Sensitivity of Various Qubit Detection Methods in Pr:Y2SiO5

Abstract: The long coherence times of the 4f hyperfine levels of rare-earth-ions gives the possibility to use these as quantum computation devices. Moreover after being doped into a crystal the strong dipole-dipole interaction can be utilized to entangle them. Much work has been done here in Lund to attain as many of the DiVincenzo criteria as possible. At the moment work is being done in the creation of a multiple qubit gate, namely the controlled NOT gate. However, due to an exponential decay in the probability of attaining this gate with respect to the number of involved qubits, along with the low doping concentration, the number of atoms that take part in these gates will be very small. Detecting the signal from such a small population is problematic. This thesis addresses this problem by comparing the established readout method that consists of a simple scan, with two new readout methods: a slow scan, i.e., a scan with low frequency chirp and a method called superposition beating which incorporates the fundamentals of heterodyne detection with the free induction decay of an ensemble of atoms. A way of calculating the signal to background ratio in order to maximize the existing signal is also proposed and investigated. The results are then compared to Bloch simulations to give a more intuitive grasp of the quantities that are being discussed. Using the superposition beating method $7$\% of the maximum qubit population could be detected. Furthermore a population resolution of $2$ percentage points was achieved.