Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Measurements on the reality of the wavefunction

Abstract

Quantum mechanics is an outstandingly successful description of nature, underpinning fields from biology through chemistry to physics. At its heart is the quantum wavefunction, the central tool for describing quantum systems. Yet it is still unclear what the wavefunction actually is: does it merely represent our limited knowledge of a system, or is it in direct correspondence to reality? Recent no-go theorems argued that if there was any objective reality, then the wavefunction must be real. However, that conclusion relied on debatable assumptions. Here we follow a different approach without these assumptions and experimentally bound the degree to which knowledge interpretations can explain quantum phenomena. Using single photons, we find that no knowledge interpretation can fully explain the limited distinguishability of non-orthogonal quantum states in three and four dimensions. Assuming that a notion of objective reality exists, our results thus strengthen the view that the wavefunction should directly correspond to this reality.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Figure 1: Ontological models for quantum theory.
Figure 2: Scheme for probing the reality of the wavefunction.
Figure 3: Experimental results.
Figure 4: Prepared states and measurement errors for n = 7.

References

  1. 1

    Mermin, N. D. Is the moon there when nobody looks? Reality and the quantum theory. Phys. Today 38(4), 38–47 (1985).

    Article  Google Scholar 

  2. 2

    Mermin, N. D. QBism puts the scientist back into science. Nature 507, 421–423 (2014).

    ADS  Article  Google Scholar 

  3. 3

    Caves, C. M., Fuchs, C. A. & Schack, R. Quantum probabilities as Bayesian probabilities. Phys. Rev. A 65, 022305 (2002).

    ADS  MathSciNet  Article  Google Scholar 

  4. 4

    Fuchs, C. A. QBism, the Perimeter of Quantum Bayesianism. Preprint at http://arXiv.org/abs/1003.5209 (2010).

  5. 5

    Spekkens, R. Evidence for the epistemic view of quantum states: A toy theory. Phys. Rev. A 75, 032110 (2007).

    ADS  Article  Google Scholar 

  6. 6

    Leifer, M. S. Is the quantum state real? An extended review of ψ-ontology theorems. Quanta 3, 67–155 (2014).

    Article  Google Scholar 

  7. 7

    Harrigan, N. & Spekkens, R. W. Einstein, incompleteness, and the epistemic view of quantum states. Found. Phys. 40, 125–157 (2010).

    ADS  MathSciNet  Article  Google Scholar 

  8. 8

    Einstein, A., Podolsky, B. & Rosen, N. Can quantum-mechanical description of physical reality be considered complete? Phys. Rev. 47, 777–780 (1935).

    ADS  Article  Google Scholar 

  9. 9

    Bell, J. S. On the Einstein–Podolsky–Rosen paradox. Physics 1, 195–200 (1964).

    MathSciNet  Article  Google Scholar 

  10. 10

    Brunner, N., Cavalcanti, D., Pironio, S., Scarani, V. & Wehner, S. Bell nonlocality. Rev. Mod. Phys. 86, 419–478 (2014).

    ADS  Article  Google Scholar 

  11. 11

    Pusey, M. F., Barrett, J. & Rudolph, T. On the reality of the quantum state. Nature Phys. 8, 476–479 (2012).

    ADS  Article  Google Scholar 

  12. 12

    Colbeck, R. & Renner, R. Is a system’s wave function in one-to-one correspondence with its elements of reality? Phys. Rev. Lett. 108, 150402 (2012).

    ADS  Article  Google Scholar 

  13. 13

    Hardy, L. Are quantum states real? Int. J. Mod. Phys. B 27, 1345012 (2013).

    ADS  MathSciNet  Article  Google Scholar 

  14. 14

    Patra, M. K., Pironio, S. & Massar, S. No-go theorems for ψ-epistemic models based on a continuity assumption. Phys. Rev. Lett. 111, 090402 (2013).

    ADS  Article  Google Scholar 

  15. 15

    Aaronson, S., Bouland, A., Chua, L. & Lowther, G. ψ-epistemic theories: The role of symmetry. Phys. Rev. A 88, 032111 (2013).

    ADS  Article  Google Scholar 

  16. 16

    Colbeck, R. & Renner, R. A system’s wave function is uniquely determined by its underlying physical state. Preprint at http://arxiv.org/abs/1312.7353 (2013).

  17. 17

    Emerson, J., Serbin, D., Sutherland, C. & Veitch, V. The whole is greater than the sum of the parts: On the possibility of purely statistical interpretations of quantum theory. Preprint at http://arxiv.org/abs/1312.1345 (2013).

