Experimental violation of a Bell-like inequality for causal order
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arXiv
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| Auteurs principaux: | , , , , , , , |
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| Format: | Preprint |
| Publié: |
2025
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| _version_ | 1866918070028599296 |
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| author | Guo, Yu Tang, Hao Hu, Xiao-Min Huang, Yun-Feng Liu, Chuan-Feng Guo, Guang-Can Chiribella, Giulio Liu, Bi-Heng |
| author_facet | Guo, Yu Tang, Hao Hu, Xiao-Min Huang, Yun-Feng Liu, Chuan-Feng Guo, Guang-Can Chiribella, Giulio Liu, Bi-Heng |
| contents | Quantum mechanics allows for coherent control over the order in which different processes take place on a target system, giving rise to a new feature known as indefinite causal order. Indefinite causal order provides a resource for quantum information processing, and can be in principle be detected by the violation of certain inequalities on the correlations between measurement outcomes observed in the laboratory, in a similar way as quantum nonlocality can be detected by the violation of Bell inequalities. Here we report the experimental violation of a Bell-like inequality for causal order using a photonic setup where the order of two optical processes is controlled by a single photon of a polarization-entangled photon pair. Our proof-of-principle demonstration overcomes major technical challenges, including the need of high-speed quantum operations in photonic time-bin encoding, nanosecond synchronization of active optical and electronic elements to meet the target required for spacelike separation, and active temperature stabilization of a Mach-Zehnder interferometer to ensure statistically significant violations. These experimental advances enable a statistically significant violation of the causal inequality, and open up a path towards a device-independent certification of indefinite order of events with uncharacterized quantum devices. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2506_20516 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Experimental violation of a Bell-like inequality for causal order Guo, Yu Tang, Hao Hu, Xiao-Min Huang, Yun-Feng Liu, Chuan-Feng Guo, Guang-Can Chiribella, Giulio Liu, Bi-Heng Quantum Physics Optics Quantum mechanics allows for coherent control over the order in which different processes take place on a target system, giving rise to a new feature known as indefinite causal order. Indefinite causal order provides a resource for quantum information processing, and can be in principle be detected by the violation of certain inequalities on the correlations between measurement outcomes observed in the laboratory, in a similar way as quantum nonlocality can be detected by the violation of Bell inequalities. Here we report the experimental violation of a Bell-like inequality for causal order using a photonic setup where the order of two optical processes is controlled by a single photon of a polarization-entangled photon pair. Our proof-of-principle demonstration overcomes major technical challenges, including the need of high-speed quantum operations in photonic time-bin encoding, nanosecond synchronization of active optical and electronic elements to meet the target required for spacelike separation, and active temperature stabilization of a Mach-Zehnder interferometer to ensure statistically significant violations. These experimental advances enable a statistically significant violation of the causal inequality, and open up a path towards a device-independent certification of indefinite order of events with uncharacterized quantum devices. |
| title | Experimental violation of a Bell-like inequality for causal order |
| topic | Quantum Physics Optics |
| url | https://arxiv.org/abs/2506.20516 |