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.
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Mermin, N. D. Is the moon there when nobody looks? Reality and the quantum theory. Phys. Today 38(4), 38–47 (1985).
Mermin, N. D. QBism puts the scientist back into science. Nature 507, 421–423 (2014).
Caves, C. M., Fuchs, C. A. & Schack, R. Quantum probabilities as Bayesian probabilities. Phys. Rev. A 65, 022305 (2002).
Fuchs, C. A. QBism, the Perimeter of Quantum Bayesianism. Preprint at http://arXiv.org/abs/1003.5209 (2010).
Spekkens, R. Evidence for the epistemic view of quantum states: A toy theory. Phys. Rev. A 75, 032110 (2007).
Leifer, M. S. Is the quantum state real? An extended review of ψ-ontology theorems. Quanta 3, 67–155 (2014).
Harrigan, N. & Spekkens, R. W. Einstein, incompleteness, and the epistemic view of quantum states. Found. Phys. 40, 125–157 (2010).
Einstein, A., Podolsky, B. & Rosen, N. Can quantum-mechanical description of physical reality be considered complete? Phys. Rev. 47, 777–780 (1935).
Bell, J. S. On the Einstein–Podolsky–Rosen paradox. Physics 1, 195–200 (1964).
Brunner, N., Cavalcanti, D., Pironio, S., Scarani, V. & Wehner, S. Bell nonlocality. Rev. Mod. Phys. 86, 419–478 (2014).
Pusey, M. F., Barrett, J. & Rudolph, T. On the reality of the quantum state. Nature Phys. 8, 476–479 (2012).
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).
Hardy, L. Are quantum states real? Int. J. Mod. Phys. B 27, 1345012 (2013).
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).
Aaronson, S., Bouland, A., Chua, L. & Lowther, G. ψ-epistemic theories: The role of symmetry. Phys. Rev. A 88, 032111 (2013).
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).
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).
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).
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).
Leifer, M. S. ψ-epistemic models are exponentially bad at explaining the distinguishability of quantum states. Phys. Rev. Lett. 112, 160404 (2014).
Branciard, C. How ψ-epistemic models fail at explaining the indistinguishability of quantum states. Phys. Rev. Lett. 113, 020409 (2014).
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).
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).
Patra, M. K. et al. Experimental refutation of a class of ψ-epistemic models. Phys. Rev. A 88, 032112 (2013).
Larsson, J-Å. Loopholes in Bell inequality tests of local realism. J. Phys. A 47, 424003 (2014).
Fujiwara, M., Takeoka, M., Mizuno, J. & Sasaki, M. Exceeding the classical capacity limit in a quantum optical channel. Phys. Rev. Lett. 90, 167906 (2003).
Bohm, D. A suggested interpretation of the quantum theory in terms of “Hidden” variables. I. Phys. Rev. 85, 166–179 (1952).
Everett, H. III “Relative State” formulation of quantum mechanics. Rev. Mod. Phys. 29, 454–462 (1957).
James, D. F. V., Kwiat, P. G., Munro, W. J. & White, A. G. Measurement of qubits. Phys. Rev. A 64, 52312 (2001).
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).
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.
The authors declare no competing financial interests.
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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
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