A high degree of precision in measuring gravity comes in useful in many contexts — from minute measurements of plate tectonics and seismology to searching for minerals underground. Gravimeters, which are used for this purpose, are often bulky.
Now, scientists from Germany, Canada and the U.S. have demonstrated an atom-chip, quantum device which paves the way to developing gravimeters that can fit into a backpack.
Also, the newly proposed device would improve by a factor of ten the accuracy of measurement attributed to currently available gravimeters.
The research has been reported recently in Physical Review Letters.
The device uses a cloud of ultracold atoms which are trapped in a centimetre-size chip using lasers and magnets.
This cloud of atoms is allowed to fall and, using lasers, is split into two and routed through different paths. When the two parts recombine, the interference pattern gives a measure of the gravitational field on them.
Using atomic interferometry to measure gravity is not new and has been around for a while. In this method, atoms are cooled to a temperature near absolute zero when their quantum nature is dominant.
They are then made to traverse different paths using lasers, and the interference pattern is observed. Measurements using this process can be made more precise if the atoms are first squeezed together to form a so-called Bose-Einstein condensate .
Bose Einstein condensateThis is a state of matter where all the atoms of the substance occupy the same quantum level – in other words, they coalesce into a blob and can be described by a single wave function.
Using a Bose-Einstein Condensate (BEC) instead of independent atoms contributes to the aim of miniaturisation – the BEC has a diameter which is about a hundred times smaller than a non-BEC atom cloud.
The BEC atoms are trapped near the surface of a chip using atom-chip technology.
Using lasers and magnetic fields, about 10,000 atoms are compressed to form the condensate, within about 15 seconds, which lies just below the surface of the centimetre-sized chip.
The laser is then made to “kick” the BEC and it connects with a fifty per cent probability. This results in the cloud being split, and a part of it is kicked and shoots up while the other falls without feeling the kick. The two pieces are made to follow slightly different paths, with the part that was kicked having followed a longer path.
When they eventually meet and interfere, they give a measure of the gravitational field. The researchers suggest that further miniaturisation should be possible with some modifications and that this demonstration will pave the way for small high-precision backpack-sized gravimeters to help in geodetic earth observation and exploration.
