Physicists at UC Berkeley immobilized small clusters of cesium atoms in a vertical vacuum chamber, then split each atom into a quantum state in which half of the atom was closer to a tungsten weight than the other half . By measuring the phase difference between the two halves of the atomic wave function, they were able to calculate the difference in the gravitational attraction between the two parts of the atom, which matched what is expected from Newtonian gravity.
The experiment, which combines an atom interferometer for precise gravity measurements with an optical lattice to hold the atoms in place, allowed the researchers to immobilize free-falling atoms for seconds instead of milliseconds to look for gravitational effects, besting the current most precise measurement by a factor of five.
“Most theorists probably agree that gravity is quantum. But nobody has ever seen an experimental signature of that,” Müller said. “It’s very hard to even know whether gravity is quantum, but if we could hold our atoms 20 or 30 times longer than anyone else, because our sensitivity increases with the second or fourth power of the hold time, we could have a 400 to 800,000 times better chance of finding experimental proof that gravity is indeed quantum mechanical.
Because the optical lattice holds atoms rigidly in place, the lattice atom interferometer could even operate at sea, where sensitive gravity measurements are employed to map the geology of the ocean floor.Dark energy was discovered in 1998 by two teams of scientists: a group of physicists based at Lawrence Berkeley National Laboratory, led by Saul Perlmutter, now a UC Berkeley professor of physics, and a group of astronomers that included UC Berkeley postdoctoral fellow Adam Riess.
One theory is that dark energy is merely the vacuum energy of space. Another is that it is an energy field called quintessence, which varies over time and space. “Atom interferometry is the art and science of using the quantum properties of a particle, that is, the fact that it’s both a particle and a wave. We split the wave up so that the particle is taking two paths at the same time and then interfere them at the end,” Müller said. “The waves can either be in phase and add up, or the waves can be out of phase and cancel each other out.