Physicists of the University of Bonn have taken one more important hurdle on the path to what is known as a quantum computer: by using ‘laser tweezers’ they have succeeded in sorting up to seven atoms and lining them up. In the experiment the research team headed by Dr. Arno Rauschenbeutel and Professor Dieter Meschede decelerated several caesium atoms for a period of several seconds so that they were hardly moving, then loaded them onto a ‘conveyor belt’ consisting of lasers. This conveyor belt is made up of a standing light wave composed of many peaks and troughs – possibly comparable to a piece of corrugated iron. ‘Unfortunately it cannot be predicted which trough precisely the atoms will land in,’ Arno Rauschenbeutel explains. ‘It’s rather like pouring several eggs from a big dish into an egg carton – which section each egg rolls into is a matter of chance.’
However, anyone wishing to calculate with atoms must be able to place them exactly. ‘All the atoms on the conveyor belt have to have the same distance from each other,’ is how Arno Rauschenbeutel sketches the challenge. ‘Only then can we get them to interact in a controlled way in what is called a quantum gate.’ By lining up gate operations like these it would already be possible to carry out simple quantum calculations.
The next aim of the Bonn physicists is to construct a quantum gate. For this purpose they want to ‘write’ quantum information onto two caesium atoms and then place them between two tiny mirrors. The intention is that they should interact there with each other, i.e. exchange information by emitting and absorbing fluorescent light. If this is successful, it will be the next milestone for the Bonn researchers on their way to the quantum computer.