HOW do you trap an atom? Make it look at itself in a mirror. That鈥檚 the odd conclusion from physicists who used an atom鈥檚 mirror image to freeze it in place. But the result is not just a curiosity 鈥� the mechanism gives physicists perhaps their best means yet of controlling the motion of trapped atoms.
Physicists have been using light to hold atoms in place since the 1970s. For instance, so-called optical tweezers work by using lasers to create an interference pattern of light and dark fringes. Atoms can be trapped in the 鈥渨ells鈥� of low energy, much like eggs in the hollows of an egg box. Trapped atoms are used in atomic clocks and could also be essential for building quantum computers.
Now a team at the Institute for Experimental Physics in Innsbruck, Austria, has shown how an atom can be trapped within its own interference pattern. First they illuminate a single barium atom with a laser, causing the atom to fluoresce. 鈥淲e position the [fluorescing] atom about 25 centimetres in front of the mirror and then align it so that we no longer see its reflection,鈥� says team member J眉rgen Eschner, who is now at the Institute of Photonic Sciences in Barcelona, Spain. When the atom is accurately positioned, its emitted and reflected light create an interference pattern that holds the atom in place.
Advertisement
Christoph Becher, another member of the Innsbruck team, says the mirror technique can be used to limit the jiggling of atoms held in traditional traps such as optical tweezers. As the atom moves off centre, it scatters more light from the brighter region of the mirror-induced interference pattern and less light from the darker fringes. The intensity of this scattered light therefore provides a simple measure of the atom鈥檚 movement, and can be fed back to fine-tune, say, the optical tweezers鈥� grip.
鈥淚t鈥檚 a nice bit of physics,鈥� says Andrew Steane, an atom and ion-trap specialist at the University of Oxford.