an atom with nuclear spin $I=9/2$, such as $^{87}$Sr.[]{data-label="fig:levelstructure"}](levelstructure){width="8.5cm"}

The key new feature of alkaline earth atoms in comparison with alkali atoms is the singlet-triplet metastable transition, with the $^1$S$_0$ – $^3$P$_0$ transition being used as the clock transition (see Fig. \[fig:levelstructure\]a). In particular, for $^{87}$Sr, the $^3$P$_0$ manifold has a measured lifetime of $\tau \sim 30$s, and the $^3$P$_2$ levels have even longer predicted lifetimes. In addition, for species with non-zero nuclear spin, this spin can be decoupled from the electronic state on the clock transition [@hayes07; @reichenbach07; @yi08; @aeshort; @Gorshkov2009], especially in the presence of a large magnetic field. The use of this nuclear spin for storage of quantum information would then be ideal, as the nuclear spin is much less sensitive to magnetic fields than electron spins, and thus much less susceptible to decoherence from magnetic field fluctuations than qubits stored on electronic states. This has lead to a series of proposals [@aeshort; @Gorshkov2009; @Shibata] in which the electronic state is used for access to and manipulation of the qubit [@dereviankoaddressing], and the nuclear spin state is used for qubit storage.

In previous work [@aeshort] we developed a scheme for quantum computing with alkaline earth atoms that 