Assistant Professor Haocun Yu is something of a scientific diplomat. In a recent Physical Review Letters publication, she and her colleagues show how a tabletop experiment can bring together two bedrock physics theories that have never been fully reconciled.
More than a century ago, Albert Einstein gave us the theory of general relativity, describing gravity in relation to space and time on a large scale. Within a decade, physicists were developing a deeper knowledge of quantum mechanics, the laws that govern the subatomic world, including atoms, photons and other microscopic systems.
"Quantum mechanics and general relativity are two of the most successful theories in physics, but they describe nature in very different ways," Yu explained.
"To understand nature at its deepest level, we need experiments that probe where these two frameworks overlap. Studying gravitational effects in genuinely quantum systems can help reveal whether the two theories remain fully compatible in that regime, and it may point the way toward new physics."
She said the challenge in those studies is that, compared with other physical effects, gravity is "extraordinarily weak" at the scale of single quantum particles. This gives it an extremely small signature that's difficult to gauge.
To overcome that obstacle, she and her colleagues built a highly stable 50-kilometer (31-mile) optical interferometer using compact fiber coils and tested it with single photons. The entire apparatus can fit on a tabletop.
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