From browser demos to real quantum code

01 · What is Qiskit?

A Python library for quantum circuits

Qiskit lets you build circuits out of the same gates you used in this series, simulate them, and send them to quantum computers. It's free, open source under the Apache 2.0 license, and the most widely used quantum programming toolkit.

02 · Install

Set up Qiskit in a few minutes

Use a virtual environment so Qiskit's packages stay separate from everything else on your machine.

1 · CHECK PYTHON (NEEDS 3.10 OR NEWER)

python --version

2 · CREATE A VIRTUAL ENVIRONMENT

python -m venv qenv

3a · ACTIVATE IT ON WINDOWS

qenv\Scripts\activate

3b · ACTIVATE IT ON macOS OR LINUX

source qenv/bin/activate

4 · INSTALL QISKIT

pip install qiskit

OPTIONAL · ADD PLOTTING SUPPORT FOR CIRCUIT DIAGRAMS AND HISTOGRAMS

pip install "qiskit[visualization]"

On some macOS and Linux systems the commands are python3 and pip3. Jupyter notebooks (pip install notebook) are a comfortable place to experiment.

03 · Your first circuit

Build the Bell state from Quantum 05

This program creates the entangled state |Φ⁺⟩ with the same two gates you used on page 05, then measures it 1,000 times on a simulator. No account or quantum hardware is needed.

BELL.PY

from qiskit import QuantumCircuit
from qiskit.primitives import StatevectorSampler

# Build the Bell state from Quantum 05: H on qubit 0, then CNOT from 0 to 1
qc = QuantumCircuit(2)
qc.h(0)
qc.cx(0, 1)
qc.measure_all()

print(qc.draw())          # text drawing of the circuit

# Run 1,000 shots on a simulator built into Qiskit
sampler = StatevectorSampler()
result = sampler.run([qc], shots=1000).result()
print(result[0].data.meas.get_counts())

OUTPUT (YOUR COUNTS WILL VARY SLIGHTLY)

        ┌───┐      ░ ┌─┐
   q_0: ┤ H ├──■───░─┤M├───
        └───┘┌─┴─┐ ░ └╥┘┌─┐
   q_1: ─────┤ X ├─░──╫─┤M├
             └───┘ ░  ║ └╥┘
meas: 2/══════════════╩══╩═
                      0  1
{'00': 507, '11': 493}

Peek at the amplitudes

On a simulator you can look at the state vector directly, something real hardware never allows. This checks the H-then-S result from the gate lab on page 04.

STATEVECTOR.PY

from qiskit import QuantumCircuit
from qiskit.quantum_info import Statevector

# Quantum 03-04: H then S on |0⟩ should land on |+i⟩ = (|0⟩ + i|1⟩)/√2
qc = QuantumCircuit(1)
qc.h(0)
qc.s(0)
print(Statevector(qc))

OUTPUT

Statevector([0.70710678+0.j        , 0.        +0.70710678j],
            dims=(2,))

Python writes the imaginary unit as j, so 0.70710678j is 0.707i, matching (|0⟩ + i|1⟩)/√2.

04 · Series-to-Qiskit map

Every gate in the series has a one-line Qiskit command

Challenges: rebuild the series in code

1. Verify the identity HZH = X from page 04: apply H, Z, H to |0⟩ and print the Statevector. You should get |1⟩.
2. Build all four Bell states from page 05. Hint: add qc.x() gates before the H and CNOT to change the input.
3. Recreate the interference demo from page 02: H, then H again, then measure. Then add qc.measure_all() between the two H gates and compare.
4. Write a one-qubit Deutsch algorithm (page 06 with n = 1) where the oracle is a CNOT. Is that function constant or balanced?

05 · Learn by video

The Qiskit YouTube channel

IBM's official Qiskit channel posts lectures, coding tutorials, and community updates. For a structured path, start with the Understanding Quantum Information & Computation series taught by John Watrous. It's a full university-level course, free, and covers this series' topics in more mathematical depth.

Which lessons match which pages

Older "Coding with Qiskit" videos on the channel were recorded for Qiskit 1.x. Most code still works, but if something fails, compare it with the current documentation.

06 · Free courses and real hardware

Keep going with IBM Quantum Learning

The written version of the Watrous course lives on IBM Quantum Learning, alongside other free courses. One of them, Practical Introduction to Quantum-Safe Cryptography, picks up right where page 09 leaves off.