Experimental violation of a Bell-like causal inequality in a photonic quantum switch
Data files
Jun 17, 2026 version files 8.04 KB
-
Fig4_input_setting0000_vs_probability.csv
365 B
-
Fig4_input_setting0001_vs_probability.csv
361 B
-
Fig4_input_setting0010_vs_probability.csv
366 B
-
Fig4_input_setting0011_vs_probability.csv
361 B
-
Fig4_input_setting0100_vs_probability.csv
368 B
-
Fig4_input_setting0101_vs_probability.csv
367 B
-
Fig4_input_setting0110_vs_probability.csv
365 B
-
Fig4_input_setting0111_vs_probability.csv
371 B
-
Fig4_input_setting1000_vs_probability.csv
373 B
-
Fig4_input_setting1001_vs_probability.csv
374 B
-
Fig4_input_setting1010_vs_probability.csv
373 B
-
Fig4_input_setting1011_vs_probability.csv
374 B
-
Fig4_input_setting1100_vs_probability.csv
372 B
-
Fig4_input_setting1101_vs_probability.csv
374 B
-
Fig4_input_setting1110_vs_probability.csv
371 B
-
Fig4_input_setting1111_vs_probability.csv
373 B
-
README.md
2.13 KB
Abstract
Indefinite causal order can be realized by a quantum switch, yet its experimental certification has so far relied on assumptions about the devices. A device-independent verification of indefinite causal order would show, from the observed correlations alone and without relying on a detailed model of the devices, that they are incompatible with any classical description based on a fixed causal order. Here we implement a photonic quantum switch in a device-independent scenario and test a Bell-like causal inequality using entangled photons. One photon serves as the control qubit of the quantum switch, while the other is measured by a distant party with rapidly and independently chosen settings. We observe a violation of the causal inequality by 24 standard deviations. These results provide experimental evidence for indefinite causal order, albeit in the presence of remaining loopholes, and mark an important step toward a fully loophole-free device-independent verification of causal indefiniteness in quantum processes.
Dataset DOI: 10.5061/dryad.8kprr4z24
Description of the data and file structure
This dataset contains experimental results of the setting–outcome correlations generated by the quantum switch.
Files and variables
File: Fig4_input_setting0000_vs_probability.csv; Fig4_input_setting0001_vs_probability.csv;Fig4_input_setting0010_vs_probability.csv; Fig4_input_setting0011_vs_probability.csv; Fig4_input_setting0101_vs_probability.csv; Fig4_input_setting0110_vs_probability.csv; Fig4_input_setting0111_vs_probability.csv; Fig4_input_setting1000_vs_probability.csv; Fig4_input_setting1001_vs_probability.csv; Fig4_input_setting1010_vs_probability.csv; Fig4_input_setting1011_vs_probability.csv; Fig4_input_setting1100_vs_probability.csv; Fig4_input_setting1101_vs_probability.csv; Fig4_input_setting1110_vs_probability.csv; Fig4_input_setting1111_vs_probability.csv; Fig4_input_setting0100_vs_probability.csv
Description: These data files correspond to Fig. 4 of the manuscript “Experimental violation of a Bell-like causal inequality in a photonic quantum switch.” Fig. 4 shows the experimentally measured setting–outcome correlations generated by the quantum switch, together with the corresponding theoretical predictions. Each data file corresponds to one subpanel of Fig. 4 and represents the conditional probability distribution of the joint outcomes {a1, a2, b, c} for a given input setting {x1, x2, y, z}. In all data files, the first column represents the “outcome”, which corresponds to the horizontal axis of Fig. 4. The second and third columns represent the “probability” and “errorbar”, respectively, which correspond to the vertical-axis values and their experimental uncertainties in Fig. 4. The “input setting” labels the 16 different choices of {x1, x2, y, z}, corresponding to the 16 subpanels in Fig. 4. The experimental uncertainties arise from photon-counting statistics and correspond to standard deviations.
Code/software
Origin