Cosmic Bell Test: Measurement Settings from Milky Way Stars

Abstract: Bell's theorem states that some predictions of quantum mechanics cannot be reproduced by a local-realist theory. That conflict is expressed by Bell's inequality, which is usually derived under the assumption that there are no statistical correlations between the choices of measurement settings and anything else that can causally affect the measurement outcomes. In previous experiments, this "freedom of choice" was addressed by ensuring that selection of measurement settings via conventional "quantum random number generators" was space-like separated from the entangled particle creation. This, however, left open the possibility that an unknown cause affected both the setting choices and measurement outcomes as recently as mere microseconds before each experimental trial. Here we report on a new experimental test of Bell's inequality that, for the first time, uses distant astronomical sources as "cosmic setting generators." In our tests with polarization-entangled photons, measurement settings were chosen using real-time observations of Milky Way stars while simultaneously ensuring locality. Assuming fair sampling for all detected photons, and that each stellar photon's color was set at emission, we observe statistically significant $\gtrsim 7.31 \sigma$ and $\gtrsim 11.93 \sigma$ violations of Bell's inequality with estimated $p$-values of $ \lesssim 1.8 \times 10^{-13}$ and $\lesssim 4.0 \times 10^{-33}$, respectively, thereby pushing back by $\sim$600 years the most recent time by which any local-realist influences could have engineered the observed Bell violation.

Overview of "Cosmic Bell Test: Measurement Settings from Milky Way Stars"

The paper entitled "Cosmic Bell Test: Measurement Settings from Milky Way Stars" makes a significant contribution to the experimental testing of Bell's inequalities by integrating astrophysical phenomena into the methodology of quantum entanglement tests. Bell's theorem postulates that the predictions of quantum mechanics are incompatible with local realism, which can be tested using Bell inequalities. These tests traditionally rely on ensuring that the choice of measurement settings is independent of any variables that could influence the measurement outcomes, known as the "freedom of choice" assumption.

Experimental Implementation

In this novel approach, the settings for measuring quantum entanglement were determined using real-time observations of photons emitted by distant stars in the Milky Way. This was done to close the "freedom-of-choice" loophole by extending the possible causal origins of measurement settings beyond those achievable with standard laboratory equipment. The experiment involved generating polarization-entangled photons, measured by two remote observers, Alice and Bob. The positions of the observers and their astronomical photon detection stations were chosen so that any signals from the stars (in the form of photon color choices) were space-like separated from the entangled photon measurement events.

Results and Implications

The results displayed strong violations of Bell's inequality, with the test yielding violations with statistical significance up to 11.93 standard deviations and p-values as low as (4.0 \times 10^{-33}). Assuming that the stellar photons' colors were determined at emission and had traveled undisturbed across the cosmos to be detected on Earth, any local-realist influences would have had to originate roughly 600 years ago. This temporal boundary pushes back the point at which any local hidden variables could influence the randomness typically employed in Bell tests, dramatically extending it beyond the conventional microsecond scale addressed by previous experiments.

This study opens the pathway for future cosmic Bell tests using even more distant astrophysical objects, such as quasars. The integration of astronomical sources into quantum tests represents a move toward closing one of the last remaining loopholes in experimental tests of quantum entanglement, providing insights into both foundational physics and potential applications in quantum information science.

Conclusion

The findings imply that any model relying on local hidden variables would have to contrive influences from distant and historical cosmic events, an unlikely scenario under current physics understanding. Moreover, the results underscore the robustness of quantum mechanics against local realism predictive measures, confirming the non-local nature of quantum correlations over extended space-time intervals. Future research may build upon this experimental framework to further explore the origins of quantum-entangled measurement settings within the cosmic scale and deepen our understanding of the fundamental nature of reality.