Illustration: Alan Stonebraker

Figure 1: Protocol for improving the readout signal from a single nitrogen-vacancy ($NV-$) center in diamond: $NV-$ centers arise when a substitutional nitrogen atom ($N$) is next to a vacancy ($V$) as shown in the inset. The traditional readout technique used by most researchers to date is shown schematically as Route $1$, which connects the two states that form the logical qubit without involving the nuclear spin state of the $14N$. However, by driving the system along route $2$ and then $3$, the signal-to-noise is increased by $3$. This technique is universal because it works for an $NV-$ center in any local environment. The states are labeled by $|$electron spin state, $14N$ nuclear spin state$〉$. Routes $1$ and $3$ proceed via the excited states, and route $3$ requires a level anticrossing (LAC) in the excited states, reached by the application of a $50mT$ magnetic field.