Dialogue concerning two views on quantum coherence: factist and fictionist. S. D. Bartlett, T. Rudolph and R. W. Spekkens in Int. J. Quantum Inform. 04:17 (2006).  What the paper says!?

Bartlett06a-abstract.png

The text concerns the problem whether coherent states have a phase or not.

It confronts «the two camps by opposing slogans: “coherence as fact” versus “coherence as fiction."

Takes no strong side: «The arguments for both sides of the debate are sufficiently compelling that it is easy to find oneself (and indeed we have found ourselves) defending different positions at different times.»

But they still offer a resolution through "reference frames":

In the context of the argument of the dialogue, our claim is that the phase of an optical mode is an extrinsic property of that mode, only defined in relation to an external phase reference, and the fact that there are many possible choices for this phase reference is the source of the debate.
Screenshot 20250203 235809.png

The following is a quick introduction to Reference Frames.

In quantum theory, treating an RF internally requires introducing a Hilbert space for it. Treating it externally usually implies that it is being treated classically.
It appears to us highly likely, however, that quantum theory, as it is currently formulated, applies only to subsystems of the universe. This is not to say that we reject the idea of theories that apply to the universe as a whole; we only reject the idea that quantum theory as it stands is such a theory.

The conclusion is that everybody is right, once they know what frame they are dealing with.

There is a nice overview of platforms where the debate took place:

  • Initially for BCS:
    • 2. P. W. Anderson, in The Lesson of Quantum Theory, eds. J. D. Boer, E. Dal, O. Ulfbeck (Elsevier, Amsterdam, 1986), pp. 2333.
    • 3. R. Haag, Il Nuovo Cimento XXV (1962) 2695.
    • 4. D. Kershaw and C. H. Woo, Phys. Rev. Lett. 33 (1974) 918.
  • For atomic BEC:
    • 5. J. Javanainen and S. M. Yoo, Phys. Rev. Lett. 76 (1996) 161.[1]
    • 6. W. Hoston and L. You, Phys. Rev. A 53 (1996) 4254.[2]
    • 7. S. M. Yoo, J. Ruostekoski and J. Javanainen, J. Mod. Opt. 44 (1997) 1763.[3]
    • 8. Y. Castin and J. Dalibard, Phys. Rev. A 55 (1997) 4330.[4]
  • For quantum optics (Early versions): (should probably also mention L. Vaidman's reply.[5])
    • 10. L. Hardy, Phys. Rev. Lett. 73 (1994) 2279.[6]
    • 11. D. M. Greenberger, M. A. Horne and A. Zeilinger, Phys. Rev. Lett. 75 (1995) 2064.[7]
    • 12. L. Hardy, Phys. Rev. Lett. 75 (1995) 2065.[8]
  • Quantum optics (Modern versions, K. Molmer):
    • 13. K. Mølmer, Phys. Rev. A 55 (1997) 3195.[9]
    • 14. K. Mølmer, J. Mod. Opt. 44 (1997) 1937.[10]
  • and its aftermath:
    • 15. J. Gea-Banacloche, Phys. Rev. A 58 (1998) 4244.[11]
    • 16. K. Mølmer, Phys. Rev. A 58 (1998) 4247.[12]
    • 17. T. Rudolph and B. C. Sanders, Phys. Rev. Lett. 87 (2001) 077903.[13]
    • 18. S. J. van Enk and C. A. Fuchs, Phys. Rev. Lett. 88 (2002) [sic]should be (2001) 027902.[14]
    • 19. T. Rudolph and B. C. Sanders, quant-ph/0112020 (2001).[15]
    • 20. S. J. van Enk and C. A. Fuchs, Quant. Inf. Comput. 2 (2002) 151.[16]
    • 21. K. Nemoto and S. L. Braunstein, quant-ph/0207135 (2002).[17]
    • 22. K. Nemoto and S. L. Braunstein, Phys. Rev. A 68 (2003) 042326.[18]
    • 23. K. Nemoto and S. L. Braunstein, Phys. Lett. A 333 (2004) 378.[19]
    • 24. B. C. Sanders, S. D. Bartlett, T. Rudolph and P. L. Knight, Phys. Rev. A 68 (2003) 042329.[20]
    • 25. H. M. Wiseman, J. Mod. Opt. 50 (2003) 1797.[21]
    • 26. H. M. Wiseman, quant-ph/0104004 (2001).[22]
    • 27. H. M. Wiseman, J. Opt. B 6 (2004) S849.[23]
    • 28. M. Fujii, Phys. Rev. 68 (2003) 050302(R).[24]
    • 29. R. W. Spekkens and J. E. Sipe, in Coherence and Quantum Optics VIII, eds. N. Bigelow et al. (Kluwer Academic, New York, 2003), p. 465.[25]
    • 30. J. Smolin, quant-ph/0407009 (2004).[26]
In addition to what has appeared in the literature, there have been a great number of debates on this issue at various conferences and among workers in the field, which supplement the arguments found in the literature.

