Laboratoire de Physique Théorique
Toulouse - UMR 5152

Decoherence is the main concern in experimental realizations of quantum computers. In order to control the quantum computer, a certain amount of interaction with its environment is needed that destroys in general the phase coherence of the computer very quickly. An article in NJP, which was now selected as one of the 10th Anniversary Highlights articles by the editors of the journal, explains how this dilemma can in principle be avoided.

In general, the stronger the coupling to the environment, the faster the decoherence. However, the article explains that in the presence of a Decoherence Free Subspace (DFS) a relatively strong coupling to the environment is advantageous. DFS may arise if the coupling to the environment has a certain symmetry, such that the environment, considered as a measurement apparatus, cannot distinguish between the states of the quantum computer. A strong coupling to the environment will confine the dynamics of the quantum computer effectively to the DFS, and thus prevent decoherence. The article, which is freely accessible in the online Journal New Journal of Physics, showed explicitly how to construct one of the fundamental two qubit gates necessary for quantum computation effectively in a DFS of a cavity-QED system. (Contact : D. Braun)