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arXiv · 2608.28190

Postselection-loophole-free Bell test under strict spacetime constraints

Kannan Vijayadharan·Matías Rubén Bolaños·Andrea Pompermaier·Tommaso Bertapelle·Francesco B. L. Santagiustina·Costantino Agnesi·Giuseppe Vallone·Paolo Villoresi
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Abstract

Entanglement gives rise to correlations between distant quantum systems that cannot be explained by local realistic theories. Bell inequality violations provide a direct way to reveal these correlations and certify nonlocality, especially when the relevant experimental loopholes are closed. Time-bin encoding, in which quantum information is encoded into well-defined temporal modes, is a commonly used platform for distributing photonic entanglement in optical fibers. Yet loophole-free Bell tests with time-bin entanglement have received comparatively little attention, owing in part to the postselection loophole introduced by conventional interferometric measurements. Here, we demonstrate a fiber-based platform for Bell tests with time-bin entanglement that simultaneously closes the locality, freedom-of-choice, and postselection loopholes. We observe a CHSH violation of $S=2.583 \pm 0.002$, exceeding the local-realistic bound by over 265 standard deviations. Notably, this rigorous certification of nonlocality is achieved at a separation distance of $49.0 \pm 0.7$ m, substantially shorter than previous photonic Bell tests addressing comparable space-time constraints. Beyond its foundational significance, our results demonstrate time-bin entanglement as a viable route towards practical device-independent quantum communication and a future quantum internet.

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Kannan Vijayadharan, Matías Rubén Bolaños, Andrea Pompermaier, Tommaso Bertapelle, Francesco B. L. Santagiustina, Costantino Agnesi, Giuseppe Vallone, Paolo Villoresi. 2026-08-28. Postselection-loophole-free Bell test under strict spacetime constraints. https://arxiv.org/abs/2608.28190

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