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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Comprehend the mysteries—and the amazing potential—of quantum computing
Quantum computing has the promise to be the next huge thing in technology. How do we know that? Look at how much the big players in tech are investing in the technology. Quantum Computing For Dummies preps you for the amazing changes that are coming with the world of computing built on the phenomena of quantum mechanics. Need to know what is it and how does it work? This easy-to-understand book breaks it down and answers your most pressing questions. Get a better understanding of how quantum computing is revolutionizing networking, data management, cryptography, and artificial intelligence in ways that would have previously been unthinkable. With a Dummies guide by your side, you’ll get a primer on the inner workings and practical applications of quantum computers.
- Learn the difference binary and quantum computers
- Discover which industries will be most influenced by quantum computing
- See how quantum improves encryption and enables business
- Take a look at how quantum is applied in big data and AI
For technologists and IT pros interested in getting on board the quantum train—plus anyone who’s quantum-curious—this Dummies guide is a must-have.
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Veröffentlichungsjahr: 2023
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Quantum Computing For Dummies®
Published by: John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030-5774, www.wiley.com
Copyright © 2024 by John Wiley & Sons, Inc., Hoboken, New Jersey
Published simultaneously in Canada
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Library of Congress Control Number: 2023942826
ISBN 978-1-119-93390-8 (pbk); ISBN 978-1-119-93391-5 (ebk); ISBN 978-1-119-93392-2 (ebk)
Quantum Computing For Dummies®
To view this book's Cheat Sheet, simply go to www.dummies.com and search for “Quantum Computing For Dummies Cheat Sheet” in the Search box.
Table of Contents
Cover
Title Page
Copyright
Introduction
About This Book
Foolish Assumptions
Icons Used in This Book
Beyond the Book
Where to Go from Here
Part 1: The Power of Quantum Computing
Chapter 1: Quantum Computing Boot Camp
Understanding Why Quantum Computing Is So Strange
Grasping the Power of Quantum Computing
Doing the Math for the Power of Quantum Computing
Examining What Quantum Computing Will Do for People
Describing Different Types of Quantum Computing
Addressing What’s Stopping Us
Chapter 2: Looking Back to Early and Classical Computing
Understanding Why Classical Computers Are Not Going Away
Looking Back to the Prehistory of Computers
Tracking the Emergence of Classical Computing
Joining Classical Computing and Quantum Computing
Chapter 3: Examining the Roots of Quantum Computing
Identifying the Keys to Quantum Mechanics
Identifying the Effect of Uncertainty
Summarizing the History of Quantum Mechanics
Chapter 4: Introducing Quantum Technology 1.0
Finding Lasers at the Cutting Edge
Studying Quantum Mechanics After 1930
Speeding the Race for Solar Cells (1890s)
Eyeing Electron Microscopes (1931, 1965, and 1981)
Optimizing the Transistor (1947)
Telling Time with Atomic Clocks (1955)
Heating Up Masers and Lasers (1953 and 1960)
Scanning for NMR and MRI Devices (1977)
Assessing the Effects of Quantum Technology 1.0
Chapter 5: Unveiling Quantum Computing
Nailing Together a Framework for Quantum Computing
Theorizing in the 1960s and 1970s
Laying the Groundwork in the 1980s
Breaking through in the 1990s with Algorithms and Hardware
Starting Today’s Quantum Computing Race
Chapter 6: Quantum Computing Accelerates
Pushing Technical Progress Forward, 2000–2010
Investing More Resources from 2010-2015
Bending the Arc of Progress Upward, 2016 to Today
Finding Out What’s Still Needed for Quantum Computing
Part 2: Quantum Computing Options
Chapter 7: Choosing Between Classical and Quantum Computing
Identifying Limitations in Classical Computing
Finding What’s Right with Quantum Computing
Chapter 8: Getting Started with Quantum Computing
Identifying Five Classes of Solutions
Dancing to That Algorithm
Deciding Whether to Start Now
Getting Your Organization Involved
Considering Quantum-Inspired Solutions
Chapter 9: It's All about the Stack
Analyzing the Stack
Considering the Annealing Alternative
Choosing a Type of Quantum Computer
Chapter 10: Racing for the Perfect Qubit
Identifying Three Levels of Qubit Achievement
Winning the Race for Focused Quantum Advantage
Visiting the Qubit Zoo
Mapping Out the Modalities Landscape
Figuring Out What’s Next
Chapter 11: Choosing a Qubit Type
Telling the Players Apart with a Scorecard
Choosing a Strategy for Quantum Computing
Part 3: Getting Entangled with Quantum Computing
Chapter 12: Programming a Quantum Computer
Figuring Out What We Are Doing
Figuring Out How to Do It
Getting Down to the BASICs
Writing the Requirements for a Quantum Program
Thinking Like a Developer
Setting Up a Development Environment
Finding Where to Get Your Quantum On
Singing QAOA-ooooo
Breaking Down a Quantum Algorithm
Asking Where Do We Go Now?