  18. 18

    Lewis, P. G., Jennings, D., Barrett, J. & Rudolph, T. Distinct quantum states can be compatible with a single state of reality. Phys. Rev. Lett. 109, 150404 (2012).

    ADS  Article  Google Scholar 

  19. 19

    Barrett, J., Cavalcanti, E. G., Lal, R. & Maroney, O. J. E. No ψ-epistemic model can fully explain the indistinguishability of quantum states. Phys. Rev. Lett. 112, 250403 (2014).

    ADS  Article  Google Scholar 

  20. 20

    Leifer, M. S. ψ-epistemic models are exponentially bad at explaining the distinguishability of quantum states. Phys. Rev. Lett. 112, 160404 (2014).

    ADS  Article  Google Scholar 

  21. 21

    Branciard, C. How ψ-epistemic models fail at explaining the indistinguishability of quantum states. Phys. Rev. Lett. 113, 020409 (2014).

    ADS  Article  Google Scholar 

  22. 22

    Nigg, D. et al. Can different quantum state vectors correspond to the same physical state? An experimental test. Preprint at http://arxiv.org/abs/1211.0942 (2012).

  23. 23

    Boschi, D., Branca, S., De Martini, F., Hardy, L. & Popescu, S. Experimental realization of teleporting an unknown pure quantum state via dual classical and Einstein–Podolsky–Rosen channels. Phys. Rev. Lett. 80, 1121–1125 (1998).

    ADS  MathSciNet  Article  Google Scholar 

  24. 24

    Patra, M. K. et al. Experimental refutation of a class of ψ-epistemic models. Phys. Rev. A 88, 032112 (2013).

    ADS  Article  Google Scholar 

  25. 25

    Larsson, J-Å. Loopholes in Bell inequality tests of local realism. J. Phys. A 47, 424003 (2014).

    MathSciNet  Article  Google Scholar 

  26. 26

    Fujiwara, M., Takeoka, M., Mizuno, J. & Sasaki, M. Exceeding the classical capacity limit in a quantum optical channel. Phys. Rev. Lett. 90, 167906 (2003).

    ADS  Article  Google Scholar 

  27. 27

    Bohm, D. A suggested interpretation of the quantum theory in terms of “Hidden” variables. I. Phys. Rev. 85, 166–179 (1952).

    ADS  MathSciNet  Article  Google Scholar 

  28. 28

    Everett, H. III “Relative State” formulation of quantum mechanics. Rev. Mod. Phys. 29, 454–462 (1957).

    ADS  MathSciNet  Article  Google Scholar 

  29. 29

    James, D. F. V., Kwiat, P. G., Munro, W. J. & White, A. G. Measurement of qubits. Phys. Rev. A 64, 52312 (2001).

    ADS  Article  Google Scholar 

  30. 30

    Fedrizzi, A., Herbst, T., Poppe, A., Jennewein, T. & Zeilinger, A. A wavelength-tunable fiber-coupled source of narrowband entangled photons. Opt. Express 15, 15377 (2007).

    ADS  Article  Google Scholar 

Download references

Acknowledgements

We thank M. S. Leifer, J. Barrett, O. J. E. Maroney and R. Lal for insightful discussions and R. Muñoz for experimental assistance. This work was supported in part by the Centres for Engineered Quantum Systems (Grant No. CE110001013) and for Quantum Computation and Communication Technology (Grant No. CE110001027). A.G.W. acknowledges support from a University of Queensland Vice-Chancellor’s Senior Research Fellowship, C.B. from the ‘Retour Post-Doctorants’ program (ANR-13-PDOC-0026) of the French National Research Agency and a Marie Curie International Incoming Fellowship (PIIF-GA-2013-623456) of the European Commission, and C.B., E.G.C. and A.F. acknowledge support through Australian Research Council Discovery Early Career Researcher Awards (DE140100489, DE120100559 and DE130100240 respectively). This project was made possible through the support of a grant from Templeton World Charity Foundation, TWCF 0064/AB38. The opinions expressed in this publication are those of the author(s) and do not necessarily reflect the views of Templeton World Charity Foundation.

Author information

Affiliations

Authors

Contributions

A.F., A.G.W., C.B., E.C. and M.R. conceived the study. A.F., M.R. and B.D. designed the experiment. C.B. provided the lists of states and measurements to be used. M.R. and B.D. performed the experiment, collected and analysed the data. All authors contributed to writing the paper.

Corresponding author

Correspondence to A. Fedrizzi.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

Supplementary Information (PDF 5919 kb)

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Ringbauer, M., Duffus, B., Branciard, C. et al. Measurements on the reality of the wavefunction. Nature Phys 11, 249–254 (2015). https://doi.org/10.1038/nphys3233

Download citation

Further reading

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing