Basic Quantum Computing - Getting started with Qiskit

Now, we’ve learnt a little bit about quantum computing let’s get started by programming one.

Python

We’re going to be using the Python programming language to start writing quantum programs. So I’m going to assume you know a little bit of Python and have it installed locally.

I’m also going to assume that you have a little bit of knowledge of how to use the terminal (or command prompt on Windows).

So let’s start by creating a folder to store our quantum programs:

mkdir QuantumPrograms && cd QuantumPrograms

Now let’s setup a virtual environment. This means all the libraries we install will only be used for this project.

To do this run:

python3-m venv ./venv
source venv/bin/activate

Finally, let’s install Qiskit which is the library we’ll use to start working with Quantum Computers.

pip install qiskit
pip install qiskit_aer

Writing our first quantum program

Let’s create a file called first_quantum_programme.py and let’s add the following contents:

from qiskit import QuantumCircuit, QuantumRegister, transpile
from qiskit_aer import AerSimulator

These two lines are going to import all the things we’ll need for writing our program.

Next, let’s add:

register = QuantumRegister(1)
circuit = QuantumCircuit(register)

This creates a quantum register with 1 qubit. (A quantum register is just a collection of qubits). In Qiskit, all registers start with all the qubits set to 0. It then creates a circuit containing our register

Now let’s add:

circuit.x(register[0])

This line applies an X gate (e.g. a NOT gate) to the first qubit in our register

Now we can add

circuit.measure_all()

This will measure all the qubits in our circuit

Finally, let’s add:

simulator = AerSimulator()

compiled_circuit = transpile(circuit, simulator)

job = simulator.run(compiled_circuit, shots=1000)

result = job.result()
counts = result.get_counts(compiled_circuit)

print(counts)

This will create a simulator that simulates a quantum computer. It will then take our circuit and convert it into a form that the simulator can understand. Then it will run 1000 times on the simulator. Finally, we get the results of running our programme on the simulator.

So in total, our programme should look like this:

from qiskit import QuantumCircuit, QuantumRegister, transpile
from qiskit_aer import AerSimulator


register = QuantumRegister(1)
circuit = QuantumCircuit(register)

circuit.x(register[0])

circuit.measure_all()

simulator = AerSimulator()

compiled_circuit = transpile(circuit, simulator)

job = simulator.run(compiled_circuit, shots=1000)

result = job.result()
counts = result.get_counts(compiled_circuit)

print(counts)

Now we can run it using the following command:

python3 first_quantum_programme.py

And we should get the following output:

{'1': 1000}

This tells us we got the result 1 a thousand times which is exactly what we’d expect because we started with a qubit set to 0 then applied a NOT gate to change it to a 1.