Chapter 13: Quantum Computing Applications
Thinking in Triplicate
Cracking Cryptography with Quantum
Finding Waldo in a Sea of Striped Hats
Grabbing That Cash
Insuring That Quantum Makes Its Mark
Making the World Go Round with Logistics
Dreaming of Machines Learning
Searching for the New Oil in Quantum
Making Materialism Matter
Simulating Our Way to Better Health
Finding New Pharmaceuticals
Forecasting Future Fog
Chapter 14: Quantum Computing Algorithms
Mapping Quantum Computing Algorithms to Applications
Understanding the Basics of Quantum Algorithms
Visiting the Quantum Zoo
Finding New Kinds of Time
Starting with the Deutsch-Jozsa Algorithm
Making Shor Quantum Computing Will Be Big
Searching with Grover
Using the Quantum Phase Estimation Algorithm
Applying Simon's Algorithm
Implementing the Quantum Fourier Transform (QFT) Algorithm
Stepping into Vaidman's Quantum Zeno Effect
Getting Linear with the HHL Algorithm
Solving and Simulating with QAOA
Getting Grounded with VQE
Assessing Additional Algorithms
Identifying What’s Ahead
Chapter 15: Cloud Access Options
Exploring the Major Types of Options
Noting the Importance of Amazon Braket
Counting on Azure Quantum
Investigating Google Quantum AI
Opening Quantum Computer Vendor’s Portals
Unlocking Quantum Potential with Strangeworks
Chapter 16: Educational Resources
Connecting with Online Classes
Trying Tutorials and Documentation
Skipping through Unstructured Study
Getting into Interaction and Fun
Part 4: The Part of Tens
Chapter 17: Ten Myths Surrounding Quantum Computing
Myth 1: Quantum Computing Won't Be Commercially Available for 10–15 Years
Myth 2: A Qubit Can Be a 0 and a 1 at the Same Time
Myth 3: Quantum Computers Will Replace Classical Computers
Myth 4: Only a Physicist Can Program Quantum Computers
Myth 5: Quantum Computers Will Soon Solve All Classical Computer Problems
Myth 6: We Should All “Shut Up and Calculate”
Myth 7: Soon There Will Be Only a Small Number of Quantum Hardware Companies
Myth 8: Quantum Companies Have All the Talent They Need to Grow the Industry
Myth 9: Quantum Computing Will Destroy Data Encryption
Myth 10: Quantum-Safe Cryptography Provides Complete Data Security
Chapter 18: Ten Tech Questions Answered
Will Quantum Technology Find Its Way into a Consumer Product?
Is the Quantum Realm Real? Will Ant-Man Save Our World?
How Do You Explain Quantum Computing to a Dummy?
Where Is the Quantum Computing Field Going?
When Will Quantum Computing Become Commercially Practical?
What Is the Coolest Application of Quantum Computing?
Where Will Quantum Computing Be the Most Disruptive?
How Long Until Shor's Algorithm Breaks RSA?
How Can You Use Quantum Computing in Manufacturing?
Where Is the Overlap Between Quantum Computing and AI/ML?
Chapter 19: Ten Business Questions Answered
How Can I Evaluate the Market for a New Company, Product, or Service?
How Do I Evaluate My Employer’s Need to Be an Early Adopter (or Not)?
What Roles and Jobs Are Needed in the Current Stage of Development?
What Background Is Needed to Learn Quantum Computer Coding?
What Advice Can You Give to First-Timers?
What University Programs Would You Recommend?
Who Is the Current Leading Developer of Quantum Computing?
What Should I Do if I Have an Idea for a Startup?
What Habits Have Helped You in Your Career?
What Are Your Biggest Lessons Learned?
Chapter 20: Ten University Research Programs
University of Oxford, UK
University of California, Berkeley
Stanford University
Cal Tech
Massachusetts Institute of Technology
Harvard University
University of Chicago
University of Maryland
University of Waterloo
University of New South Wales, Sydney
Index
About the Authors
Advertisement Page
Connect with Dummies
End User License Agreement
List of Tables
Chapter 7
TABLE 7-1 Proof-of-Concept Implementations of Quantum Algorithms
Chapter 9
TABLE 9-1 Comparing Quantum Annealers and Universal Quantum Computers
Chapter 14
TABLE 14-1: Some Quantum Computing Algorithms Are Useful across a Range of Appli...
Chapter 15
TABLE 15-1 Public Cloud Providers and Quantum Computer Manufacturers
List of Illustrations
Chapter 1
FIGURE 1-1: A quantum computing processor from IBM.
FIGURE 1-2: IBM’s quantum computing roadmap shows past and anticipated growth i...
FIGURE 1-3: Entangled qubits influence each other.
Chapter 2
FIGURE 2-1: The abacus is amazingly fast and accurate in the hands of an experi...
FIGURE 2-2: The Antikythera is still slowly yielding its secrets.
FIGURE 2-3: Slide rules once ruled, from artillery ranges to Cape Kennedy to lu...
FIGURE 2-4: A tabulating machine and its operator add results from the 1950 cen...
FIGURE 2-5: A World War II German Enigma cryptographic machine.
FIGURE 2-6: Architecture of a typical classical computer.
FIGURE 2-7: The Intel 80486, an important microprocessor.
Chapter 3
FIGURE 3-1: Electron orbitals are rendered as shapes that show the most likely ...
FIGURE 3-2: A superconducting maglev train running on the first operational lin...
FIGURE 3-3: Galileo’s
Dialogue
presented his heliocentric view of the planets.
FIGURE 3-4: The fifth Solvay conference included most of the key contributors t...
Chapter 4
FIGURE 4-1: A medical-grade laser.
FIGURE 4-2: Advanced solar power cells energize space exploration.
FIGURE 4-3: A wafer of microprocessors.
FIGURE 4-4: A strontium ion optical clock.
FIGURE 4-5: A laser supercooling atoms.
FIGURE 4-6: Sir Peter Mansfield with an original MRI machine.
Chapter 5
FIGURE 5-1: Augusta Ada King, Countess of Lovelace.
FIGURE 5-2: Richard Feynman opens students’ minds in a 1959 lecture.
FIGURE 5-3: A CNOT gate, vital to gate-based quantum computing.
FIGURE 5-4: Quantum communication puts entanglement to work.
FIGURE 5-5: The US Department of Defense has big ideas for quantum technologies...
FIGURE 5-6: Grover’s algorithm finds needles in haystacks faster.
FIGURE 5-7: The first working 2-qubit computer was created in 1998.
Chapter 6
FIGURE 6-1: The Institute for Quantum Computing at the University of Waterloo.
FIGURE 6-2: Entanglement for quantum communications reached space in 2017.
