I’m thirsty for simulate n-qubie GHZ state in pennylane and I wanna ask how to simulate it in pennylane.
Hey @DonaldTrump! Welcome to the forum and love the enthusiasm 
I highly recommend that you check out some of our introductory content, of which we have many different offerings depending on how you like to learn 
:
- Codebook: This is our free-to-access textbook that also has code exercises to help you learn PennyLane alongside traditional quantum computing, information, etc. Check it out here: https://codebook.xanadu.ai/
- Demos: We have a ton of demos on our website that are really really great
. Check them out here: Getting Started | PennyLane Demos. Might be a good idea to start with this one: Basic tutorial: qubit rotation | PennyLane Demos - Videos: We recently launched a dedicated PennyLane YouTube channel and we have a beginner video about how PennyLane works here: https://youtu.be/uCm027_jvZ0
To answer your question, though, there are a few ways you can prep a GHZ state in PennyLane:
- Gates: The GHZ state can be made with a Hadamard gate and a couple CNOTs
To do this in PennyLane, you just place the gates in a QNode and off you go!
import pennylane as qml
dev = qml.device("default.qubit")
@qml.qnode(dev)
def ghz():
qml.Hadamard(0)
qml.CNOT(wires=[0, 1])
qml.CNOT(wires=[1, 2])
return qml.state()
ghz()
tensor([0.70710678+0.j, 0. +0.j, 0. +0.j, 0. +0.j,
0. +0.j, 0. +0.j, 0. +0.j, 0.70710678+0.j], requires_grad=True)
- “Direct” state prep: You can directly encode the state into the circuit like this:
import pennylane.numpy as np
@qml.qnode(dev)
def ghz():
qml.StatePrep(np.array([1/np.sqrt(2), 0, 0, 0, 0, 0, 0, 1/np.sqrt(2)]), wires=range(3))
return qml.state()
ghz()
tensor([0.70710678+0.j, 0. +0.j, 0. +0.j, 0. +0.j,
0. +0.j, 0. +0.j, 0. +0.j, 0.70710678+0.j], requires_grad=True)
Anyway, if this is the start of your PennyLane journey, we’re glad to have you on board! Feel free to post any questions here that you may have along the way 
@isaacdevlugt Please accept my heartfelt thanks!!You help me a lot!
1 Like
My pleasure! Glad I could help