Quantum computing

American Journal of Physics

Volumn 66, Issue 11, 1998, Pages 956-960

  Scarani, Valerio ^a  

^a EPFL   (Switzerland)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 0040577405     PISSN: 00029505     EISSN: None     Source Type: Journal    
DOI: 10.1119/1.19005     Document Type: Article

References (17)

1. D. Deutsch, "Quantum theory, the Church-Turing principle and the universal quantum computer," Proc. R. Soc. London Ser. A 400, 97-117 (1985). Deutsch was impressed by "quantum parallelism:" it seems as if many parallel computers were performing calculations, and that all these calculations contribute to the final result (the advised reader recognizes here the quantum computing version of the superposition principle). We read in the abstract of the paper: "The intuitive explanation of these properties places an intolerable strain on all interpretations of quantum theory other than Everett's." I feel that this was a very important topic in Deutsch's mind, possibly the main reason for him for proposing a new reading of quantum mechanics. Of course, the "intuitive explanation" proposed in the paper is not compelling at all; but we cannot avoid stressing that once again a great advance in science is due to somebody who tries to think physics, not only to make it.
2. P. W. Shor, "Algorithms for Quantum Computation: Discrete Logarithms and Factoring," Proceedings of the 35th Annual Simposium on the Foundations of Computer Science (IEEE Computer Society, Los Alamitos, 1994), pp. 124-134.
3. D. P. DiVincenzo, "Quantum computation and spin physics," J. Appl. Phys. 81, 4602-4607 (1997).
4. C. H. Bennett, "Quantum information and computation," Phys. Today 48, October 1995, pp. 24-30.
5. H. Weinfurter and A. Zeilinger, "Informationsübertragung und Informationsverarbeitung in der Quanten-welt," Phys. Bl. 52, 219-224 (1996).
6. M. Brune et al., "Observing the Progressive Decoherence of the "Meter" in a Quantum Measurement," Phys. Rev. Lett. 77, 4887-4890 (1996); a good simplified article written by the very authors of the experiment: S. Haroche et al., "Le chat de Schrödinger se prête à l'expérience," La Recherche 301, 50-55 (Septembre 1997) .
7. M. Brune et al., "Observing the Progressive Decoherence of the "Meter" in a Quantum Measurement," Phys. Rev. Lett. 77, 4887-4890 (1996); a good simplified article written by the very authors of the experiment: S. Haroche et al., "Le chat de Schrödinger se prête à l'expérience," La Recherche 301, 50-55 (Septembre 1997) .
8. In other words, the origin of decoherence lies in the possibility of obtaining information about the system by "performing a measurement" on the environment; a "measurement" being in fact any irreversible event, independent of the effective possibility for a human observer of detecting it. For a didactic approach, French-speaking readers can refer to J.-L. Basdevant; Problèmes de Mécanique Quantique (Ellipse, Paris, 1996), problème 5; in this model, decoherence occurs because of energy exchange, and it is shown that a single quantum of energy exchanged between the system and environment is enough to erase almost all information.
9. A. Barenco et al., "Elementary gates for quantum computation," Phys. Rev. A 52, 3457-3467 (1995).
10. Here you have three good reasons for this choice: (1) NMR is a standard experimental technique, contrarily, for instance, to cavity QED: many physicists and chemists are used to NMR, and those who are not can find excellent descriptions in many standard books (see, for instance, Ref. 10). (2) As discussed by Gershenfeld and Chuang (Ref. 11). NMR is up to now the only proposed method for QC involving very long decoherence times. (3) NMR is my own research field, and I am accustomed to explaining it to undergraduate students!
11. IV.
12. N. A. Gershenfeld and I. L. Chuang, "Bulk Spin-Resonance Quantum Computation," Science 275, 350-356 (1997).
13. pt = π at most), we can consider that no free evolution takes place while the perturbation is applied.
14. z by π/2, and not by π.
15. rt, 0
16. i, under the hypothesis that the whole system S admits the superposition principle.
17. K. Mattle et al., "Dense Coding in Experimental Quantum Communication," Phys. Rev. Lett. 76, 4656-4659 (1996).