Bounding the speed of `spooky action at a distance' (1303.0614v2)

Abstract: In the well-known EPR paper, Einstein et al. called the nonlocal correlation in quantum entanglement as spooky action at a distance'. If the spooky action does exist, what is its speed? All previous experiments along this direction have locality loopholes and thus can be explained without having to invoke anyspooky action' at all. Here, we strictly closed the locality loopholes by observing a 12-hour continuous violation of Bell inequality and concluded that the lower bound speed of `spooky action' was four orders of magnitude of the speed of light if the Earth's speed in any inertial reference frame was less than 10^-3 times of the speed of light.

• The paper establishes a rigorous experimental test by closing both locality and freedom-of-choice loopholes with 16‐km distributed entangled photons.
• It reports a continuous 12‐hour violation of the Bell-CHSH inequality, setting a lower bound for nonlocal correlation speeds at four orders of magnitude above light speed.
• The study’s advanced tracking and synchronization methods pave the way for improved quantum communication systems and multi-party quantum networks.

An Examination of Quantum Nonlocal Correlations: Bounding the Speed of Spooky Action at a Distance

The paper "Bounding the speed of `spooky action at a distance'" addresses a central concern in quantum mechanics: the nature and speed of nonlocal correlations, colloquially termed by Einstein as 'spooky action at a distance'. This work seeks to empirically determine a lower bound for the velocity of such correlations, employing a meticulous approach that eliminates previously encountered loopholes in testing scenarios.

Experimental Approach

The paper leverages the theoretical framework laid out by Eberhard and the subsequent experimental advancements by Salart et al., aiming to conduct a stringent test that obviates both locality and freedom-of-choice loopholes. Entangled photon pairs were distributed over a 16-kilometer distance using a free-space optical link. The researchers employed fast electro-optic modulators to rigorously address the freedom-of-choice aspect, while a space-like Bell test was used to ensure closure of the locality loophole.

A distinguishing feature of this paper was the 12-hour continuous observation period, enabled by advanced laser tracking and synchronization methodologies. The use of laser-assisted tracking, combined with CMOS cameras and piezo-driven mirror systems, enabled maintenance of optical link stability over extended durations, with a desired timing accuracy better than 1 nanosecond.

Results

By implementing this meticulous configuration, the researchers achieved a continuous, 12-hour violation of the Bell-CHSH inequality. The derived lower bound for the speed of these nonlocal correlations was found to be four orders of magnitude greater than the speed of light ($c$), under the assumption that the Earth's center moves at less than $10^{-3}$ times the speed of light in any inertial frame. Even at a relativistic speed of $0.9c$ for the Earth's center, the calculated speed of 'spooky action' remains well above $c$, suggesting a universally applicable, non-classical characteristic of quantum mechanics.

Implications

The findings bolster the non-classical interpretation of entangled systems, indicating that the bounds of quantum correlations exceed the relativistic speed limit within tested frameworks. The empirical results further challenge causality constraints proposed by classical physics, affirming the persistently counter-intuitive nature of quantum mechanics.

In practical terms, the robust methodologies employed in this paper open avenues for future advancements in quantum communication technologies, including satellite-based quantum communication systems and multi-party quantum networks. The extensive tracking and synchronization systems developed could play crucial roles in enhancing the feasibility and reliability of such technologies.

Future Prospects

While this paper provides a rigorous lower bound for quantum correlation speeds, future investigations may focus on exploring these nonlocal correlations in varied multi-dimensional entangled systems to ascertain how many-party interactions might further nuance our understanding of quantum mechanics. Additionally, further enhancement of test methodologies, potentially involving more advanced quantum random number generators, could further solidify our understanding of the fundamental nature of the quantum world.

This comprehensive paper makes a substantial contribution to the field by refining our understanding of nonlocal quantum phenomena and providing a rigorous experimental protocol that may serve as a benchmark for future inquiries into the nature and implications of entangled quantum states.