Qiskit Cheatsheet (WIP)

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This page is designed to be an example-based reference for using the various Qiskit classes, functions, and methods we have discussed throughout the guide.

Circuit Basics

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Qubit Creation

The QuantumRegister object takes two arguments: the number of qubits you want to use, and a label:

qubit0 = QuantumRegister(1, name = "qubit0")

The ClassicalRegister object takes two arguments: the number of bits you want to use, and a label:

classic_bit0 = ClassicalRegister(1, name = "classic_bit0")

Circuit Creation

The QuantumCircuit object takes your QuantumRegister and ClassicalRegister objects as arguments and creates a circuit:

circuit = QuantumCircuit(qubit0, classic_bit0)

Alternatively, you can pass in integer values if you do not want to create separate QuantumRegister/ClassicalRegister objects:

circuit = QuantumCircuit(1, 1)

Circuit Methods

Using your QuantumCircuit object, you can initialize your qubit state with the initialize() method:

state = [0, 1] # This is a vector in the form of a list: [alpha, beta]
circuit.initialize(state, qubit0) # Initializes qubit0 to the defined state

To measure, you can use measure():

circuit.measure(qubit0, classic_bit0) # Perform Z-measurement on qubit0

To visualize your circuit, you can use draw():

circuit.draw()

Fundamental Gates

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Hadamard Gate

The h() method takes a qubit as an argument and applies a Hadamard gate to it:

circuit.h(qubit) # Applies a Hadamard gate to qubit

X-gate

The x() method takes a qubit as an argument and applies an X-gate to it:

circuit.x(qubit) # Applies an X-gate to qubit

Y-gate

The y() method takes a qubit as an argument and applies a Y-gate to it:

circuit.y(qubit) # Applies a Y-gate to qubit

Z-gate

The z() method takes a qubit as an argument and applies a Z-gate to it:

circuit.z(qubit) # Applies a Z-gate to qubit

CNOT gate

The cx() method takes a control qubit (for the first argument), and a target qubit (for the second argument) and applies a CNOT gate to them:

circuit.cx(control, target) # Applies a CNOT using the control and target qubits

R(phi)-gate

The rz() method takes one qubit and phi radians as arguments and applies an R(phi)-gate to the qubit:

circuit.rz(phi, qubit) # where phi is in radians

S-gate and its conjugate transpose

The s() method takes a qubit as an argument and applies an S-gate to it:

circuit.s(qubit)

The conjugate transpose, the sdg() method, also takes a qubit as an argument and applies an S-dagger gate to it:

circuit.sdg(qubit)

Entanglement with the Bell Pair function

def bellPair(circuit, qubit0, qubit1): # entangles qubits
    circuit.h(qubit0) 
    circuit.cx(qubit0,qubit1) 

Simulator Functions

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Qasm

def simulateQasm(circuit):
    backend = Aer.get_backend('qasm_simulator') # Loads the qasm simulator
    job = execute(circuit, backend, shots=1024).result().get_counts() # Retrives results from simulation
    return plot_histogram(data)

Statevector Simulator

def simulateStateVector(circuit):
    backend = Aer.get_backend('statevector_simulator') # Loads the statevector simulator
    data = execute(circuit, backend).result().get_statevector() # Retrives results and statevector from simulation
    return plot_histogram(data) # Presents data with a histogram

Bloch Sphere Simulator

def simulateBlochSphere(circuit):
    backend = Aer.get_backend('statevector_simulator') # Loads the statevector simulator
    job = execute(circuit,backend).result().get_statevector() # Retrives results and statevector from simulation
    return plot_bloch_multivector(job) # Presents the Bloch sphere