The second goal of iSense is to demonstrate the new technology platform by realising an ultracold-atom-based instrument able to measure the gravitational field with a precision comparable to the best commercial instrument, but in a more compact and portable format.
Measuring the gravitational field at the surface of the earth helps us to figure out what lies underground. Gravity sensors are useful tools for geodesy (e.g. ocean circulation, water balances, Antarctic ice levels, magma flows, etc), in the exploration of resources (location of scarce minerals, oil fields, etc) and archaeology (non-destructive mapping of sites and location of intact caverns). However, they tend to be rare and hard to use. By making gravity sensors more robust and portable, iSense will make gravity mapping more mainstream and open up new opportunities.
The iSense gravimeter will be able to measure g, the acceleration due to gravity (9.8m/s2 at the surface of the Earth) with a precision of 9 digits. This level of accuracy is comparable to the best commercially available instruments, which are still rather cumbersome and hard to operate.
As part of the design of the gravimeter, iSense seeks fundamental progress on the operating principles of the atom interferometer themselves. The natural way of measuring gravity is to let the atoms fall and measure how quickly they are accelerated. This approach has been very successful in the laboratory, but it requires an extended vacuum chamber to accommodate the free fall. It is therefore less compatible with a compact design.
On the other hand, holding the atoms in place is very likely to disturb the measurement. This is because the atom interferometer will be sensitive to all the forces felt by the atoms, including the force used to hold them in position! The iSense project develops cutting-edge new interferometric schemes that will maintain the position of the atoms while using them to measure an external influence, such as gravity or the electromagnetic forces close to a surface.