A quantum psychophysics perspective on bistable perception

Naïve and local realism

Death by experiment for local realism

Loophole-free Bell inequality violations

Bell inequality violations (Lecture slides)

The disjunctive theory of perception

The interface theory of perception

The evolution of perception (Video)

References

Gröblacher, S., Paterek, T., Kaltenbaek, R., Brukner, Č., Zukowski, M., Aspelmeyer, M., & Zeilinger, A.. (2007). An experimental test of non-local realism. Nature

“Most working scientists hold fast to the concept of ‘realism’ – a viewpoint according to which an external reality exists independent of observation. but quantum physics has shattered some of our cornerstone beliefs. according to bell’s theorem, any theory that is based on the joint assumption of realism and locality (meaning that local events cannot be affected by actions in space-like separated regions) is at variance with certain quantum predictions. experiments with entangled pairs of particles have amply confirmed these quantum predictions, thus rendering local realistic theories untenable. maintaining realism as a fundamental concept would therefore necessitate the introduction of ‘spooky’ actions that defy locality. here we show by both theory and experiment that a broad and rather reasonable class of such non-local realistic theories is incompatible with experimentally observable quantum correlations. in the experiment, we measure previously untested correlations between two entangled photons, and show that these correlations violate an inequality proposed by leggett for non-local realistic theories. our result suggests that giving up the concept of locality is not sufficient to be consistent with quantum experiments, unless certain intuitive features of realism are abandoned.”

Hensen, B., Bernien, H., Dreaú, A. E., Reiserer, A., Kalb, N., Blok, M. S., … Hanson, R.. (2015). Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometres. Nature

“For more than 80 years, the counterintuitive predictions of quantum theory have stimulated debate about the nature of reality. in his seminal work, john bell proved that no theory of nature that obeys locality and realism can reproduce all the predictions of quantum theory. bell showed that in any local realist theory the correlations between distant measurements satisfy an inequality and, moreover, that this inequality can be violated according to quantum theory. this provided a recipe for experimental tests of the fundamental principles underlying the laws of nature. in the past decades, numerous ingenious bell inequality tests have been reported. however, because of experimental limitations, all experiments to date required additional assumptions to obtain a contradiction with local realism, resulting in loopholes. here we report on a bell experiment that is free of any such additional assumption and thus directly tests the principles underlying bell’s inequality. we employ an event-ready scheme that enables the generation of high-fidelity entanglement between distant electron spins. efficient spin readout avoids the fair sampling assumption (detection loophole), while the use of fast random basis selection and readout combined with a spatial separation of 1.3 km ensure the required locality conditions. we perform 245 trials testing the chsh-bell inequality $s leq 2$ and find $s = 2.42 pm 0.20$. a null hypothesis test yields a probability of $p = 0.039$ that a local-realist model for space-like separated sites produces data with a violation at least as large as observed, even when allowing for memory in the devices. this result rules out large classes of local realist theories, and paves the way for implementing device-independent quantum-secure communication and randomness certification.”

Giustina, M., Versteegh, M. A. M., Wengerowsky, S., Handsteiner, J., Hochrainer, A., Phelan, K., … Zeilinger, A.. (2015). Significant-Loophole-Free Test of Bell’s Theorem with Entangled Photons. Physical Review Letters

“Local realism is the worldview in which physical properties of objects exist independently of measurement and where physical influences cannot travel faster than the speed of light. bell’s theorem states that this worldview is incompatible with the predictions of quantum mechanics, as is expressed in bell’s inequalities. previous experiments convincingly supported the quantum predictions. yet, every experiment requires assumptions that provide loopholes for a local realist explanation. here we report a bell test that closes the most significant of these loopholes simultaneously. using a well-optimized source of entangled photons, rapid setting generation, and highly efficient superconducting detectors, we observe a violation of a bell inequality with high statistical significance. the purely statistical probability of our results to occur under local realism does not exceed $3.74 times 10^{-31}$, corresponding to an 11.5 standard deviation effect.”

