by John Gribbin
15. Using the best computers available at the time of writing, summer 2012.
16. Long ago, I used this application of the technique in the work for my PhD thesis.
17. His emphasis.
18. In fairness, although I personally like the MWI, I should acknowledge that proponents of alternative interpretations are equally convinced that only “their” view is right. See my book Schrödinger's Kittens. As Winfried Hensinger commented to me, “How can you quantify weirdness? We should not forget our intuition is based in a classical world, so it will always mislead us in any interpretation of quantum physics.”
19. It has even been suggested that our Universe is a simulation running on a quantum computer; see In Search of the Multiverse.
20. Just such an algorithm has now been discovered; see http://www.scottaaronson.com/blog/?p=207.
21. The P stands for “polynomial time.”
22. For “nondeterministic polynomial time.”
23. This is a version of the “traveling salesman problem.”
24. That is, as still as is allowed by quantum uncertainty.
25. Not to be confused with the quantum pioneer Wolfgang Pauli.
26. In the sense of being made in one piece.
27. 16 = 24.
28. This really has been done. See next chapter. It has also been done with ions, on a much smaller scale.
29. I should mention that Steane is not a proponent of the MWI and that this remark is my own.
30. The spin is a property of the nucleus, but sometimes people—myself included—refer sloppily to the spin of the atom.
CHAPTER 6: TURING'S HEIRS AND THE QUANTUM MACHINES
1. See his contribution to Bernstein and Lo (eds.), Scaleable Quantum Computers. Also arXiv:quant-ph/0002077v3, “The Physical Implementation of Quantum Computation.”
2. All the other techniques require some kind of breakthrough in terms of the physics to become viable, but every aspect of the ion trap technique has been tried and tested. The problems that remain are engineering problems, and funding. Given money and time, we can be sure an ion-trap quantum computer will be built. The question is whether a physics breakthrough will enable another technique to get there first.
3. The Guardian, September 30, 2001.
4. Technically, superconducting Cooper pairs of electrons.
5. Essentially, phase tells you if waves are in step with one another.
6. New York Times, February 28, 2012.
7. See more at: http://www.theage.com.au/technology/sci-tech/tiny-dot-speeds-hitech-future-20100524-w4bi.html#ixzz27fftbDQE.
8. It's convenient to think of a single electron occupying a quantum dot; in practice, it may be that there are several electrons in each quantum dot, with one more in one dot than the other.
9. At least, for electrons and other so-called “spin half” systems. I shall return to this shortly.
10. Nature, vol. 489 (September 27, 2012), pp. 541–5.
11. Science, vol. 336, no. 6086 (June 8, 2012).
12. Specifically, phosphorus-39.
13. Protons and neutrons themselves are composed of quarks, but happily we do not have to go down to that level of detail here.
14. Fluids are preferred to solids because they have no special structure to complicate calculations, unlike crystals, for example.
15. The tortoise put on a bit of a spurt itself in 2009, when a team at NIST developed a two-qubit system that could carry out any of 160 different operations on demand, making it in effect the world's first programmable quantum computer.
16. Scientific American, August 2008.
17. Europe, Canada and Japan have similar plans in the pipeline.
18. Richard Feynman once said that he would like to write a popular book, but couldn't decide whether it should be entitled Fun with Fysics or Phun with Physics. I have (barely) resisted the equivalent temptation here.
19. Never forget, though, that those “standard industrial techniques” require the use of computers to control the operations.
20. Science Express (online), March 27, 2008.
21. This is (slightly) optimistic; most people I spoke to who work in the field think you would need around 50 qubits to solve problems a classical computer cannot do.
22. See my book Schrödinger's Kittens.
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http://libweb.princeton.edu/libraries/firestone/rbsc/finding_aids/mathoral/pmcxrota.htm
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Every effort has been made to trace the copyright holders of photos reproduced in the book. Copyright holders not credited are invited to get in touch with the publishers.
PHOTOS IN THE TEXT
7: the Granger Collection, New York; 9: King's College Library, Cambridge/AMT/K/7/12; 53: Time & Life Pictures/Getty Images; 97: provided with kind permission of Dr. Tonomura; 99: CERN/Science Photo Library; 135: © 1982 CERN; 181: Winfried Hensinger, University of Sussex; 183: Lulie Tanett; 226: Getty Images
PHOTO INSERT
Credits are listed clockwise on each spread, starting from the top left.
