# Add control qubits to states **URL:** \ **Category:** Strawberry Fields\ **Created:** [March 21, 2022, 10:03am UTC](https://discuss.pennylane.ai/t/add-control-qubits-to-states/1744 "2022-03-21T10:03:58Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![sassan\_moradi](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/sassan_moradi/32/422_2.png) [@sassan\_moradi](https://discuss.pennylane.ai/u/sassan_moradi)\ **Post date:** [March 21, 2022, 10:03am UTC](https://discuss.pennylane.ai/t/add-control-qubits-to-states/1744/1 "2022-03-21T10:03:58Z")
I want to add two control qubits to a statepreparation method. how can i do it? here is the code ```auto import numpy as np import pennylane as qml num_qubits = 4 dev = qml.device('default.qubit', wires=num_qubits, shots=8192) def Stateper(X): return qml.templates.MottonenStatePreparation(X, wires=[2, 3]) @qml.qnode(dev) def circuit(X): qml.ControlledQubitUnitary(Stateper(X), control_wires=[0, 1], wires=[3, 4], control_values='11') # control qubits = [0, 1] and target=[3, 4] return qml.state() X = [1/2, 1/2, 1/2, 1/2] print(circuit(X)) ``` ---
**Author:** ![CatalinaAlbornoz](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/catalinaalbornoz/32/1196_2.png) [@CatalinaAlbornoz](https://discuss.pennylane.ai/u/CatalinaAlbornoz)\ **Post date:** [March 21, 2022, 11:01pm UTC](https://discuss.pennylane.ai/t/add-control-qubits-to-states/1744/2 "2022-03-21T23:01:36Z")
Hi @sassan_moradi, I’m not sure what’s the exact error you’re getting but I think the issue is that the wires has to be an iterable. This means that it needs to be something like `wires=range(3)`. In your case for `wires=[2,3]` you would need `wires=range(2,4)`. Please let me know if this solves your problem! If not please share the error message you’re getting. ---
**Author:** ![sassan\_moradi](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/sassan_moradi/32/422_2.png) [@sassan\_moradi](https://discuss.pennylane.ai/u/sassan_moradi)\ **Post date:** [April 1, 2022, 6:32am UTC](https://discuss.pennylane.ai/t/add-control-qubits-to-states/1744/3 "2022-04-01T06:32:35Z")
if len(U) != target\_dim: TypeError: object of type ‘MottonenStatePreparation’ has no len() ---
**Author:** ![CatalinaAlbornoz](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/catalinaalbornoz/32/1196_2.png) [@CatalinaAlbornoz](https://discuss.pennylane.ai/u/CatalinaAlbornoz)\ **Post date:** [April 1, 2022, 3:01pm UTC](https://discuss.pennylane.ai/t/add-control-qubits-to-states/1744/4 "2022-04-01T15:01:38Z")
Hi @sassan_moradi, I couldn’t replicate your error but using the [ctrl](https://pennylane.readthedocs.io/en/stable/code/api/pennylane.ctrl.html) function you can achieve the result you want in an easier way. The following code should work for you: ``` import pennylane as qml from pennylane import numpy as np num_qubits = 4 dev = qml.device('default.qubit', wires=num_qubits, shots=8192) def Stateper(X): return qml.MottonenStatePreparation(X, wires=range(2,4)) op = qml.ctrl(Stateper,control=[0,1]) X = np.array([1/2, 1/2, 1/2, 1/2]) @qml.qnode(dev) def circuit(X): op(X) return qml.state() print(circuit(X)) print(qml.draw_mpl(circuit)(X)) ``` You will notice a few things: - I imported numpy directly from PennyLane. This is important, specially when you need to set your parameters as trainable or not. - In the MottonenStatePreparation the wires are defined as a range because this value needs to be an iterable. - I used the ctrl function to specify the control qubits. This is equivalent to `op1 = qml.ctrl(qml.ctrl(Stateper, 1), 0)` - X is set as a numpy array. If you don’t set it this way it will still work but when you use qml.draw\_mpl you won’t see the details of the circuit. Please let me know if this is what you were looking for! If this code doesn’t work try making sure that you’re using the latest PennyLane version. If it still doesn’t work please let me know. ---
**Author:** ![sassan\_moradi](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/sassan_moradi/32/422_2.png) [@sassan\_moradi](https://discuss.pennylane.ai/u/sassan_moradi)\ **Post date:** [April 1, 2022, 3:16pm UTC](https://discuss.pennylane.ai/t/add-control-qubits-to-states/1744/5 "2022-04-01T15:16:40Z")
many thanks for your useful response. i will try it and get back to you. ---
**Author:** ![sassan\_moradi](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/sassan_moradi/32/422_2.png) [@sassan\_moradi](https://discuss.pennylane.ai/u/sassan_moradi)\ **Post date:** [April 1, 2022, 3:26pm UTC](https://discuss.pennylane.ai/t/add-control-qubits-to-states/1744/6 "2022-04-01T15:26:54Z")
how can i use ctrl function, if i want to have control\_value = ‘01’? but my problem is still with control value. ---
