SCIENCE/PHYSICS Schrödinger’s Killer App Schrödinger’s Killer App Race to Build the World’s First Quantum Computer Race to Build the World’s First Quantum Computer Written by a renowned quantum physicist closely involved in the U.S. government’s development of quantum information science, Schrödinger’s Killer App: Race to Build the World’s First Quantum Computer presents an inside look at the government’s quest to build a quantum computer capable of solving complex mathematical problems and hacking the public-key encryption codes used to secure the Internet. The “killer app” refers to Shor’s quantum factoring algorithm, which would unveil the encrypted communications of the entire Internet if a quantum computer could be built to run the algorithm. Schrödinger’s notion of quantum entanglement—and his infamous cat—is at the heart of it all. The book develops the concept of entanglement in the historical context of Einstein’s 30-year battle with the physics community over the true meaning of quantum theory. It discusses the remedy to the threat posed by the quantum code breaker: quantum cryptography, which is unbreakable even by the quantum computer. The author also covers applications to other important areas, such as quantum physics simulators, synchronized clocks, quantum search engines, quantum sensors, and imaging devices. In addition, he takes readers on a philosophical journey that considers the future ramifications of quantum technologies. Interspersed with amusing and personal anecdotes, this book presents quantum computing and the closely connected foundations of quantum mechanics in an engaging manner accessible to non-specialists. Requiring no formal training in physics or advanced mathematics, it explains difficult topics, including quantum entanglement, Schrödinger’s cat, Bell’s inequality, and quantum computational complexity, using simple analogies. K14277 ISBN: 978-1-4398-9673-0 9 0 0 0 0 Jonathan P. Dowling 9 781439 896730 K14277_Cover_mech.indd 1 3/19/13 11:09 AM Schrödinger’s Killer App Race to Build the World’s First Quantum Computer Schrödinger’s Killer App Race to Build the World’s First Quantum Computer Jonathan P. Dowling Boca Raton London New York CRC Press is an imprint of the Taylor & Francis Group, an informa business Taylor & Francis Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2013 by Taylor & Francis Group, LLC Taylor & Francis is an Informa business No claim to original U.S. Government works Version Date: 20130226 International Standard Book Number-13: 978-1-4398-9674-7 (eBook - PDF) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. 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Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com Dedicated to My Parents Patricia Mary Dowling and John Philip Dowling Contents Preface ix 1 The Early Years—When Einstein Attacks! 1 Certain Uncertainties 5 All I’m Ever Going to Be Is Incomplete 7 Fairies, Gremlins, and Magic Dice 19 e Inverted Earth Society 28 e Cat in the App 35 2 For Whom the Bell Tolls 49 Clanking Contraptions and Cantankerous Codgers 55 Freedom of Choice, French Finesse, and Loopholes 63 I Never Metaphysics I Didn’t Like 71 3 The Quantum Codebreaker 77 e Trouble with ulium 82 Turing Machines and a Deutsch Treat 91 Your Pad or Mine? 106 e People’s Key 113 e Bolt from the Blue 120 4 You’re in the Army Now 131 e Great Quantum Diaspora 132 e Notebook, e Spy, and e Workshop 134 e Unlying Lands 171 Interior Panel Siding 178 Needle in a Haystack 179 Quantum Computing in a Coee Cup—When the Buzz Wears O 192 D-Wave, BOSS, D-Wave 207 5 More Gadgets from the Quantum Spookhouse 227 Blessed Are the Codemakers 227 Quantum Repeaters and Earth-to-Space Quantum Cryptography 245 vii viii Contents Beam Me Up, Charlie 256 e Tale of the True Timepiece 274 From Quantum Computers to Quantum Sensors 283 Light Blips Shrink Chips 299 e Great Clock Synchronization Saga 308 6 Hilbert Space—The Final Frontier 327 Quantum Technology in a FLASH 327 Qubits, Four Bits, Six Bits, a Dollar 355 e Church of the Larger Hilbert Space 378 To Go Where No Mad Scientist Has Gone Before 396 PREFACE Since 1994, I have been closely involved in the development of quantum infor- mation science in the United States. I was co-organizer of the rst Department of Defense (DoD) workshop on the topic (held in Tucson in 1995), and from 1994 through 1998, I served as a DoD reviewer of the program. From 1998 through 2004, I continued in this role as a scientist at the NASA Jet Propulsion Laboratory. From 2004 to the present, I have served as a scientic academic reviewer of quantum technologies for the government in my current post at Louisiana State University. (Geaux Tigers!) is book consists of my personal history of the development of the eld of quantum computing in the United States, constructed primarily from memory and detailed notes, from my point of view as a quantum physicist and a member of the DoD advisory programs. e “killer app” (or “killer application”) in the title refers to Shor’s quantum factoring algorithm, which—if only a quantum computer could be built to run it—would unveil the encrypted communications of the entire Internet for all to see. (Your credit card number would never be safe again.) I call this algorithm Schrödinger’s Killer App, instead of Shor’s Killer App, because Schrödinger’s notion of quantum entanglement is at the heart of it all (and as an alliterative allusion to Schrödinger’s infamous half-alive and half-dead cat). From international multi-billion-dollar nancial transactions to top-secret government communications, all would be vulnerable to such a quantum code breaker. us, the race is on to be the rst to construct one, as the winner will hold the key to the entire Internet. My particular history leads me to focus on the US government’s role in all this, specically the DoD and other intelligence agencies that are vitally interested in the secret-code-breaking ability of the quantum computer. To keep myself out of hot water (and keep my friends and colleagues at such agencies from despair), when referring to real persons in this book, particu- larly those in the intelligence agencies, I resort to a rst-name-only reference (or rst name with last initial in case of confusion). I take full responsibility for any errors in fact or ction contained herein. (I am Irish, and under Irish rules, the truth or falsehood of a story always plays second ddle to the entertain- ment value that it has and the moral that it provides. And yes—I have kissed the Blarney stone.) ix x Preface In these pages, I also discuss the remedy to the potential threat posed by the quantum code breaker—quantum cryptography, which is unbreakable even by the quantum computer. While code breaking is the focus of my work here, I also discuss applications to important yet more mundane tasks such as the development of quantum physics simulators, synchronized clocks, quantum search engines, and quantum sensors and imaging devices. (I also tell embar- rassing stories about myself as well as embarrassing stories about others.) is book is meant to appeal to the layperson who is interested in quan- tum physics and quantum computing but who has no formal training in either physics or advanced mathematics. I have therefore attempted to explain some- what dicult notions—such as quantum entanglement, Schrödinger’s cat, Bell’s inequality, and quantum computational complexity—by simple analo- gies, which require no physics schooling and little or no mathematics to grasp. Since mathematics is what gives accuracy to such physical notions, I realize that my analogies will not be completely technically accurate. (For this I am sure to get complaints from my physics colleagues, and I apologize to them in advance.) But I assure you my analogies are correct in spirit, and it is in this spirit that I intend to engage the less technically inclined reader. (Quantum physicists should only read this for the jokes.) I know I will not make both camps absolutely happy.