Gravity on a Chip...

Diagram showing how a BEC (red dot) is created at the top of the chip. It then falls and is split into two BECs that take separate paths to the bottom of the chip. (Courtesy: S Abend/Phys. Rev. Lett.)

Topics: Bose-Einstein Condensate, Gravity, Nanotechnology, Quantum Mechanics, Semiconductor Technology

A new sensor that measures the local acceleration due to gravity using a Bose–Einstein condensate (BEC) of ultracold atoms has been made by physicists in Germany, the US and Canada. While the prototype device is not as accurate as commercial gravimeters, its makers say it could be made much smaller and much more accurate than existing devices.

Atoms can be used to measure the acceleration due to gravity by cooling a gas of them to near absolute zero and then dropping them along two different paths in an interferometer. The quantum interference that occurs when the paths converge at a detector provides a very good measure of gravity, with commercial atom interferometers able to measure the acceleration to within one part in 108. Such measurements are invaluable for geological exploration because the presence of certain minerals can be spotted by seeking tiny variations in gravity at the Earth's surface.

While these ultracold atom gravimeters are on a par with conventional absolute gravimeters based on macroscopic falling masses, their accuracy could be improved a lot by using a BEC. In a conventional atomic gravimeter, the ultracold atoms form a diffuse gas roughly a millimetre in size and a major cause of uncertainty is that the laser pulses used to control the atoms are not spatially uniform on that length scale. A BEC – formed by cooling a gas of atoms with integer spin until they condense into a single quantum state – reduces this uncertainty because it squeezes the atoms into a region that is about 100 times smaller.

Physics World: Gravity measured using a Bose–Einstein condensate on a chip
Hamish Johnston