FIGURE 6-3: John Martinis, upper right, worked at NIST-Boulder in the 1990s.
Chapter 7
FIGURE 7-1: If you’re 60 or younger, microprocessor speeds have doubled every y...
FIGURE 7-2: Cloud provider revenues — which also means cloud user costs — are r...
FIGURE 7-3: The number of calculations for exponential-type runtimes grows very...
FIGURE 7-4: Fluid dynamics are crucial in airplane design.
Chapter 8
FIGURE 8-1: Expected usefulness of quantum computing solutions over time.
FIGURE 8-2: Factorization on classical computers versus a future quantum comput...
FIGURE 8-3: The challenge to internet security posed by quantum technology is r...
FIGURE 8-4: Identifying tactical and strategic opportunities for your organizat...
FIGURE 8-5: Future actions to consider after evaluating a product presentation.
Chapter 9
FIGURE 9-1: The layers that make up a quantum computing system.
FIGURE 9-2: E pluribus unum (out of many, one) — good for a country but hard on...
FIGURE 9-3: A D-Wave computer used to solve an optimization problem.
FIGURE 9-4: A representation of the structure of annealed iron.
FIGURE 9-5: Finding the highest maximum is not always easy.
Chapter 10
FIGURE 10-1:
Space Race
is one of many histories of the US versus USSR race to ...
FIGURE 10-2: whurley’s talk on QuantumanAI describes how quantum computing and ...
FIGURE 10-3: Comparing modalities for major qubit types.
FIGURE 10-4: A rough idea of scale and fidelity for current quantum computing m...
Chapter 11
FIGURE 11-1: Quantum computing vendors by modality.
FIGURE 11-2: Ionized atoms are easily controlled by magnets in trapped ion quan...
FIGURE 11-3: Superconducting loops are at the core of transmon qubits.
FIGURE 11-4: Photons can be used for qubits in a variety of ways.
FIGURE 11-5: NMR qubits were vital in bringing quantum computing to life in the...
Chapter 12
FIGURE 12-1: A Bloch sphere.
FIGURE 12-2: Selected quantum computing logic gates.
FIGURE 12-3: An example of a quantum circuit.
FIGURE 12-4: The Strangeworks product catalog.
FIGURE 12-5: The Strangeworks QAOA service makes simulation more approachable.
FIGURE 12-6: This screen is where you replace your API key.
FIGURE 12-7: The completed job appears in the Strangeworks portal.
Chapter 13
FIGURE 13-1: Quantum-inspired computing is being used by Fujitsu and Toyota to ...
FIGURE 13-2: Quantum computing and machine learning are being used to create gl...
Chapter 14
FIGURE 14-1: The family tree of algorithms includes ready-to-use algorithms and...
FIGURE 14-2: The Quantum Algorithm Zoo is a rich resource for work in quantum c...
FIGURE 14-3: Time still has meaning in quantum computing — just a different mea...
FIGURE 14-4: The quantum phase estimation algorithm estimates the phase shifts ...
FIGURE 14-5: The classical fast Fourier transform decomposes a signal into its ...
FIGURE 14-6: Zeno’s paradox asserts the impossibility of ever accomplishing any...
Chapter 15
FIGURE 15-1: Amazon Braket console.
FIGURE 15-2: A summary of Microsoft’s Azure Quantum offering.
FIGURE 15-3: Using a notebook to run a job in Microsoft’s Azure Quantum service...
FIGURE 15-4: Google has developed Cirq, a Python software library for quantum c...
FIGURE 15-5: The IBM Quantum Composer is a no-code processing tool that emits P...
FIGURE 15-6: The Strangeworks portal delivers quantum computing information at ...
FIGURE 15-7: The Strangeworks product catalog gives you access to a wide range ...
FIGURE 15-8: The Strangeworks “long list” of compute providers is comprehensive...
FIGURE 15-9: IBM Quantum is one of the compute providers available in the Stran...
FIGURE 15-10: You can see jobs waiting to run on your chosen resource.
FIGURE 15-11: You can see jobs waiting to run on your chosen resource.
FIGURE 15-12: Click to see the details of each job running in your workspace.
FIGURE 15-13: Strangeworks managed applications run on multiple providers.
FIGURE 15-14: You can click into details for each Strangeworks managed applicat...
Chapter 16
FIGURE 16-1: Quantum superposition, as rendered by the MIT Quantum Information ...
FIGURE 16-2: Quantum Quest provides a learning opportunity designed for high-sc...
FIGURE 16-3: Strawberry Fields doesn’t take forever to work through.
FIGURE 16-4: A mutually orthogonal interaction between Bob and Alice is describ...
FIGURE 16-5: The Quantum Computing Playground makes Shor you learn something ab...
FIGURE 16-6: Quirk may have its quirks, but so does quantum computing.
Guide
Cover
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Copyright
Table of Contents
Begin Reading
Index
About the Authors
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Introduction
Quantum computing is a lot like the sulfur-spewing hydrothermal vents at the bottom of the Mariana Trench: It’s both hot and deep. (The vents in the Mariana Trench are also surrounded by strange life forms, which implies something not very nice about us, your authors.)
Quantum computing is hot because progress, activity, interest, and investment are all continuing to grow to unprecedented levels. And it’s hot also because popular culture says so. Movies like the 2023 Oscar winner, Everything Everywhere All at Once, and the Netflix series 3 Body Problem make quantum mechanics — the technology that underlies quantum computing — lively, interesting, and even funny.
And why is quantum computing deep? Because it directly applies quantum mechanics to some of the biggest problems that humanity faces today, such as drug discovery, lifespan enhancement, and climate change. And the workings of the quantum world challenge our understanding, sometimes even our grasp on, reality.
Entanglement is a core principle of quantum computing, and the 2022 Nobel Prize in Physics was awarded for work on entanglement. Yet no less a figure than Albert Einstein called entanglement “spooky action at a distance.” Quantum computing depends on this “spooky action” and other quantum mechanical principles to deliver incredible results.