Alan Turing on Waterloo Station, c. 1926 (detail): King's College Library, Cambridge/AMT/K/7/3; Letter from Alan Turing, April 1, 1923: King's College Library, Cambridge/AMT/K/1/1, © P. N. Furank; Alan Turing finishing a race: National Physical Laboratory © Crown copyright/Science Photo Library
Hut 3, Bletchley Park: © Edifice/Corbis; Colossus, 1943: SSPL via Getty Images; codebreakers, Bletchley Park, c. 1942: SSPL via Getty Images
ENIAC: Associated Press; advertisement for the Bendix G-15 computer: courtesy of the Computer History Museum; J. Robert Oppenheimer and John von Neumann: Emilio Segre Visual Archives/American Institute of Physics/Science Photo Library
Fred Hoyle: BBC Photo Library; bio-wall: Philippe Plailly/Science Photo Library
Fifth Solvay Physics Conference, Brussels, 1927: SSPL via Getty Images; quantum cryptography equipment: Volker Steger/Science Photo Library; MRI scanner, 2010: Boston Globe via Getty Images; double-slit refraction: GIPhotostock/Science Photo Library
John Stewart Bell, 1989: Corbin O'Grady Studio/Science Photo Library; David Bohm, 1971: Getty Images; Alain Aspect: Österreichische Zentralbibliothek für Physik (Austrian Central Library for Physics); Hans Georg Dehmelt: Emilio Segre Visual Archives/American Institute of Physics/Science Photo Library
Brian Josephson, November 23, 1973: PA/PA Archive/Press Association Images; David Wineland adjusting an ultraviolet laser, 2003: © Geoffrey Wheeler/National Institute of Standards and Technology; Nobel laureates David J. Wineland and Serge Haroche, December 2012: AFP/Getty Images; Gary Kasparov vs. a computer, May 3, 1997: AFP/Getty Images
Ion trap laboratory and chip: Winfried Hensinger, University of Sussex
Aberdeen Proving Ground, 68, 74, 76, 79
Abramson, Albert, 72
ACE (Automatic Computing Engine), 47–8, 50
Adleman, Len, 204
Aharonov, Yakir, 163, 164
Aiken, Howard, 69
American Physical Society, 165, 166
American Telephone and Telegraph Company (AT&T), 33
ancilla, 222–3
Anderson, Philip, 232–4
artificial intelligence, 82
Aspect, Alain, 168–74
Atkins, James, 16
Atomic Energy Research Establishment (AERE), 149, 152, 153–4
atoms: cavity quantum electrodynamics, 227, 260–2; donor, 246, 247; Manhattan Project, 63; manipulation of, 1, 217, 224–5, 243; nanotechnology, 94; NMR, 250–1; number in visible Universe, 208; quantum computing, 134; quantum dots, 242–3
automata, 83; cellular model, 85–6; self-reproducing, 84–6
Bader, Abram, 113–14
ballistics, 67–8, 73
Bates, Audrey, 49
Bell, John Stewart: Aspect's visit, 171; career, 152, 153–5; childhood, 149–50; death, 174; education, 150–2; on experiments, 169–70; on FAPP, 106; Feynman's work, 133; on “hidden variables” theory, 137; on “many-universes interpretation,” 174–5, 185–6; marriage, 152–3; Nobel nomination, 174; refutation of von Neumann's argument, 156–7; on wave function, 184; writings: “On the Einstein-Podolsky-Rosen Paradox,” 158–62, 163, 171; “On the Problem of Hidden Variables in Quantum Mechanics,” 156–7, 165; see also Bell's inequality, Bell's theorem
Bell, Mary, 152–3, 154–5
Bell Laboratories, 33, 69, 125, 233
Bell-state measurement, 257
Bell's inequality, 159; Aspect's work, 172; Chinese experiments, 258; Clauser's work, 166, 167; Feynman's work, 133; Fry's work, 168; Holt's work, 165, 167–8; Horne's work, 164; teleportation, 256
Bell's theorem, 159, 174, 189; Aspect's work, 171–3; Clauser and Freedman's work, 166–7, 171; Fry's work, 168; Holt's work, 167–8; Josephson's work, 231; Shimony and Horne's work, 164; testing, 161, 163, 164, 166–70
Bendix Corporation, 48
Benioff, Paul, 131–2, 134
Bennett, Charles, 128, 129, 196
Berkeley, University of California at, 145–6, 164, 166, 204, 253
Berlin, University of, 55–6
Bernstein, Jeremy, 150, 154
Bigelow, Julian, 23, 85
Billings, John, 66
binary code, 18–19
Birkbeck College, Londo
n, 51, 149
Birmingham University, 152, 153
bits (binary digits), 2, 134, 176, 242
Bletchley Park, 29–35, 37–9, 41–3, 44, 204
Bliss, Gilbert, 74
Bohm, David: career, 145–6, 148–9; on entanglement, 163; on EPR puzzle, 146–8; on hidden variables, 147–9, 156; influence, 154, 157, 164, 165, 170; writings: Quantum Theory, 146–8
Bohr, Niels: Copenhagen institute, 59, 105; Copenhagen Interpretation, 105, 138, 142, 145, 146
Bombas, 28–9, 30
Bombes, 28, 30–3, 40
Boole, George, 123
Boolean algebra, 123
Born, Max, 106, 151–2, 154, 162
bosons, 176, 178
Boston University, 163
Boulder, Colorado, 216, 219, 220, 253
BQP (bounded-error quantum polynomial) problems, 213
Brandeis University, 155, 161
Brewster, Edwin, 11–12
Bristol, University of, 264–5
British Tabulating Machine Company, 30–1
Bronowski, Jacob, 89
Brooker, Tony, 50
Brown, Julian, 207
Budapest, University of, 55–6
Burks, Arthur, 79
bus, 79–80; quantum, 240
bytes, 2–3
Caltech, 130, 133, 145
Cambridge University, 16–21, 77, 231
carbon-13, 248–9
cathode ray tubes, 72–3
cavity quantum electrodynamics (CQED), 227, 260
central processing unit (CPU), 79
Center for Quantum Computation, Oxford, 190
Center for Quantum Photonics, Bristol, 264–5
CERN, 153, 154–5
charge qubit, 243
chess, 92, 210–12
Children's Hour (BBC), 50
chips, 90, 91
CHSH paper, 166
Chuang, Isaac, 223
Church, Alonzo, 21, 22, 23
Church-Turing principle, 196
Churchill, Winston, 43–4
CIP Technologies, 264
ciphers and codes: Enigma, 25–30; one time pad, 203–4; quantum computers, 1, 203–10, 213, 266; Shor's algorithm, 206–9, 210, 212, 213; speech encipherment, 33, 34; Tunny, 35–40, 44; Turing's early work, 23–4
Cirac, Juan Ignacio, 216–17, 220
Clark, Terry, 235
Clarke, Joan, 33
