) for t in tapes) --> 261 return cached_device_execution(tapes) File d:\miniconda3\lib\site-packages\pennylane\interfaces\execution.py:383, in cache_execute..wrapper(tapes, **kwargs) 378 return (res, []) if return_tuple else res 380 else: 381 # execute all unique tapes that do not exist in the cache 382 # convert to list as new device interface returns a tuple --> 383 res = list(fn(tuple(execution_tapes.values()), **kwargs)) 385 final_res = [] 387 for i, tape in enumerate(tapes): File d:\miniconda3\lib\contextlib.py:79, in ContextDecorator. __call__..inner(*args, **kwds) 76 @wraps(func) 77 def inner(*args, **kwds): 78 with self._recreate_cm(): ---> 79 return func(*args, **kwds) File d:\miniconda3\lib\site-packages\pennylane\_device.py:532, in Device.batch_execute(self, circuits) 527 for circuit in circuits: 528 # we need to reset the device here, else it will 529 # not start the next computation in the zero state 530 self.reset() --> 532 res = self.execute(circuit.operations, circuit.measurements) 533 results.append(res) 535 if self.tracker.active: File d:\miniconda3\lib\site-packages\pennylane\_device.py:437, in Device.execute(self, queue, observables, parameters, **kwargs) 414 def execute(self, queue, observables, parameters=None, **kwargs): 415 """Execute a queue of quantum operations on the device and then measure the given observables. 416 417 For plugin developers: Instead of overwriting this, consider implementing a suitable subset of (...) 435 array[float]: measured value(s) 436 """ --> 437 self.check_validity(queue, observables) 438 self._op_queue = queue 439 self._obs_queue = observables File d:\miniconda3\lib\site-packages\pennylane\_device.py:1011, in Device.check_validity(self, queue, observables) 1008 observable_name = o.name 1010 if not self.supports_observable(observable_name): -> 1011 raise DeviceError( 1012 f"Observable {observable_name} not supported on device {self.short_name}" 1013 ) DeviceError: Observable QuadX not supported on device strawberryfields.fock ``` > qml.about() ```auto Name: PennyLane Version: 0.34.0 Summary: PennyLane is a Python quantum machine learning library by Xanadu Inc. Home-page: https://github.com/PennyLaneAI/pennylane Author: Author-email: License: Apache License 2.0 Location: d:\miniconda3\lib\site-packages Requires: appdirs, autograd, autoray, cachetools, networkx, numpy, pennylane-lightning, requests, rustworkx, scipy, semantic-version, toml, typing-extensions Required-by: PennyLane-Lightning, PennyLane-SF Platform info: Windows-10-10.0.22000-SP0 Python version: 3.9.1 Numpy version: 1.23.5 Scipy version: 1.12.0 Installed devices: - default.gaussian (PennyLane-0.34.0) - default.mixed (PennyLane-0.34.0) - default.qubit (PennyLane-0.34.0) - default.qubit.autograd (PennyLane-0.34.0) - default.qubit.jax (PennyLane-0.34.0) - default.qubit.legacy (PennyLane-0.34.0) - default.qubit.tf (PennyLane-0.34.0) - default.qubit.torch (PennyLane-0.34.0) - default.qutrit (PennyLane-0.34.0) - null.qubit (PennyLane-0.34.0) - strawberryfields.fock (PennyLane-SF-0.29.1) - strawberryfields.gaussian (PennyLane-SF-0.29.1) - strawberryfields.gbs (PennyLane-SF-0.29.1) - strawberryfields.remote (PennyLane-SF-0.29.1) - strawberryfields.tf (PennyLane-SF-0.29.1) - lightning.qubit (PennyLane-Lightning-0.34.0) ``` ---
**Author:** ![ludmilaaasb](https://avatars.discourse-cdn.com/v4/letter/l/d78d45/32.png) [@ludmilaaasb](https://discuss.pennylane.ai/u/ludmilaaasb)\ **Post date:** [March 1, 2024, 9:58am UTC](https://discuss.pennylane.ai/t/deviceerror-observable-quadx-not-supported-on-device-strawberryfields-fock/4197/2 "2024-03-01T09:58:59Z")
Hello @RX1 ! In the demo there is a warning: ![image](https://canada1.discourse-cdn.com/flex012/uploads/pennylane/original/2X/6/60529fdf00b102a78af3978be5a7394fe73ade84.png) It seems that in your current environment, the PennyLane installed version is 0.34. I suggest you create a clean environment with 0.29 version. I hope it helps! 😉