The new work, by Andrew Daley and colleagues of the University of Innsbruck/ Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, JILA and Caltech, demonstrates that in certain situations experiments with alkaline earth atoms and similar species are better than quantum computing set-ups with neutral alkali atoms. "We show how completely independent lattices for two different internal states of the atoms can be created," Daley told nanotechweb.org. "These states can be used in a complete scheme for quantum computing and potentially other applications."
Two states
An important difference between atoms with two valence electrons and neutral alkali atoms (which have just one valence electron) is that they have a long-lived metastable excited state that is coupled to the electronic ground state via an optical transition. Daley and co-workers have exploited the fact that that atoms in the metastable state couple very differently to applied laser light than those in the ground state.
Thus, by using two different wavelengths of light, the researchers can create optical lattices (periodically repeating traps for atoms made using standing wave of laser light) that trap either the ground state or the metastable state, but not both. This means that you can have completely independent traps for the two states, explains Daley. "For example, we can place some atoms in the metastable state and some in the ground state and move them with respect to each other in a controlled fashion."
These unique properties can be exploited to entangle atoms and perform quantum information processing. For instance, the researchers can store atoms in the ground state in the optical lattice, with the qubit stored on the nuclear spin state, so that two different states of nuclear spin represent a 0 and 1 for quantum computing. Using the state of nucleus rather than the electronic state also means that the qubit is much less sensitive to its environment and so will have a longer coherence time. Long coherence times are crucial if qubits are to be used in real-world computing applications.
Daley and co-workers reckon that such a system should not be difficult to make in reality because it is similar to current state-of-the-art devices, such as those that use strontium atoms in optical clock experiments.
The work was published in Physical Review Letters.