Learn PENNYLANE with Real Code Examples

import pennylane as qml
from pennylane import numpy as np

# Define a 2-qubit device
dev = qml.device('default.qubit', wires=2)

# Define a quantum circuit
@qml.qnode(dev)
def circuit(params):
    qml.RX(params[0], wires=0)
    qml.RY(params[1], wires=1)
    qml.CNOT(wires=[0,1])
    return qml.expval(qml.PauliZ(0)), qml.expval(qml.PauliZ(1))

# Evaluate the circuit
params = np.array([0.1, 0.2])
print(circuit(params))

A minimal PennyLane example defining a 2-qubit quantum circuit, applying gates, and computing expectation values.

import pennylane as qml

dev = qml.device('default.qubit', wires=2)

@qml.qnode(dev)
def bell_state():
    hadamard(0)
    qml.CNOT(wires=[0,1])
    return qml.state()

print(bell_state())

Creates a Bell state using a Hadamard and CNOT gate.

import pennylane as qml

dev = qml.device('default.qubit', wires=3)

@qml.qnode(dev)
def ghz_state():
    qml.Hadamard(wires=0)
    qml.CNOT(wires=[0,1])
    qml.CNOT(wires=[0,2])
    return qml.state()

print(ghz_state())

Generates a 3-qubit GHZ state.

import pennylane as qml
from pennylane import numpy as np

dev = qml.device('default.qubit', wires=3)

@qml.qnode(dev)
def teleport(msg_state):
    qml.QubitStateVector(msg_state, wires=0)
    qml.Hadamard(wires=1)
    qml.CNOT(wires=[1,2])
    qml.CNOT(wires=[0,1])
    qml.Hadamard(wires=0)
    return qml.state()

msg_state = [1,0]
print(teleport(msg_state))

Implements the quantum teleportation protocol.

import pennylane as qml
from pennylane import numpy as np

dev = qml.device('default.qubit', wires=2)

@qml.qnode(dev)
def var_circuit(params):
    qml.RX(params[0], wires=0)
    qml.RY(params[1], wires=1)
    qml.CNOT(wires=[0,1])
    return qml.expval(qml.PauliZ(0))

params = np.array([0.5, 0.3])
print(var_circuit(params))

A simple variational quantum circuit using RX and RY rotations.

import pennylane as qml

dev = qml.device('default.qubit', wires=2)

@qml.qnode(dev)
def cphase_example():
    qml.Hadamard(wires=0)
    qml.CPhase(np.pi/2, wires=[0,1])
    return qml.state()

print(cphase_example())

Applies a controlled phase rotation between two qubits.

import pennylane as qml
from pennylane import numpy as np

dev = qml.device('default.qubit', wires=3)

@qml.qnode(dev)
def swap_test(state1, state2):
    qml.Hadamard(wires=0)
    qml.QubitStateVector(state1, wires=1)
    qml.QubitStateVector(state2, wires=2)
    qml.CSWAP(wires=[0,1,2])
    qml.Hadamard(wires=0)
    return qml.expval(qml.PauliZ(0))

state1 = [1,0]
state2 = [0,1]
print(swap_test(state1, state2))

Performs a swap test to compute the overlap of two quantum states.

import pennylane as qml
from pennylane import numpy as np

dev = qml.device('default.qubit', wires=1)

@qml.qnode(dev)
def circuit(x):
    qml.RX(x, wires=0)
    return qml.expval(qml.PauliZ(0))

x = 0.5
grad_fn = qml.grad(circuit)
print(grad_fn(x))

Computes the gradient of a simple variational circuit.

import pennylane as qml
import numpy as np

dev = qml.device('default.qubit', wires=3)

def qft3():
    qml.Hadamard(wires=0)
    qml.CPhase(np.pi/2, wires=[0,1])
    qml.CPhase(np.pi/4, wires=[0,2])
    qml.Hadamard(wires=1)
    qml.CPhase(np.pi/2, wires=[1,2])
    qml.Hadamard(wires=2)

@qml.qnode(dev)
def qft_circuit():
    qft3()
    return qml.state()

print(qft_circuit())

Implements a simple 3-qubit quantum Fourier transform.

import pennylane as qml

dev = qml.device('default.qubit', wires=2)

@qml.qnode(dev)
def measure_circuit():
    qml.Hadamard(wires=0)
    qml.CNOT(wires=[0,1])
    return qml.sample()

print(measure_circuit())

Applies gates and measures qubits in the computational basis.