All this makes the two of us very happy to bring you Quantum Computing For Dummies. We hope this book will direct your attention toward the big picture where needed — and also show you when it’s time to, as the expression says, “shut up and calculate.” Or program. Or make hard-nosed business decisions about where to put your time, energy, and money.
About This Book
Quantum Computing For Dummies provides a clear and concise introduction to the terminology, technology, and techniques you need to use quantum computing to get a job, make business decisions, invest, or just introduce yourself to this fascinating new technology.
With this book as your guide, you’ll learn about
The core principles of quantum mechanics
How quantum mechanics relates to quantum computing
Where the technology is today and how it relates to your business and career
How quantum-inspired computing, a transitional technology, is being used to solve advanced problems on today’s computers
The difference between quantum annealing, another transitional technology, and gate-based quantum computing — the most complete expression of quantum computing technology
Which gate-based quantum computing modality to use, based on nearly a dozen types of qubits
More than a dozen quantum algorithms that might help to solve problems that your business faces today
Identifying which kind of speedup quantum computing might offer for the problems that affect your business today
The steps needed to make your business ready for — or a leader in — quantum computing
Choosing a cloud provider to help you get started with the technology, often for free
Online courses on how to program quantum computers
Signing onto a live portal and starting your own quantum computer programming journey
Resources, online and offline, to further your knowledge or quantum computing
University programs to help you take the next step toward a quantum computing career
You’re going to be seeing news stories about progress in quantum computing, and you may find yourself discussing the technology with friends or at work. You may even consider taking your career in this new direction. All of which leads to a simple question: What can you actually do about quantum computing?
This book answers that question. It enables you to relate the computers we all use today — called classical computers — to this strange new beast, quantum computing. It shows you what you can do with quantum computers today, and what you will likely be able to do in the future. And it punctures many myths about quantum computing.
The book then goes on to show you how to get started in quantum computing at work, whether that’s programming a quantum computing or using quantum computing in your business. And it helps you understand the technology trends so you can keep an eye on new opportunities as quantum computing moves forward.
Quantum computing is quite different than the classical computers you’re accustomed to. This book can help you decide when to use each type of computing, now and in the future.
You can learn bits and pieces about quantum computing by reading news stories and poking around online. But with this book, you get a complete picture. You can decide whether you and your business need to get started with quantum computing today — and if so, you can roll up your sleeves and get to work.
Foolish Assumptions
Quantum Computing For Dummies is written for beginners, which means you might not even know for sure what quantum computing is. We don’t assume that you know physics or mathematics beyond what common sense tells you. And we don’t assume that you've programmed a computer (of any kind) before.
However, we do assume that you
Have used a computer or a smartphone or both
Have access to the internet so you can do further research on new topics
Are interested in what quantum computing can do for your career, your business, or the world
Icons Used in This Book
If you’ve read other Dummies books, you know that they use icons in the margin to call attention to particularly important or useful ideas in the text. In this book, we use four of these icons.
The tip icon highlights expert shortcuts or simple ideas that can make life in the quantum computing field easier for you.
You could say that this whole book is technical stuff, but this icon highlights information that’s particularly technical. You can re-read information highlighted with this information if you want to go deep, or skip it if you don’t want to know all the details. It’s entirely up to you!
While we would like to think that every word in this book is unforgettable, we’d like you to carry some information to other areas of the book. We highlight these points so you can quickly find important takeaways that matter quite a bit in helping you get up to speed with quantum computing.
Just as you would do if you were driving a car, slow down when you see a warning sign. It highlights an area where it’s easy to make a mistake or develop a misunderstanding.
Beyond the Book
To get to the web page for this book, go to www.dummies.com and type Quantum Computing For Dummies in the Search box. The web page includes the book's cheat sheet, which defines basic terms, describes the different types of quantum computers, lists the most-used types of qubits, and links to some of the online classes about quantum computing. You’ll also find bonus chapters with tech and business information.
Occasionally, the publishers provide updates to Dummies books. If this book has technical updates, you can find them here as well.
To see the free programming introduction mentioned in Chapter 12, go to www.dummies.com/go/quantumcomputingfd.
One of the book’s authors, William Hurley (known as whurley), maintains a personal website with information about quantum computing and other topics of interest. You can visit it at www.whurley.com. whurley is also CEO of Strangeworks, a quantum computing company. You can visit Strangeworks at www.strangeworks.com.
Where to Go from Here
Part 1 introduces you to quantum computing and the most closely related technologies, quantum mechanics and classical computing (the computers you use today). Part 2 is a deep dive into the different ways you can do quantum computing today and the different qubit types used in gate-based quantum computing, the most advanced (and, so far, least developed) form of the technology. Part 3 is quite practical, if we can use that word to describe an almost mystical technology; it introduces you to quantum computing algorithms, quantum computer programming, and educational resources for learning more. And Part 4 is the famous Dummies “Part of Tens”; it gives you lists of key points mentioned in the book, covering both technical and business information.
You can read this book in any way you’d like. If you go straight from beginning to end, the book will take you on a journey from the basics of quantum computing and classical computing to in-depth knowledge of technical topics such as qubits and quantum computing algorithms. It will then show you how to access and program quantum computers and give you a variety of ways to move yourself, your career, and your organization forward with the technology.
At the same time, we understand that you might want to pop in and out of the book. You may want to go deep on topics that interest you and skim other sections. You can look at the topics that interest you in the order that we have them arranged in the book; in your own order, based on your own interests; or in no specific order at all. The book is full of cross-references and signposts to help you find all the information you need.
Part 1
The Power of Quantum Computing
IN THIS PART …
Get a big-picture overview of quantum computing hardware and software and the current state of progress in the field.
