- The new technique of measuring gravity exploits the quantum nature of cold, trapped atoms.
- It is far more accurate than the standard technique which involves tracking free-falling atoms in a vertical chamber.
Usually, the gravity experiments are conducted by dropping things down in shielded tubes and measuring them as they whiz by instruments. For example, one can measure the influence of gravity on atoms by recording how fast atoms tumble down tall chutes.
These experiments help scientists determine various fundamental constants and test Einstein’s theory of gravity. However, vertical tubes used in free-fall experiments are hard to isolate from environmental interference like stray magnetic fields.
To overcome this issue and measure gravity in more detail, physicists at the University of California, Berkeley, have developed a new technique for measuring Earth’s gravity. Instead of tracking falling atoms, it exploits the quantum nature of trapped atoms to measure minute variations in the planet’s gravitational field.
How Does It Work?
When vertically separated groups of atoms or matter waves recombine, they generate an interference pattern. Since gravitational force acting on an object relies on altitude above the surface of the Earth (plus other parameters like nearby massive objects, and the local density of the Earth’s crust), two sets of atoms experience a bit different gravitational potential energies.
By analyzing this difference, researchers can precisely measure variations in Earth’s gravity.
In this study, researchers cooled a group of cesium atoms to 300 nanoKelvin and launched them in the upper direction within a small vacuum chamber. They then applied two laser beams to put atoms in two spatially separated quantum superposition states.
The atoms were trapped for approximately 20 seconds and then allowed to fall. At this point, the second laser pulses are applied to remerge and interfere with the atomic wave packets.
By measuring the difference in wave-particle duality (which is affected by gravity) between the paired atoms, researchers precisely measured the Earth’s gravity.
Design of a lattice interferometer, where laser beams suspend each atom in two spatially separated quantum superposition states, in the Earth’s gravity | Credit: Sarah Davis
This new method has two major advantage over the standard one that uses free-falling atoms:
- It is less sensitive to vibrational noise.
- It uses relatively smaller devices: the whole setup fits on a bench measuring 120 cm by 240 cm. The same experiment carried out on free-falling atoms would require a 500-meter tall vacuum system.
Moreover, a portable gravity measuring device can be built to employ this method. It will make it easy to measure Earth’s gravitational field in different locations and help identify mineral deposits. It might also prove helpful for physicists trying to understand the nature of dark matter and other mysterious phenomena.