Letter

Experimental investigation of the no-signalling principle in parity–time symmetric theory using an open quantum system

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Abstract

The experimental progress achieved in parity–time () symmetry in classical optics1,2,3,4,5,6,7,8,9,10,11,12,13,14 is the most important accomplishment in the past decade15 and stimulates many new applications, such as unidirectional light transport5,6,7,8 and single-mode lasers12,13. However, in the quantum regime, some controversial effects are proposed for -symmetric theory16,17,18,19, for example, the potential violation of the no-signalling principle19. It is therefore important to understand whether -symmetric theory is consistent with well-established principles. Here, we experimentally study this no-signalling problem related to the -symmetric theory using two space-like separated entangled photons, with one of them passing through a post-selected quantum gate, which effectively simulates a -symmetric evolution. Our results suggest that the superluminal information transmission can be simulated when the successfully -symmetrically evolved subspace is solely considered. However, considering this subspace is only a part of the full Hermitian system, additional information regarding whether the -symmetric evolution is successful is necessary, which transmits to the receiver at maximally light speed, maintaining the no-signalling principle.

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Acknowledgements

We are grateful to C. J. Zhang, Y. C. Lee and D. C. Brody for valuable discussions. This work is supported by the National Natural Science Foundation of China (Grants numbers 61490711, 11474267, 11274289, 11304305, 11325419, 61327901 and 91321313), the Strategic Priority Research Program(B) of the Chinese Academy of Sciences (Grant No. XDB01030300). C-F.L. acknowledges support from the EU Collaborative project QuProCS (641277).

Author information

Author notes

    • Jian-Shun Tang
    •  & Yi-Tao Wang

    These authors contributed equally to this work

Affiliations

  1. Key Laboratory of Quantum Information, University of Science and Technology of China, Chinese Academy of Sciences, Hefei, Anhui 230026, China

    • Jian-Shun Tang
    • , Yi-Tao Wang
    • , Shang Yu
    • , De-Yong He
    • , Jin-Shi Xu
    • , Bi-Heng Liu
    • , Geng Chen
    • , Yong-Nan Sun
    • , Kai Sun
    • , Yong-Jian Han
    • , Chuan-Feng Li
    •  & Guang-Can Guo
  2. Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China

    • Jian-Shun Tang
    • , Yi-Tao Wang
    • , Shang Yu
    • , De-Yong He
    • , Jin-Shi Xu
    • , Bi-Heng Liu
    • , Geng Chen
    • , Yong-Nan Sun
    • , Kai Sun
    • , Yong-Jian Han
    • , Chuan-Feng Li
    •  & Guang-Can Guo

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Contributions

C-F.L., J-S.T., Y-T.W. and Y-J.H. planned and designed the experiments. J-S.T., Y-T.W. and S.Y. implemented the experiments with the help of J-S.X. and B-H.L. D-Y.H. fabricated the home-made circuit. C-F.L., Y-J.H., J-S.T., Y-T.W., G.C., Y-N.S. and K.S. carried out the theoretical analysis and developed the interpretation. J-S.T. and Y-J.H. wrote the paper with the help of C-F.L. and Y-T.W., and all authors discussed its contents. Y-J.H. supervised the theoretical part of the project. G-C.G. and C-F.L. supervised the project.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Yong-Jian Han or Chuan-Feng Li.

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