You're reading from A Practical Guide to Quantum Computing Hands-on approach to quantum computing with Qiskit

Product type Paperback

Published in Jul 2025

Last Updated in Aug 2025

Publisher Packt

ISBN-13 9781835885949

Length 512 pages

Edition 1st Edition

Languages

Python

Tools

Azure Quantum

Concepts

Quantum Computing

Authors (2):

Elías F. Combarro Fernández-Combarro Álvarez

Samuel González Castillo

View More author details

Table of Contents (29) Chapters

Preface

1. Part 1 One Qubit to Rule Them All: Working with One Qubit FREE CHAPTER

2. Chapter 1 What Is (and What Is Not) a Quantum Computer

3. Chapter 2 Qubits, Gates, and Measurements

4. Chapter 3 Applications and Protocols with One Qubit

5. Chapter 4 Coding One-Qubit Protocols in Qiskit

6. Part 2 Qubit Meets Qubit: Two Qubits and Entanglement

7. Chapter 5 How to Work with Two Qubits

8. Chapter 6 Applications and Protocols with Two Qubits

9. Chapter 7 Coding Two-Qubit Algorithms in Qiskit

10. Part 3 Working with Many Qubits

11. Chapter 8 How to Work with Many Qubits

12. Chapter 9 The Full Power of Quantum Algorithms

13. Chapter 10 Coding with Many Qubits in Qiskit

14. Part 4 The Stars of the Show: Main Quantum Algorithms

15. Chapter 11 Finding the Period and Factoring Numbers

16. Chapter 12 Searching and Counting with a Quantum Computer

17. Chapter 13 Coding Shor and Grover’s Algorithms in Qiskit

18. Part 5 Ad Astra: The Road to Quantum Utility and Advantage

19. Chapter 14 Quantum Error Correction and Fault Tolerance

20. Chapter 15 Experiments for Quantum Advantage

21. Bibliography

22. Solutions

23. Index

Appendix A Mathematical Tools

1. Appendix B The Bra-Ket Notation and Other Foundational Notions

2. Appendix C Measuring the Complexity of Algorithms

3. Appendix D Installing the Tools

4. Appendix E Production Notes

7.1 Working with two qubits in Qiskit

In order to work with two-qubit systems in Qiskit, we need to start by defining a quantum circuit that has a pair of qubits. In quantum computing jargon, these two qubits form what is called a quantum register . In fact, a register is nothing more than a bunch of qubits (or bits, if it is a classical register ) that are grouped together and that we can use for some purpose. In this chapter, we are going to work only with quantum registers of two qubits, but in Chapter 10 we will extend this to registers with an arbitrary number of qubits.

So, how can we define a quantum circuit with a two-qubit register in Qiskit? It couldn’t be easier. We just need to use the following piece of code:

 from qiskit import QuantumCircuit 
 
 circuit = QuantumCircuit (2)

As you surely have noticed, this the exact same invocation that we used, back in Chapter 4, to define one-qubit circuits, but setting the argument in the call to the QuantumCircuit...