Researchers engineer molecular magnets to act as long-lived qubits

[Bill USA]

http://www.physorg.com/news/2012-03-molecular-magnets-long-lived-qubits.html

Now a team of researchers from the UK have demonstrated that the phase of quantum mechanical superpositions between the magnetic states can last for more than 15 microseconds, allowing their spin states to be repeatedly switched before they lose their information through decoherence. This finding adds to the evidence that molecular magnets may be useful as qubits, the components of a quantum computer.

The researchers, C.J. Wedge, et al., from the University of Oxford and the University of Manchester, have published their study on how to chemically engineer molecular qubits to increase their phase memory times in a recent issue of Physical Review Letters. Previously, the researchers achieved a phase memory time of 3.8 microseconds, and studies of other molecular magnet systems have yielded times on the 1 microsecond time scale.

“Phase memory time and coherence time are very similar concepts,” coauthor Arzhang Ardavan of the University of Oxford told PhysOrg.com. “[Long phase memory time] means that it is possible to manipulate the qubit many times before the quantum information is lost. That is the greatest significance, but we were also pleased that it was possible to control the molecular structures precisely so as to determine the various decoherence mechanisms and to reduce them as far as we were able.”

In their study, the researchers focused on Cr7Ni molecular magnets, which they had previously shown to have coherence times that greatly exceed the 10 nanoseconds needed for single-qubit manipulations. Here, they have taken the next steps and investigated the specific sources of the molecular magnet's decoherence (nuclear spin diffusion and spectral diffusion), as well as how to optimize the structures to delay decoherence as long as possible.
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