Physicists combined an optical lattice with an atom interferometer to hold atoms in place for up to 70 seconds -- a record for an atom interferometer -- allowing them to more precisely test for deviations from the accepted theory of gravity that could be caused by dark energy particles such as chameleons or symmetrons. Though they detected no anomalies, they're improving the experiment to perform more sensitive tests of gravity, including whether gravity is quantized.
The ability of the lattice atom interferometer to hold atoms for up to 70 seconds -- and potentially 10 times longer -- also opens up the possibility of probing gravity at the quantum level, said Holger Müller, UC Berkeley professor of physics. While physicists have well-tested theories describing the quantum nature of three of the four forces of nature -- electromagnetism and the strong and weak forces -- the quantum nature of gravity has never been demonstrated.
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.
The key to using free-falling atoms to test gravity is the ability to excite each atom into a quantum superposition of two states, each with a slightly different momentum that carries them different distances from a heavy tungsten weight hanging overhead. The higher momentum, higher elevation state experiences more gravitational attraction to the tungsten, changing its phase.
"Gravity is trying to push them down with a force a billion times stronger than their attraction to the tungsten mass, but you have the restoring force from the optical lattice that's holding them, kind of like a shelf," Panda said."We then take each atom and split it into two wave packets, so now it's in a superposition of two heights.