Question: How can etremely cold atoms used to supercomputers? Can you please share about your research on this?

Chris Mansell answered on 23 Jun 2013:

Hi usman100,

In the lab, we have a box with no air in it. It’s called a vacuum chamber. We put some rubidium atoms in there. We cool these atoms using laser beams. We do this because they would be moving too fast for us to study if they were at room temperature (i.e. at a few hundred metres per second). They get cooled to a few millionths of a degree above absolute zero (which is colder than outer space). This reduction in temperature equates to them travelling at a few centimetres per second. We also trap these atoms in one place. We do this by applying a magnetic field. We can then take away the magnetic field and change the laser beams from the ‘cooling configuration’ to the ‘trapping configuration.’

To get these cold atoms to do a computation, we need to be able to control them very well. We can do this by using lasers to manipulate the electrons of the atoms. Just like with ordinary computers, we can say that a given situation represents a zero and a different situation represents a one. In ordinary computers, an uncharged capacitor represents a zero and a charged capacitor represents a one. With our cold atoms, one electronic state represents a zero and another electronic state represents a one.

You may have read or heard that objects that are best described by quantum mechanics can be in two places at once. More generally, such an object (e.g. an atom) can be in two states at once. This means that we can have our atoms representing zeros and ones at the same time. This is like an amazing form of parallel processing.

The power of the ‘quantum computers’ comes from the following. 1 atom can be in 2 states at the same time. 2 atoms can be in 4 states at the same time. 3 atoms can be in 8 states at the same time. Generally, n atoms can be in 2 to the power of n states at the same time. Recall that ordinary computers can only be in one configuration at a time. Even when n is quite small (i.e. we don’t have that many atoms) we still have an absolutely massive number of states (that represent the zero and one values of a computation) all at once. Try typing 2 to the power of 100 into your calculator and you will see what I mean. (I use this example because I intend to experiment on about 100 atoms.)

To process the information, we need to do conditional “if … then …” logic. That is, we need to get the state of one atom to depend on the state of other atoms. We can get them to interact with each other so that this can happen.

At the end of the computation, we need to find out the answer. We do this by seeing what light the atoms emit. To do this, we need a very good optical set-up and a sensitive camera. (I designed the optical set-up for my lab in the first year of my PhD.)

I hope this has helped.

Best wishes,
Chris