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Experimental test of local observer-independence (1902.05080v2)

Published 13 Feb 2019 in quant-ph

Abstract: The scientific method relies on facts, established through repeated measurements and agreed upon universally, independently of who observed them. In quantum mechanics, the objectivity of observations is not so clear, most dramatically exposed in Eugene Wigner's eponymous thought experiment where two observers can experience seemingly different realities. The question whether these realities can be reconciled in an observer-independent way has long remained inaccessible to empirical investigation, until recent no-go-theorems constructed an extended Wigner's friend scenario with four observers that allows us to put it to the test. In a state-of-the-art 6-photon experiment, we realise this extended Wigner's friend scenario, experimentally violating the associated Bell-type inequality by 5 standard deviations. If one holds fast to the assumptions of locality and free-choice, this result implies that quantum theory should be interpreted in an observer-dependent way.

Citations (103)

Summary

  • The paper demonstrates experimental violation of a Bell-type inequality by five standard deviations, challenging the assumption of observer-independence in quantum mechanics.
  • It employs an advanced 6-photon interferometric setup extending Wigner's friend scenario to reveal dual observational perspectives in quantum systems.
  • The findings prompt significant implications for quantum theory interpretations and practical applications in quantum computing and cryptography.

Analysis of Observer-Independence in Quantum Mechanics: Empirical Evaluation

The paper, "Experimental test of local observer-independence," presents a meticulous exploration of the observer-dependence in quantum mechanics, as philosophically characterized by Wigner's thought experiment. Here, the authors endeavor to empirically assess whether quantum reality is objective—observer-independent—or subjective, reliant on observers' perspectives. Using an elaborate experimental setup involving photonic systems, the research examines the classical presumption that multiple observers can coherently perceive a unified version of reality.

Experimental Methodology

The experiment leverages a state-of-the-art 6-photon interferometric setup to implement an extended Wigner’s friend scenario. At its core, Wigner's thought experiment illustrates a dual reality: an observer within a system records a definite outcome, while an outside observer describes the system in superposition. A sophisticated entangled 6-photon state is employed corporatively with Bell-type inequality measurements among dual observation setups—each encapsulating an observer and a subordinate 'friend.'

Results and Implications

The experiment notably violates a Bell-type inequality by five standard deviations, constraining the assumption known as observer-independence, fundamental to realism. This inequality tests assumptions such as locality and free choice, convergent to classic Bell scenarios but specifically interrogating the observer-independence assumption.

What unfolds from this empirical violation is the assertion that reality, under quantum mechanics, must accommodate observer-dependence if locality and free choice are conserved. This finding implies that quantum mechanics might necessitate an interpretation framework in which distinct observers' accounts cannot be universally reconciled.

Theoretical and Practical Relevance

The results prompt significant implications for quantum theory interpretation. Various interpretations, including Everett's many-worlds interpretation and Bohmian Mechanics, propose resolution strategies albeit within complex frameworks where observations are perpetually relative rather than absolute. Practically, accepting observer-dependent interpretations may lead to deviations in how quantum systems are modeled in computing and information theory, impacting fields like quantum cryptography reliant on fixed observer states.

Future Directions

Despite the experiment's proficiency, resolving the conclusiveness of observer-indepenence remains an open topic due to experimental constraints such as loss and detection efficiency—a few inevitable loopholes parallel to those in standard Bell tests. Future research might incorporate sophisticated error management and measurement verification techniques to affirm their findings across differing scales or contexts.

Conclusion

This paper offers a comprehensive empirical foundation questioning one of quantum mechanics’ pivotal assumptions: observer-independence. While it renders a significant step toward understanding observer dependence through experimentally driven insights, further explorations are necessitated to fully abstract these findings into practical frameworks and theoretical constructs that govern natural reality. The research could ultimately pave the way for novel theoretical developments and discussions within the quantum mechanics community regarding the facets of reality perception and observer role centrality to phenomena prediction and understanding.

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