Scheidl, T., Ursin, R., Kofler, J., Ramelow, S., Ma, X.-S., Herbst, T., … Zeilinger, A.. (2010). Violation of local realism with freedom of choice. Proceedings of the National Academy of Sciences

“Bell’s theorem shows that local realistic theories place strong restrictions on observable correlations between different systems, giving rise to bell’s inequality which can be violated in experiments using entangled quantum states. bell’s theorem is based on the assumptions of realism, locality, and the freedom to choose between measurement settings. in experimental tests, ‘loopholes’ arise which allow observed violations to still be explained by local realistic theories. violating bell’s inequality while simultaneously closing all such loopholes is one of the most significant still open challenges in fundamental physics today. in this paper, we present an experiment that violates bell’s inequality while simultaneously closing the locality loophole and addressing the freedom-of-choice loophole, also closing the latter within a reasonable set of assumptions. we also explain that the locality and freedom-of-choice loopholes can be closed only within nondeterminism, i.e., in the context of stochastic local realism.”

Abellán, C., Acín, A., Alarcón, A., Alibart, O., Andersen, C. K., Andreoli, F., … Zhong, J.. (2018). Challenging local realism with human choices. Nature

“A bell test, which challenges the philosophical worldview of local realism against experimental observations, is a randomized trial requiring spatially-distributed entanglement, fast and high-efficiency detection, and unpredictable measurement settings. while technology can perfect the first two of these, and while technological randomness sources enable device-independent protocols based on bell inequality violation, challenging local realism using physical randomizers inevitably makes assumptions about the same physics one aims to test. bell himself noted this weakness of physical setting choices and argued that human free will could rigorously be used to assure unpredictability in bell tests. here we report a suite of local realism tests using human choices, avoiding assumptions about predictability in physics. we recruited ~100,000 human participants to play an online video game that incentivizes fast, sustained input of unpredictable bits while also illustrating bell test methodology. the participants generated 97,347,490 binary choices, which were directed via a scalable web platform to twelve laboratories on five continents, in which 13 experiments tested local realism using photons, single atoms, atomic ensembles, and superconducting devices. over a 12-hour period on the 30 nov. 2016, participants worldwide provided a sustained flow of over 1000 bits/s to the experiments, which used different human-generated bits to choose each measurement setting. the observed correlations strongly contradict local realism and other realist positions in bi-partite and tri-partite scenarios. project outcomes include closing of the freedom-of-choice loophole, gamification of statistical and quantum non-locality concepts, new methods for quantum-secured communications, a very large dataset of human-generated randomness, and networking techniques for global participation in experimental science.”

Wiseman, H.. (2015). Quantum physics: Death by experiment for local realism. Nature

“The world is made up of real stuff, existing in space and changing only through local interactions — this local-realism hypothesis is about the most intuitive scientific postulate imaginable. but quantum mechanics implies that it is false, as has been known for more than 50 years1. however, brilliantly successful though quantum mechanics has been, it is still only a theory, and no definitive experiment has disproved the local-realism hypothesis — until now. on page 682 of this issue [doi: 10.1038/nature15759], hensen et al.2 report the first violation of a constraint called a bell inequality, under conditions that prevent alternative explanations of the experimental data. their findings therefore rigorously reject local realism, for the first time… a bell inequality is a mathematical relationship regarding the statistics of measurement outcomes obtained by two or more parties. under certain physical conditions relating to the timing of events, a violation of a bell inequality proves that local realism — a hypothesis satisfied in all of science except quantum mechanics — is false.”

Zhao, Z., Yang, T., Chen, Y. A., Zhang, A. N., Żukowski, M., & Pan, J. W.. (2003). Experimental violation of local realism by four-photon greenberger-horne-zeilinger entanglement. Physical Review Letters

“We report the first experimental violation of local realism in four-photon greenberger-horne-zeilinger (ghz) entanglement. in the experiment, the non-statistical ghz conflicts between quantum mechanics and local realism are confirmed, within the experimental accuracy, by four specific measurements of polarization correlations between four photons. in addition, our experimental results not only demonstrate a violation of mermin-ardehali-belinskii-klyshko inequality by 76 standard deviations, but also for the first time provide sufficient evidence to confirm the existence of genuine four-particle entanglement.”