Gravitational Decoherence (1706.05677v2)

Abstract: We discuss effects of loss of coherence in low energy quantum systems caused by or related to gravitation, referred to as gravitational decoherence. These effects, resulting from random metric fluctuations, for instance, promise to be accessible by relatively inexpensive table-top experiments, way before the scales where true quantum gravity effects become important. Therefore, they can provide a first experimental view on gravity in the quantum regime. We will survey models of decoherence induced both by classical and quantum gravitational fluctuations; it will be manifest that a clear understanding of gravitational decoherence is still lacking. Next we will review models where quantum theory is modified, under the assumption that gravity causes the collapse of the wave functions, when systems are large enough. These models challenge the quantum-gravity interplay, and can be tested experimentally. In the last part we have a look at the state of the art of experimental research. We will review efforts aiming at more and more accurate measurements of gravity (G and g) and ideas for measuring conventional and unconventional gravity effects on nonrelativistic quantum systems.

Gravitational Decoherence: A Review

The paper under review provides a comprehensive examination of gravitational decoherence, exploring both its theoretical underpinnings and the potential for experimental verification. Authored by Angelo Bassi, André Großardt, and Hendrik Ulbricht, it navigates the complex terrain where general relativity and quantum mechanics intersect, particularly focusing on decoherence effects caused by gravitational influences on low-energy quantum systems.

Overview of Theoretical Frameworks

The authors first address gravitational decoherence through the lens of both classical and quantum gravitational fluctuations, noting the absence of a universally accepted theoretical framework. They emphasize the inherent challenges in modeling the interaction of quantum systems with a gravitational field, especially given that gravity has not been conclusively demonstrated to possess a quantum nature.

Classical approaches frequently employ stochastic perturbations of spacetime metrics to account for gravitational influences, which can manifest as noise-induced decoherence in quantum systems. These models often postulate a background spacetime that fluctuates due to gravitational waves or primordial cosmic phenomena.

The quantum perspective suggests decoherence as a consequence of graviton fields interacting with matter. However, the hypothesis of perturbative quantum gravity remains contentious and lacks empirical support. Proposed decoherence mechanisms stemming from quantum gravitational fields involve advanced mathematical treatments but remain speculative due to the absence of experimental verification at present.

Experimental Considerations

This paper does not shy away from discussing the experimental verification challenges of gravitational decoherence theories. It highlights how advancements in technology, particularly in table-top experiments, are poised to probe gravitational interactions in quantum regimes, potentially far from the elusive Planck scale.

Experiments involving matter-wave interferometers, superposition states, and advanced measurement techniques could open pathways to test hypotheses about gravitational decoherence. Moreover, experiments designed to measure minute gravitational influences could shed light on classical versus quantum interpretations of gravity's role in decoherence.

Implications and Future Directions

The implications of gravitational decoherence extend both practically and theoretically. Practically, understanding decoherence mechanisms is crucial for the development of stable quantum technologies, especially in fields such as quantum computation and precision measurement. Theoretically, the research challenges prevailing paradigms that treat gravity and quantum mechanics as disparate entities, urging a unified approach to understanding their interplay.

One noteworthy proposition in the paper is the examination of gravity-induced collapse models, which postulate that gravity might provide a mechanism for the collapse of quantum superposition states—a concept that stands in contrast to the often-assumed quantum nature of gravity.

Additionally, the discussion of semi-classical models, such as the Schrödinger-Newton equation, underscores a potentially radical shift from efforts to quantize gravity to those modifying quantum mechanics itself to account for gravitational effects. Such models provide testable predictions that can be explored with current or near-future experimental capabilities.

Conclusion

This paper is a significant contribution to the existing discourse on gravitational decoherence, providing a detailed examination of both theoretical formulations and experimental strategies. It underscores the complexity of unifying quantum mechanics and general relativity while positing feasible avenues for future research. The dialogue between theory and experiment is crucial, positioning gravitational decoherence as a pivotal area in the broader quest to comprehend the fabric of our universe.

In sum, the investigation of gravitational decoherence is not solely an academic endeavor; rather, it is a frontier that holds the potential to redefine our understanding of the foundational principles governing the cosmos.