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In a world first, scientists have experimentally verified the entanglement of the momentum of atoms, a feat previously only achieved with photons.<\/p>\n
Scientists from Australia and the U.S. pulled off this immensely tricky measurement using ultracold helium atoms and an immensely complicated set-up known as a Rarity-Tapster Interferometer.<\/p>\n
Because atoms have mass (unlike photons), this discovery opens up a door to studying gravitational effects in the quantum realm.<\/p>\n
The universe\u2014at least, as we know it\u2014appears to be governed by two overarching principles. In the world of celestial mechanics, Albert Einstein\u2019s General Theory of Relativity<\/a> explains the relationship between mass and energy, and in the realm of the subatomic, quantum mechanics run the show. For nearly a century, however, there\u2019s been a pretty big problem with this universal formulation\u2014the two theories don\u2019t really mesh.<\/p>\n One of the key sticking points is gravity<\/a>\u2014Einstein argues that it is an effect caused by the curvature of spacetime, while quantum physicists hypothesize that a (currently theoretical) force carrier known as a graviton<\/a> mediates gravitational interaction. For nearly a century, scientists have tried to find evidence that might knit these two grand theories together, but so far, a happy marriage has remained impossible.<\/p>\n Now, a new study conducted by scientists at the Australian National University (ANU) in Canberra, the University of Queensland, and the University of Oklahoma has, for the first time, experimentally confirmed that the momentum of atoms<\/a> can be entangled. While scientists have known about the entanglement of atoms (and the entanglement of photon momentum) for decades, this first confirmation of atom momentum entanglement is crucial to our understanding of the phenomenon\u2014largely because atoms contain mass, and can thus provide a way for scientists to study quantum effects and gravitational forces in the same experiment. The results of the study were published in the journal Nature Communications<\/a>.<\/p>\n \u201cThey show nonlocality in the external motion of atoms, rather than internal degrees of freedom such as spin,\u201d Yogesh Sridhar, lead author of the study and a Ph.D. student from ANU, said in a press statement<\/a>. \u201cThese results strengthen our confidence and understanding in quantum theory and also pave the way to testing quantum mechanical theories with even larger real-world objects.\u201d<\/p>\n For the experiment, Sridhar, lead researcher Sean Hodgman (also from ANU), and the rest of the team used three clouds of cold helium<\/a> atoms suspended in a magnetic trap. Once the magnets were turned off, the atoms fell under the influence of gravity and passed a series of grating laser pulses that created different paths along which the atoms could travel with equal probability. This set-up is what\u2019s known as a Rarity-Tapster Interferometer (a specifically designed optical device for measuring non-locality, or entanglement) within what\u2019s known as a Bell inequality-test framework<\/a> (which tests for the non-local nature of particles, as opposed to Einstein\u2019s local realism).<\/p>\n \u201cFor two separated atoms that are entangled, if you change one of them, it will instantly affect the other,\u201d Hodgman said in a press statement. \u201cIt\u2019s kind of crazy to think that this is how the world works, but we\u2019ve shown that it\u2019s the nature of reality<\/a>.\u201d<\/p>\n Of course, it\u2019s been long hypothesized that matter can be at multiple places at once\u2014at least, in a sense\u2014and still interact with itself over large distances (Einstein once famously described this concept as \u201cspooky action a distance<\/a>\u201d). But scientists have only been able to test that hypothesis in recent years because of advances in methods for controlling and measuring individual atoms.<\/p>\n