Computing with Quantum Cats (33 page)

7
. In 1998 he was awarded the Dirac Prize of the Institute of Physics, in 2005 he received the Edge of Computation Science Prize worth $100,000, and in 2008 he was elected a Fellow of the Royal Society, with no check but plenty of kudos.

8
. See Davies and Brown,
The Ghost in the Machine
. Deutsch elaborated on the idea in his book
The Fabric of Reality
.

9
. The Copenhagen Interpretation was still conventional in 1982.

10
. If you want them, see
The Beginning of Infinity
.

11
. “Quantum Theory, the Church-Turing Principle and the Universal Quantum Computer,” in
Proceedings of the Royal Society
, vol. 400 (1985), pp. 97–117.

12
. His emphasis.

13
. There is no significance in the choice of decimal numbers; any different decimals will do.

14
. In practice the coding would be more sophisticated than this, as with Enigma, but this simple example makes the point.

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 = 2
⁴
.

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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WEB

http://libweb.princeton.edu/libraries/firestone/rbsc/finding_aids/mathoral/pmcxrota.htm

http://www.sussex.ac.uk/physics/iqt/virtualtour.html