Learn about early computing and classical computing, the approach that describes the many types of computers, from PCs to smartphones to Roombas, that people use in daily life today.
Investigate the roots of quantum computing, made up of discoveries in quantum mechanics which burst onto the scene in the early 1900s, led by figures such as Albert Einstein and Neils Bohr.
Find out how quantum mechanics was first used to develop early quantum computing technologies such as X-ray machines, television, and laser beams.
Come along as we follow quantum mechanics technology into the early days of quantum computing, including the first quantum computing algorithms and the first qubits.
Observe the emergence of quantum computing in the last few years as research and development, interest, and venture capital investment all rise quickly.
Chapter 1
Quantum Computing Boot Camp
IN THIS CHAPTER
Adding strangeness to our agenda
Calculating the power of quantum computing
Identifying quantum computing’s advantages
Taking stock of quantum computer types
Overcoming barriers to new capabilities
Picture flipping a coin in the air. As it’s spinning, is it showing heads or tails? Well, you can't know the answer while the coin is spinning. Only when the coin lands and settles down does it display a definite result.
The uncertainty you see while the coin is spinning is like the uncertainty we capture and use in quantum computing. We put many processing elements — qubits — into a state of uncertainty. Then we program the qubits, run the program, and capture the results — just like when the coin lands.
Quantum computing is different from the fixed 0s and 1s, bits and bytes, used in today’s devices. Quantum computing is based on quantum mechanics, a branch of physics that can be hard to comprehend. But the way in which quantum computing deals effectively with large degrees of uncertainty feels like the way we make many of the decisions we encounter in daily life.
Quantum computing is complementary to classical computing, the kind of computing we use today, not a replacement for it. By working with uncertainty, we can take on some of the biggest, most complex problems that humanity faces, in a new and powerful way. Quantum computing will solve problems for which today’s computing falls short — problems in areas such as modeling the climate, drug discovery, financial optimization, and whether or not it’s a good morning to launch a rocket.
Quantum computing is just getting started; many advanced quantum computers run only for a fraction of a second at a time. However, steady progress is being made. Even now, at this early stage, quantum computing is inspiring us to, as a sage once said, “think different” about the way we use existing computing capabilities. In this chapter, we introduce the power and potential of quantum computing.
This chapter presents many terms and concepts that may be unfamiliar to you. Don’t worry; we explain them all in later chapters. (For instance, Chapter 3 describes quantum mechanics and how quantum computing depends on it.) Think of this chapter as boot camp for the new, quantum-computing-savvy you who will emerge after reading this book.
Understanding Why Quantum Computing Is So Strange
Quantum computers have a sense of strangeness about them, almost a mystical aura. (The 2022 movie, Dr. Strange in the Multiverse of Madness, captures some of the feeling that people have about quantum mechanics in general.) Why is this?
There are two main reasons. The first reason is people’s fundamental misunderstanding of the nature of matter, which quantum mechanics explains. The second is the incredible power that quantum computing, when mature, is expected to deliver to humanity.
How does quantum mechanics (described in Chapter 3) change people’s view of the world? The world we live in, where rocks fall down and rockets go up, seems to be dominated by solid matter, with energy as a force that acts on matter at various times. Yet matter can simply be seen as congealed energy.
Most of the mass of the protons and neutrons inside the nucleus of an atom, for instance, is simply a bookkeeper’s description of the tremendously powerful energetic fields that keep these particles in place. One of the most important kinds of particles in quantum computing, photons, have no mass at all; they are made up of pure energy.
And it was Einstein himself who told us that matter and energy are equivalent, with his famous equation, E=mc2. To translate: The energy contained in solid matter equals its mass times the speed of light squared.
The speed of light is a very large number — 300,000 km/second, or 186,000 miles/second. Squaring the speed of light yields a far larger number. Plug this very large number into Einstein’s famous equation and you'll see that there is a lot of energy in even small amounts of matter, as demonstrated by nuclear power plants and nuclear weapons.
The point is that, in quantum mechanics, matter is relatively unimportant; particles act more as bundles of energy. And quantum computing takes advantage of the exotic properties of these particles — ionized atoms, photons, superconducting metals, and other matter that demonstrates quantum mechanical behavior.
The second reason that quantum computers get such a strong emotional reaction is the tremendous power of quantum computing. The best of today’s early-stage quantum computers are not much more powerful, if at all, than a mainstream supercomputer. But future quantum computers are expected to deliver tremendous speedups.
Over the next decade or two, we expect quantum computers to become hundreds, thousands, even millions of times faster than today’s computers for the problems at which they excel. People can’t really predict, nor even imagine, what it’s going to be like to have that kind of computing power available for some of the most important challenges facing humanity, as we describe in Chapters 13 and 14. That future is very exciting, yes. But it’s also a bit, as Einstein described quantum mechanics, “spooky.”
Grasping the Power of Quantum Computing
To help you get started in understanding quantum computing, here are five big ideas to get your head around:
Qubits:
Qubits
are the quantum computing version of bits — the 0s and 1s at the core of classical computing. They have quantum mechanical properties. Qubits are where all the magic happens in quantum computing.
Superposition:
While bits are limited to 0 or 1, a qubit can hold an undefined value that is neither 0 nor 1 until the qubit is measured. The capability to hold multiple values at once is called
superposition.
Entanglement:
In classical computing, bits are carefully separated from each other so that the value of one does not affect others. But qubits can be entangled with each other. When changes to one particle cause instantaneous changes to another, and when measuring a value for one particle tells you the corresponding value for another, the particles are
entangled
.
Tunneling:
A quantum mechanical particle can instantaneously move from one place to another, even if there’s a barrier in between. (Quantum computing uses this capability to bypass barriers to the best possible solution.) This behavior is referred to as
tunneling
.
Coherence:
A quantum particle, such as an electron, that is free of outside disturbance is
coherent.