**Author:** ![CatalinaAlbornoz](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/catalinaalbornoz/32/1196_2.png) [@CatalinaAlbornoz](https://discuss.pennylane.ai/u/CatalinaAlbornoz)\ **Post date:** [April 4, 2022, 10:32pm UTC](https://discuss.pennylane.ai/t/add-control-qubits-to-states/1744/7 "2022-04-04T22:32:31Z")
Hi @sassan_moradi, I’m not understanding your question. Did the code example show you an error? Or do you want a different functionality? In the example above the control qubits are ‘0’ and ‘1’. (`op = qml.ctrl(Stateper,control=[0,1])`) The ctrl function receives a python function and the control wires as parameters and it returns the controlled version of the function. You can read more about it [here](https://pennylane.readthedocs.io/en/stable/code/api/pennylane.ctrl.html). Please let me know if this answers your question or if it doesn’t please provide more details or an example of what you mean. ---
**Author:** ![sassan\_moradi](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/sassan_moradi/32/422_2.png) [@sassan\_moradi](https://discuss.pennylane.ai/u/sassan_moradi)\ **Post date:** [April 5, 2022, 8:08am UTC](https://discuss.pennylane.ai/t/add-control-qubits-to-states/1744/8 "2022-04-05T08:08:33Z")
the example was true. i could run it successfully. But i want different functionality. for example, we know the quantum circuit for Möttonen state and as far as i know qml.ControlledQubitUnitary only take a matrix (gate) as an argument. Your example only consider control value = ‘11’. i want to also have control value = ‘01’. One way that i can do in qiskit is to design quantum circuit and then use convert to gate method which can convert a quantum circuit to a unitary matrix. I don’t know if Pennylane can do it or not. ---
**Author:** ![CatalinaAlbornoz](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/catalinaalbornoz/32/1196_2.png) [@CatalinaAlbornoz](https://discuss.pennylane.ai/u/CatalinaAlbornoz)\ **Post date:** [April 5, 2022, 6:04pm UTC](https://discuss.pennylane.ai/t/add-control-qubits-to-states/1744/9 "2022-04-05T18:04:18Z")
Oh I see now @sassan_moradi. You can use `qml.matrix` to get the matrix representation of your quantum circuit. [Here](https://pennylane.readthedocs.io/en/latest/code/api/pennylane.matrix.html) in the “usage details” section you can see how to use it. On the other hand, if you want your control value to be ‘01’ then you only need to add a PauliX gate to your first qubit before you apply the control. So the code above can remain the same except that your circuit function is now: ``` def circuit(X): qml.PauliX(0) op(X) return qml.state() ``` Please let me know if this helps! ---
**Author:** ![sassan\_moradi](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/sassan_moradi/32/422_2.png) [@sassan\_moradi](https://discuss.pennylane.ai/u/sassan_moradi)\ **Post date:** [April 6, 2022, 8:26am UTC](https://discuss.pennylane.ai/t/add-control-qubits-to-states/1744/10 "2022-04-06T08:26:47Z")
many thanks. i think using PauliX gate can be the only solution for it at this moment. ---
**Author:** ![CatalinaAlbornoz](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/catalinaalbornoz/32/1196_2.png) [@CatalinaAlbornoz](https://discuss.pennylane.ai/u/CatalinaAlbornoz)\ **Post date:** [April 7, 2022, 12:00am UTC](https://discuss.pennylane.ai/t/add-control-qubits-to-states/1744/11 "2022-04-07T00:00:25Z")
Hi @sassan_moradi, you could always create a state-preparation function where you input a string and it performs the necessary PauliX gates according to your needs. It really depends on how automated you need this to be but you could even use an embedding template or a custom embedding to generate rotations according to the values that you want as a control. The [Basis Embedding](https://pennylane.readthedocs.io/en/stable/code/api/pennylane.BasisEmbedding.html) in particular may be very useful for you. Let me know if this helps! ---
**Author:** ![sassan\_moradi](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/sassan_moradi/32/422_2.png) [@sassan\_moradi](https://discuss.pennylane.ai/u/sassan_moradi)\ **Post date:** [April 7, 2022, 12:02pm UTC](https://discuss.pennylane.ai/t/add-control-qubits-to-states/1744/12 "2022-04-07T12:02:48Z")
Many thanks for your instructive responses. They were very helpful. ---
**Author:** ![CatalinaAlbornoz](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/catalinaalbornoz/32/1196_2.png) [@CatalinaAlbornoz](https://discuss.pennylane.ai/u/CatalinaAlbornoz)\ **Post date:** [April 7, 2022, 8:47pm UTC](https://discuss.pennylane.ai/t/add-control-qubits-to-states/1744/13 "2022-04-07T20:47:00Z")
I’m glad I could help @sassan_moradi!