Question: How do you control or remove 'Quantum Decoherence' while doing your experiment?

Chris Mansell answered on 17 Jun 2013:

I would say there are three ways: closed-loop control, open-loop control and in-built protection.

In closed-loop control, you spot errors and then correct them. One way to do this is to have, say, three atoms that are supposed to be in the same quantum state. If one of them has had their state changed so that it is different from the two others, there are ways to check whether this has happened and put it back to the state it should be in.

In open-loop control, you apply laser-pulses to your atoms that decouple it from sources of noise.

There is more than one way of obtaining some in-built protection. There are certain quantum states that undergo less decoherence than others (because they don’t interact with the sources of noise much less). A set of such states is known as a decoherence-free subspace. You could try to do your computation with only those states. A much better, but also harder, way of getting some in-built protection involves something called topological quantum computing. Basically, the topological properties of a quantum system don’t get disturbed very easily by ordinary decohering processes. Physicists are still in the early stages of experimenting with the topological properties of quantum systems so it’s not as easy as some of the other techniques mentioned above.