Only coherent particles can exhibit superposition and entanglement.
How are these terms related? Here’s an example: A good qubit is relatively easy to place into a state of coherence and maintain in a state of coherence, so it can exhibit superposition and entanglement, and therefore can tunnel. (The search for “good qubits” is the subject of a lot of work and controversy today. We describe this topic in more detail in Chapters 10 and 11.)
These five terms are at the heart of the promise of quantum computing and are involved in many of the challenges that make quantum computing difficult to fully implement. In this section, we describe each of these crucial concepts.
Classical computing describes the computers we use every day, which includes not only laptop and desktop computers but also smartphones, web servers, supercomputers, and many other kinds of devices. The term classical computing is used because classical computers use classical mechanics, the cause-and-effect rules of the road that we see and use in our daily lives, for information processing. Quantum computing uses quantum mechanics — which is very different, very interesting, and very powerful indeed — for information processing. We mention some quantum mechanical principles in this chapter and go into more detail in Chapter 2.
Introducing Puff, the magic — qubit?
Bits power classical computing — the laptops, servers, smartphones, and supercomputers that we use today. Bit is short for binary digit, where digit specifies a single numeral and binary means the numeral can have only one of two values: 0 or 1 — just like the results of a coin flip.
In a computer, bits are stored in tiny, cheap electromechanical devices that reliably take in, hold, and return either a 0 or a 1 — at least until the power is turned off. Because a single bit doesn’t tell you much, bits are packaged into eight-bit bytes, with a single byte able to hold 256 values. (28 — all possible combinations of 8 binary digits — equals 256.)
A qubit is a complex device that has, at its core, matter in a quantum mechanical state (such as a photon, an atom, or a tiny piece of superconducting metal). The qubit includes a container of some kind, such as a strong magnetic field, that keeps the matter from interacting with its environment.
A qubit is much more complex and much more powerful than a bit. But qubits today are not very reliable, for two reasons:
They’re subject to errors introduced by noise in the environment around them. A result of 0 can be accidentally flipped to a result of 1, or vice versa, and there’s no easy way to know that an error has occurred.
It’s hard to keep qubits coherent, that is, capable of superposition, entanglement, and tunneling.
The situation with qubits today is somewhat like the old joke about a bad restaurant: “The food is terrible — and the portions are so small!” With qubits, the error rates are high and the coherence period is short. But despite these problems, quantum computers do deliver valuable and interesting results while up and running.
In quantum computers, qubits are much more complex and far more expensive than bits. Nor are they as easy to manage — but they are far more powerful.
Figure 1-1 shows a quantum computing module from IBM, suspended at the bottom of a cooling infrastructure that keeps the superconducting qubits at a temperature near absolute zero.
Until it's measured, each qubit can represent an infinite range of values between 0 and 1. How does the qubit hold all these values? At the core of the qubit is a quantum particle — a tiny piece of reality in the form of a photon, an electron, an ionized atom, or an artificial atom formed using a superconducting metal.
For quantum computing, the quantum particle at the core of the qubit must be kept in a coherent state — uncontrolled, like the flipped coin while it’s spinning in the air. In a coherent state, we don’t know whether the value of the qubit at a given moment is 0 or 1. When we measure the state of the qubit, the calculation we want to make is performed, and the qubit returns 0 or 1 as a result.
Flickr/Lars Plougmann
FIGURE 1-1: A quantum computing processor from IBM.
Much of the power of qubits comes from the fact that they behave in a probabilistic manner; a given qubit, running the same calculation multiple times without errors, may produce a 0 on some runs and a 1 on another. The final result consists of the number of times each qubit returns a 0 or a 1. So the result of most quantum calculations is a set of probabilities rather than a single number.
Qubits are hard to create and hard to maintain in a state of coherence; they also tend to interfere with nearby qubits in an uncontrolled fashion. Taming qubits is one of the biggest challenges to overcome in creating useful quantum computers.
A popular approach to building quantum computers involves the use of superconducting qubits, which must be kept at a temperature very close to absolute zero to minimize interference due to heat and, in many cases, to maintain superconductivity.
Classical computers are designed to work at room temperature, but they tend to generate heat and to stop working properly as the temperature rises. The need to dissipate heat prevents device makers from packing components as tightly as they would like without resorting to expensive and clumsy solutions such as water-cooling or refrigerating the components.
In quantum computing, each additional qubit adds exponentially to the power of the computer. But because qubits tend to interfere with each other, adding more is difficult.
IBM, a leader in quantum computing, has published a roadmap showing past and future increases in the number of qubits that power its current and upcoming quantum computers. A simplified version of the roadmap is shown in Figure 1-2. You can find a link to the current version of the roadmap at https://research.ibm.com/blog/ibm-quantum-roadmap-2025.
FIGURE 1-2: IBM’s quantum computing roadmap shows past and anticipated growth in the number of qubits available.
Superposition, the first quantum superpower
The state of possibility that's available to qubits is called superposition, where super means many and position means possibilities. A traditional bit can be either 0 or 1. A qubit in a state of superposition does not have a defined value because it holds many potential values at the same time. But when we measure a qubit, we just get 0 or 1 back — whichever value the qubit’s energetic wave function collapsed to when it was measured.
Superposition is the first of two major pillars underpinning the power of quantum computing. The other, entanglement, is described in the next section.
In Chapter 3, we describe how the creators of quantum mechanics discovered superposition and other quantum principles during an extraordinary period of scientific creativity between about 1900 and 1930. (This period also saw the disaster of World War I and the beginning of the Great Depression.)
EXPLAINING LIFE, THE MULTIVERSE, AND EVERYTHING
Quantum computing depends on the laws of quantum mechanics, described at a basic level in Chapter 3. Quantum mechanical principles are vital to the operation of quantum computers.
