Cosmic Bell Test using Random Measurement Settings from High-Redshift Quasars (1808.05966v1)

Abstract: In this Letter, we present a cosmic Bell experiment with polarization-entangled photons, in which measurement settings were determined based on real-time measurements of the wavelength of photons from high-redshift quasars, whose light was emitted billions of years ago, the experiment simultaneously ensures locality. Assuming fair sampling for all detected photons and that the wavelength of the quasar photons had not been selectively altered or previewed between emission and detection, we observe statistically significant violation of Bell's inequality by $9.3$ standard deviations, corresponding to an estimated $p$ value of $\lesssim 7.4 \times 10^{-21}$. This experiment pushes back to at least $\sim 7.8$ Gyr ago the most recent time by which any local-realist influences could have exploited the "freedom-of-choice" loophole to engineer the observed Bell violation, excluding any such mechanism from $96\%$ of the space-time volume of the past light cone of our experiment, extending from the big bang to today.

Cosmic Bell Test Using High-Redshift Quasars

The paper "Cosmic Bell Test using Random Measurement Settings from High-Redshift Quasars" presents a significant advancement in empirical tests of quantum mechanics and local realism through utilizing entangled photons. In this experiment, photon measurement settings were determined based on real-time observations from quasars emitting light billions of years ago. The primary objective was to push the boundaries on the "freedom-of-choice" loophole, addressing potential local-realist influences.

Key Findings & Experimental Methodology

The authors executed a cosmic Bell experiment wherein measurement settings were triggered by cosmic photons observed at the Telescopio Nazionale Galileo (TNG) and the William Herschel Telescope (WHT). These quasars emitted light more than 7.8 billion years ago and were selected for their high redshift values, extending the constraints on conceivable local-realist loopholes to extremely distant cosmic history.

The experimental setup involved a centralized entangled photon source positioned between Alice's and Bob's stations, both equipped with telescopes to gather quasar light for random measurement settings. The telescopes filtered incoming photons using dichroic mirrors, categorizing them by wavelength into 'red' and 'blue' channels, with the settings for polarization measurements adapted based on these channels. The locality conditions were strictly maintained to prevent any feasible signaling between the sites within the confines of their light cones and entangled photon pathways.

Statistical analysis demonstrated that the experimental outcomes significantly contradicted Bell's inequality by 9.3 standard deviations with a p-value of $7.4 \times 10^{-21}$. This deviation affirms quantum mechanics against local realism assumptions, emphasizing the experiment's robustness in addressing the freedom-of-choice loophole deeply into cosmic history.

Implications for Quantum Mechanics

The implications of this research are profound both for practical quantum technologies and theoretical quantum mechanics. From a practical standpoint, ensuring high confidence in quantum mechanical interpretations bolsters reliability in quantum computing and quantum cryptography applications. Theoretically, it pushes our understanding of quantum entanglement, supporting non-local correlations over vast cosmic timelines and questioning the possible influences of pre-existing conditions at quantum scales. Further, these findings align with quantum mechanics assumptions regarding entangled systems, underpinning the non-classical correlations between spatially separated particles.

The experiment demonstrated how any potential local-realist mechanisms would necessitate influence extending at least 7.8 billion years into the cosmic past, thus significantly narrowing the space-time regions where classical compatibilities might exist. A pivotal aspect of this research lies in its exploration of far-reaching sources for randomness, implying future tests could consider electromagnetic radiation like cosmic microwave background radiation for even earlier constraints.

Speculative Future Directions

Future development in cosmic-scale Bell tests might leverage different cosmological signals, such as primordial neutrinos or gravitational waves, extending constraints potentially near the big bang or into early universe phenomena like inflationary cosmology. Additionally, these directions might eventually interface with emerging hypotheses relating to quantum entanglement and the construction of space-time fabric, merging fields of quantum mechanics and cosmological studies.