Quantum Dot Qubits

I had seen these results in a previous talk, but now the paper is out in Nature Science. Charles Marcus’s group at Harvard has been working on building a qubit from a semiconductor quantum dot. One of the difficulties for this type of qubit is that the qubit couples via a hyperfine interaction to surrounding nuclei. If you don’t do anything about this hyperfine interaction, this causes a typical Rabi flopping experiment to exhibit decoherence rates of 10 nanoseconds. Way to short to make a useful quantum computer! But what is nice about the hyperfine decoherence mechanism, is that it is a constant coupling which can be overcome by doing a spin echo experiment. In the above paper, Marcus and colleagues show that with appropriate spin echo techniques, they get lifetimes of 1 microseconds. Nothing like that many orders of magnitude improvement, no?