One way of understanding how quantum mechanics works is that each possible state of a quantum mechanical object becomes true — in a new parallel universe that comes into existence to contain that possibility. This way of looking at reality is the basis of recent movies such as Everything Everywhere All at Once and Quantumania. But there’s ongoing controversy as to whether multiple universes are real.
We don’t need to get caught up in these debates as we do our daily work in quantum computing; we can, as the saying goes, “shut up and calculate.” But these seemingly wild ideas can help us understand just how strange and wonderful the quantum world is. They can inspire us in our daily work, and they may lead to seemingly science-fictional achievements such as time travel, teleportation, and faster than light travel — for information, at least, if not for objects or people.
Welcoming foreign entanglements
George Washington once warned Americans to avoid foreign entanglements. But with qubits, we welcome entanglement as an additional, powerful tool in our quantum computing toolkit.
Entanglement is a kind of connection between two or more quantum particles. For instance, quantum particles have a property called spin, which we can measure as either down or up (0 or 1). If two quantum particles are entangled and one of them is measured as having an up spin, we know without measuring that the other entangled particle will have a down spin. And if we influence the spin of the first quantum particle so that it changes to up when it is measured, we know without measuring that the other quantum particle will change to down.
Figure 1-3 shows the connection between two entangled qubits, which have opposing spins. Measuring the spin of one tells you that the spin of the other is the opposite; changing the spin of one qubit in one direction will change the spin of the other in the opposite direction.
As mentioned, entanglement is the second pillar supporting the power of quantum computing. With entangled qubits, influencing a single qubit can have a knock-on effect on many others.
FIGURE 1-3: Entangled qubits influence each other.
Entanglement and superposition work together. When an entangled qubit is in a state of superposition, each of its entangled connections is also in a state of superposition. These cascading uncertainties exponentially increase the potential power of quantum computers.
To program and run calculations on a quantum computer, the potentiality of the entangled qubits must be maintained by keeping them coherent and free from noise. We then measure the qubits (which causes them to decohere) and record the results, a 0 or 1 for each qubit.
Quantum communications is made possible by using entangled qubits for communication between distant locations. We explain this in more depth in Chapter 3.
Enabling quantum computing with coherence
Qubits can be used for quantum computing only when they’re kept in a state of coherence, free of interaction with their environment. To do quantum computing, qubits need to follow the rules of quantum mechanics (as explained in Chapter 2), and these rules apply to only coherent qubits.
Quantum particles zipping around the universe — photons emitted by the sun, for example — are in a state of coherence. What causes them to decohere? Any interaction with excessive interference (such as vibration or a strong magnetic field), a solid object, or a measuring device.
Keeping qubits coherent is hard. Heat decoheres them, so qubits are kept cold. So do vibration (think of a truck going by on a road) and any collision with their environment. To prevent such collisions, qubits often use strong magnetic fields or targeted laser beams to prevent the quantum particles inside them from colliding with their physical containers.
BLOWING PAST C
Albert Einstein wears two hats in the history of quantum mechanics — and the two hats don’t fit comfortably on a single head.
One hat comes from Einstein’s discovery of relativity, published in 1905. Relativity says that speed in this universe depends on your motion relative to other observers, but that the speed of light — about 186,000 miles per second, or 300,000 kilometers per second — is always the same for all observers. This universal speed limit is called locality.
The other hat comes from Einstein’s discovery of the photon, also in 1905. (This discovery, not relativity, is the source of Einstein’s sole Nobel Prize.) The discovery of the photon is fundamental to quantum mechanics.
Einstein’s problem is that quantum mechanics later asserted that quantum particles, such as photons, can be entangled with each other, so that reading the spin (for example) of one photon tells you the spin of the other. And this relationship is instantly true, without regard to the speed of light. Physicists call this an assertion of nonlocality, which is supposed to be forbidden by relativity.
Einstein hated this, calling it “spooky action at a distance.” He and his colleagues spent a great deal of effort trying to disprove it, even as Einstein continued to make breakthrough quantum discoveries, such as the identification of Bose-Einstein condensates, which are superconducting gases that can be used to create qubits.
Today’s mainstream computers are subject to classical mechanics and limited by the speed of light. Quantum computers depend on quantum mechanics and, in their use of entanglement, are not limited by light speed.
The Nobel Prize for Physics in 2022 was awarded to physicists who showed that entanglement is real. So researchers in quantum computing who depend on entanglement can say, after Galileo: “And yet it computes.” (Galileo, on trial for asserting — correctly, as it turned out — that the earth is not at the center of the universe, is famously said to have whispered: “And yet it moves.”)
Decoherence is not the only disaster that can affect qubits. Temperature changes, vibration, or physical interaction may change the value of a qubit in an uncontrolled manner without causing it to decohere. This noise causes errors in the results of quantum computations. Minimizing noise and detecting errors are two of the biggest challenges facing quantum computers.
To manipulate each qubit — to program it, for instance, for quantum computing — the qubit must be controlled in such a way as to adjust its value without causing it to decohere. Magnetic fields and laser beams are among the means used to manipulate qubits without causing decoherence.
When we measure the value of a qubit, two things happen:
The qubit decoheres, becoming subject to the rules of classical mechanics.
The qubit’s value collapses from somewhere between 0 and 1, inclusive, to either 0 or 1.
The qubit must be reinitialized — returned to coherence — before it can be used again for computing.
Some argue that the potential of quantum computers is very limited — that the level of coherence needed for quantum computers to achieve useful results is impossible, in theory and in fact. In the extreme version of this argument, leaders in quantum computing are accused of deliberately committing fraud, which would mean that the entire field is a massive conspiracy. Only further work will show the limits to quantum computing, if any, but the fraud allegations are just a conspiracy theory.
Doing the Math for the Power of Quantum Computing
It’s challenging to fully grasp the potential power of quantum computing compared to classical computing because that power is based on quantum mechanical principles. But we can sum it up in just a bit of math.
