Quantum Information & Computing

Preface

Will quantum computers truly change the world, or are they just another overhyped trend?

Rather than getting swept up in slogans, “Quantum Information & Computing” is written for readers who want to understand, in a coherent line, the conceptual foundations of quantum computation, concrete algorithms, and real hardware. It is neither a pure formula-heavy textbook nor a light popular-science book, but aims instead for a “semi-textbook level” that balances rigor and accessibility.

Chapter 1 carefully develops the principles of quantum computation using the language of qubits, Hilbert spaces, Bloch spheres, and quantum circuits. From there, we follow the lineage of quantum algorithms—Deutsch–Jozsa, Simon, Shor, Grover—and, through step‑by‑step examples and exercises, see how “quantum parallelism” and “interference” turn into actual computational advantages.

But powerful quantum computers cannot be built with algorithms alone. In Part 3, we start from simple error models such as bit flips and phase flips and work our way up to quantum error‑correcting codes, the stabilizer formalism, and surface codes, building the ideas and techniques of quantum error correction layer by layer. Along the way, the notion of a “logical qubit” emerges naturally, and it becomes clear why tens to hundreds of physical qubits are required to realize just a single logical qubit.

Part 4 then turns to the physical world. Using DiVincenzo’s criteria, coherence times (T_1, T_2), and gate fidelities as guiding metrics, we compare the major hardware candidates: superconducting qubits, trapped ions, neutral atoms, semiconductor spin qubits, and photonic platforms. The goal is not to present an idealized dream machine, but to summarize—based on the best current knowledge—how each platform is actually performing in laboratories and industry, and what trade‑offs they face.

Each chapter follows a common format:

1. Core concepts
   
2. Key formulas and relations
   
3. Intuitive examples
   
4. Exercises
   
5. Solutions

This structure lets readers dive as deeply as they wish into the concepts, while always having examples and problems at hand to check their understanding. For readers comfortable with linear algebra and basic quantum mechanics (spin, state vectors, unitary evolution), this book provides a coherent “map” connecting the language, algorithms, error correction, and hardware of quantum computing.

This is not a book that simply proclaims “quantum computers will change everything,” nor one that dismisses the field as “still too far away.” Instead, it aims to equip physicists, mathematicians, engineers, and interested readers with a solid, quantum‑level framework for making their own informed judgments about the emerging era of quantum information.