Context: Ultracold atom experiments
Ultracold atoms are a relatively new field of physics which took off with the realisation that it was possible to cool down and trap a cloud of atoms with carefully adjusted laser beams and a magnetic field (a so-called magneto-optical trap). The discovery of laser cooling and of further refinements in the cooling methods led to the award of the Nobel prizes in 1997 and in 2001 .
In a magneto-optical trap, the temperature can be as low as 10 μK, that is to say barely 10 millionths of a degree above absolute zero! At this temperature, atoms in the gas move at a velocity of a few centimetres per second, compared to hundreds of meters per second in a gas at room temperature.
At these extremely low temperatures, quantum mechanics rules the world and atoms are better described by waves than by particles. Physicists have learned how to use the strange quantum behaviour to make things that are otherwise impossible in the classical world.
There are many reasons why ultracold atoms are useful when performing incredibly precise measurements:
- Atoms are perfect and are rigorously identical. This is not the case for manufactured objects. Therefore a measuring device relying on a manufactured artefact, such as a ruler to measure distances, or a pendulum to measure time, will always have a precision limited by manufacturing tolerances. This is not the case for single atoms.
- When being used to perform a sensitive measurement, an atom should remain at the position where the measurement is being made for a sufficient amount of time. Ultracold atoms move very slowly and are therefore well suited for the task.
- At low temperature, atoms behave like waves (they are described by a quantum mechanical wave function). We can use these matter waves in an atom interferometer the same way light is used in a conventional interferometer.
In the laboratory, atom interferometers have been successfully used to measure time (atomic clocks), accelerations (accelerometers, gyroscopes and gravimeters), and electromagnetic fields very close to surfaces. These experiments are usually world-class in the precision they reach.
A typical ultracold atom experiment is complex enough to fill a room. It is composed of a vacuum chamber that contains the gas of ultracold atoms, a number of lasers with their stabilisation optics and electronics, electromagnets to create magnetic fields and an optical table to hold all this equipment. It also consumes a lot of energy, more than a powerful electric heater.
The challenge of iSense is to reduce the size and the energy consumption of the apparatus to make it fit in a volume that could be manipulated and carried around by a single person, something like the size and weight of a large backpack. It should also be autonomous.