Because the bits in classical computing can hold only one of two values — a 0 or a 1 — at the same time, the number of states that a classical computer can hold is represented by the number of bits, n, to the power of two: n2. But a set of entangled qubits can hold all the possible values of the qubits at the same time. For this reason, the number of states that a quantum computer can hold is represented by two to the power of qubits, n: 2n. For example, to represent a million possible states would require 1,000 bits but only 20 qubits.
Today’s computers contain billions of bits, but we have to throw a lot of them at our most complex problems to get anywhere. Today’s quantum computers have a small number of qubits — a recent IBM quantum computer release clocked in with 433 — but we need only a few hundred qubits to begin tackling very complex problems.
The power of today’s quantum computers is limited by errors and short coherence times. But as these factors are addressed, the results are likely to be amazing.
Examining What Quantum Computing Will Do for People
It’s easy to spend time geeking out on the strangeness and power of quantum computing. But what difference will quantum computing make to humanity?
To understand the answer, we first have to address a common misconception. People today tend to worry about how powerful today’s computers are: to worry about the power of the internet, social media, and machine learning and AI.
But there’s also a big problem around how powerful today’s computers aren’t: They simply aren’t up to big computational challenges in areas such as better batteries to fight climate change, better aerodynamics, better routing in complex transportation networks, and better discovery of new drugs, to name a few important examples. (See Chapters 13 and 14 for more information on the challenges that quantum computing will be able to help people to address.)
And these big computational challenges are exactly the areas where we expect quantum computing to make a big difference. Future quantum computers will be able to solve problems we can’t touch today, and to do so far faster, more cheaply, and with less energy expenditure than today’s computers.
Quantum computers can only “do their thing” in partnership with computers of the kind we use today. So when you see descriptions of what quantum computing can do, understand that these accomplishments will also require a whole lot of conventional computing power.
IS SCHRÖDINGER’S CAT FOR REAL?
No, Schrödinger's cat isn't real. But let’s add a bit of nuance to that answer.
Quantum mechanics, the physics that power quantum computing, has been driving people batty since the core theoretical work was done between 1900 and 1930. (See Chapter 3 for details.) And nothing symbolizes this confusion better than Schrodinger’s cat.
Erwin Schrödinger, the brilliant physicist behind the Schrödinger’s cat thought experiment, was trying to disprove quantum computing when he came up with it in 1935. But he actually summed up the mystery behind all things quantum better than anyone, ever.
In the Schrödinger’s cat thought experiment, a vial of radioactive poison, some decaying radioactive mass, and a cat are all placed in a box by a scientist. At some point, radioactive decay will release a hammer that breaks the flask, killing the cat, as shown in the figure. But radioactive decay is random, so no one can predict just when the hammer will break the flask.
So the scientist closes the box and goes away, and then waits several hours before coming back. During those hours, an urgent question arises: Is the cat alive or dead?
Quantum mechanics offers only a gnomic answer: yes and no. No intelligence in the world can say for sure whether or not the radioactive decay will kill the cat at a particular moment. So the cat is seen as being both dead and alive until the scientist comes back and opens the box.
This seemingly ridiculous conjecture demonstrates superposition, in which matter — in this case, the body of a feline — is in two states at once. Superposition, which is critical to quantum computing, has been proven to be real innumerable times since Schrödinger first came up with his thought experiment. (Cats are actually too large, and too embedded within our material world, to be in superposition, in case you were worried. And once again, NO CATS WERE HARMED. Meow.)
A related principle, entanglement — a mysterious connection between arbitrarily distant particles, though not cats — has also been proven, in a series of experiments that were recognized with the Nobel Prize for Physics in 2022. It was Einstein who described entanglement in particular, and quantum mechanics in general, as “spooky action at a distance.”
So Schrödinger’s cat — in the sense of actual cats being placed in mortal danger — is not real. But the principles that animate Schrödinger’s immortal thought experiment are very real indeed, as is proven every day in quantum computing.
Describing Different Types of Quantum Computing
There are three ways to do quantum-type computing, and all of them are actively being used and investigated today. They are described in some detail in Chapters 8 through 11; we briefly describe them here.
Quantum-inspired computing
Classical computers are based on logic gates, which take in electrical currents and apply binary logic to them to produce either no outgoing current (a 0) or an easily measurable current (a 1) as a result. By breaking down any mathematical or logical problem to a low enough level and running it through logic gates, you can come up with an answer.
When insights from quantum computing are used to create new algorithms that run on classical computers, or when quantum computer simulators are run on classical computers, this is called quantum-inspired computing, as described in Chapter 8. Quantum-inspired computing has proven to be a productive approach to finding new solutions at this early point in the development of quantum computing.
Quantum annealing
In classical computing, there’s an approach called simulated annealing. It’s analogous to annealing in metallurgy, in which a metal is heated to melt its internal structure, and then cooled to yield a softer, easier-to-work result. Simulated annealing is good for solving optimization problems, such as the least expensive route for visiting a number of cities. A similar process to this can be used to solve problems by putting a set of equations through a series of transformations until a result appears.
The quantum computing version of this approach is called quantum annealing. Quantum annealing doesn’t use a gate-based quantum computing approach, which is more advanced but harder to implement, as described in Chapters 10 and 11. Instead, quantum annealing uses qubits as a group to solve optimization problems, which is a less demanding use of qubits.
Quantum annealers allow for qubit errors and return results that are inexact but still useful in many cases. For instance, a quantum annealer might identify a very good way to route a fleet of delivery trucks, rather than delivering the one and only best possible routing. Only one substantial company, D-Wave, makes quantum computers that use the quantum annealing approach — and they have recently announced plans to make logic-gate quantum computers as well.
Quantum annealers were criticized at one point as not being actual quantum computers, but that is no longer the case. However, gate-based quantum computers get most of the attention, research effort, and investment.