The text is dedicated to the memory of A. Peres.

References

  1. ↑ Quantum Phase of a Bose-Einstein Condensate with an Arbitrary Number of Atoms. J. Javanainen and S. M. Yoo in Phys. Rev. Lett. 76:161 (1996).
  2. ↑ Interference of two condensates. W. Hoston and L. You in Phys. Rev. A 53:4254 (1996).
  3. ↑ Interference of two Bose-Einstein condensates. S. M. Yoo, J. Ruostekoski and J. Javanainen in J. Mod. Opt. 44:1763 (1997).
  4. ↑ Relative phase of two Bose-Einstein condensates. Y. Castin and J. Dalibard in Phys. Rev. A 55:4330 (1997).
  5. ↑ Nonlocality of a Single Photon Revisited Again. L. Vaidman in Phys. Rev. Lett. 75:2063 (1995).
  6. ↑ Nonlocality of a Single Photon Revisited. L. Hardy in Phys. Rev. Lett. 73:2279 (1994).
  7. ↑ Nonlocality of a Single Photon?. D. M. Greenberger, M. A. Horne and A. Zeilinger in Phys. Rev. Lett. 75:2064 (1995).
  8. ↑ Hardy Replies. L. Hardy in Phys. Rev. Lett. 75:2065 (1995).
  9. ↑ Optical coherence: A convenient fiction. K. Molmer in Phys. Rev. A 55:3195 (1997).
  10. ↑ Quantum entanglement and classical behaviour. K. Molmer in J. Mod. Opt. 44:1937 (1997).
  11. ↑ Comment on "Optical coherence: A convenient fiction". J. Gea-Banacloche in Phys. Rev. A 58:4244 (1998).
  12. ↑ Reply to "Comment on 'Optical coherence: A convenient fiction'''. K. Molmer in Phys. Rev. A 58:4247 (1998).
  13. ↑ Requirement of Optical Coherence for Continuous-Variable Quantum Teleportation. T. Rudolph and B. C. Sanders in Phys. Rev. Lett. 87:077903 (2001).
  14. ↑ Quantum State of an Ideal Propagating Laser Field. S. J. v. Enk and C. A. Fuchs in Phys. Rev. Lett. 88:027902 (2001).
  15. ↑ https://arxiv.org/abs/quant-ph/0112020
  16. ↑ https://arxiv.org/abs/quant-ph/0111157
  17. ↑ https://arxiv.org/abs/quant-ph/0207135
  18. ↑ Quantum coherence in the presence of unobservable quantities. K. Nemoto and S. L. Braunstein in Phys. Rev. A 68:042326 (2003).
  19. ↑ Quantum coherence: myth or fact? K. Nemoto and S. L. Braunstein in Phys. Lett. A 333:378 (2004).
  20. ↑ Photon-number superselection and the entangled coherent-state representation. B. C. Sanders, S. D. Bartlett, T. Rudolph and P. L. Knight in Phys. Rev. A 68:042329 (2003).
  21. ↑ Comment: There is no unmet requirement of optical coherence for continuous-variable quantum teleportation. H. M. Wiseman in J. Mod. Opt. 50:1797 (2003).
  22. ↑ https://arxiv.org/abs/quant-ph/0104004
  23. ↑ Defending continuous variable teleportation: why a laser is a clock, not a quantum channel. H. M. Wiseman in J. Opt. B 6: (2004).
  24. ↑ Continuous-variable quantum teleportation with a conventional laser. M. Fujii in Phys. Rev. A 68:050302 (2003).
  25. ↑ On the detection of single mode quantum coherence at optical frequencies. R. W. Spekkens and J. E. Sipe in 🕮Coherence and Quantum Optics VIII page 465 (2003). [ISBN: 978-0-306-48116-1]
  26. ↑ https://arxiv.org/abs/quant-ph/0407009
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