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Here\u2019s what you\u2019ll learn when you read this story:<\/p>\n
In 1927, Albert Einstein and Neils Bohr debated the nature of what\u2019s known as complementarity\u2014the idea that a photon\u2019s dual wave-like and particle natures can\u2019t be measured at the same time.<\/p>\n
Now, two unrelated-but-similar experiments confirm that, in a double-slit experiment, detection of a photon\u2019s path (its particle nature) would wash out its interference pattern (its wave nature), proving Bohr right.<\/p>\n
Using these experimental set-ups could help scientists probe other questions of the quantum realm, including the nitty-gritty details of the interaction between decoherence and entanglement.<\/p>\n
The 1920s were an incredible time for science. The decade\u2014prefaced by the stunning confirmation of Albert Einstein<\/a>\u2019s General Theory of Relativity<\/a>, thanks to the solar eclipse in <\/a>May of 1919<\/a>\u2014saw the confirmation of the existence of other galaxies, the discovery of penicillin<\/a>, and the birth of modern quantum mechanics<\/a>. A complete banger of a decade, scientifically speaking.<\/p>\n However, this plethora of science knowledge came with some understandable disagreements. For example, it was becoming increasingly clear that Einstein<\/a>\u2019s elegant theories that appeared to govern the universe on a macro scale didn\u2019t perfectly square with the quantum weirdness being discovered at the subatomic scale. One of the most famous debates of the decade involved arguably two of the greatest physicists of the century: Einstein himself and Neils Bohr<\/a>, the world-famous Danish theoretical physicist who is a foundational figure in quantum mechanics<\/a>. The matter in question was the idea of \u201ccomplementarity,\u201d which stated (in simple terms) that a photon\u2019s particle and wave nature can\u2019t be measured at the same time.<\/p>\n Einstein believed that, by using a complicated double-slit experiment involving a spring that recoils when a photon enters, one could learn about that photon\u2019s particle nature based on which slit it entered and its wave nature based on the interference pattern. Bohr disagreed, stating that the quantum mechanical uncertainty principle essentially made this detection impossible.<\/p>\n Now, in two back-to-back experiments\u2014both published<\/a> in the journal Physical Review Letters<\/a>\u2014scientists at MIT and the University of Science and Technology of China (USTC) have seemingly settled the matter in favor of Bohr. Earlier this year, Wolfgang Ketterle (along with colleagues at MIT) created what the study authors call an \u201cidealized version of the double slit experiment,\u201d in which they used individual atoms as slits and weak beams of light so that those atoms scattered only one photon. Ketterle and his team essentially discovered an inverse relationship between the photon\u2019s two states: the more information that was obtained about the photon\u2019s path (i.e. particle nature), the lower the visibility of the interference pattern (i.e. wave nature).<\/p>\n The USTC experiment, which probes the same debate through different means, used a rubidium atom<\/a> held in place by optical tweezers. The team then used lasers and electromagnetic forces to control the atom\u2019s quantum properties and scattered light in two directions. They also found that Bohr\u2019s assertion held out.<\/p>\n \u201cSeeing quantum mechanics \u2018in action\u2019 at this fundamental level is simply breathtaking,\u201d Chao-Yang Lu told New Scientist<\/a>. \u201cBohr\u2019s counterargument was brilliant. But the thought experiment remained theoretical for almost a century.\u201d<\/p>\n