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Article

Experimental simulation of closed timelike curves

  • Nature Communications 5, Article number: 4145 (2014)
  • doi:10.1038/ncomms5145
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Abstract

Closed timelike curves are among the most controversial features of modern physics. As legitimate solutions to Einstein’s field equations, they allow for time travel, which instinctively seems paradoxical. However, in the quantum regime these paradoxes can be resolved, leaving closed timelike curves consistent with relativity. The study of these systems therefore provides valuable insight into nonlinearities and the emergence of causal structures in quantum mechanics—essential for any formulation of a quantum theory of gravity. Here we experimentally simulate the nonlinear behaviour of a qubit interacting unitarily with an older version of itself, addressing some of the fascinating effects that arise in systems traversing a closed timelike curve. These include perfect discrimination of non-orthogonal states and, most intriguingly, the ability to distinguish nominally equivalent ways of preparing pure quantum states. Finally, we examine the dependence of these effects on the initial qubit state, the form of the unitary interaction and the influence of decoherence.

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Acknowledgements

We thank Nathan Walk and Nicolas Menicucci for insightful discussions. We acknowledge financial support from the ARC Centres of Excellence for Engineered Quantum Systems (CE110001013) and Quantum Computation and Communication Technology (CE110001027). A.G.W. and T.C.R. acknowledge support from a UQ Vice-Chancellor's Senior Research Fellowship.

Author information

Affiliations

  1. Centre for Engineered Quantum Systems, School of Mathematics and Physics, University of Queensland, Brisbane, QLD 4072, Australia

    • Martin Ringbauer
    • , Matthew A. Broome
    • , Casey R. Myers
    •  & Andrew G. White
  2. Centre for Quantum Computation and Communication Technology, School of Mathematics and Physics, University of Queensland, Brisbane, QLD 4072, Australia

    • Martin Ringbauer
    • , Matthew A. Broome
    • , Andrew G. White
    •  & Timothy C. Ralph

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Contributions

M.R., M.A.B., C.R.M. and T.C.R. developed the concepts, designed the experiment, analysed the results and wrote the paper. M.R. performed the experiments and analysed the data. T.C.R. and A.G.W. supervised the project and edited the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Martin Ringbauer.

Supplementary information

PDF files

  1. 1.

    Supplementary Information

    Supplementary Figures 1-2, Supplementary Notes 1-3 and Supplementary References

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