We recently built a pulsed electron spin resonance (ESR) system operating at 2.5 GHz that enables complex pulse shaping for quantum engineering purposes. This system is being used to explore Hamiltonian Engineering of dipolar-coupled P1 centers in diamond.
NMR has very low detection sensitivity and we need on the order of a billion nuclear spins (protons) to detect a signal inductively even at liquid helium temperatures. For inductive detection of electron spins, we can reduce this to about a million spins. It is possible to go much lower if we use alternative detection strategies such as optical or electrical detection, though these are known to only work in a limited number of samples. Techniques such as magnetic-resonance force microscopy aim to improve the detection sensitivity of NMR and ESR to the single spin level for arbitrary samples.
Phosphorus-doped silicon is a particularly interesting solid-state spin system due to its long coherence time and the potential for making complex devices using advanced fabrication technology. Electrical readout of electron and hence, nuclear spins in Si:P at low magnetic fields is mediated by spin-dependent carrier recombination. Since an interaction with surface states is necessary for modifying bulk carrier density for observation under spin-resonant conditions, electrically detected magnetic resonance (EDMR) in Si:P is inherently sensitive to only those donors located within roughly the first 20nm of surface.
The low-field EDMR setup in our lab can operate at both continuous wave and pulse mode. For cwEDMR, frequency modulation is implemented instead of field modulation. Although magnetic field modulation through Helmholtz coils has traditionally been used for lock-in detection of cwESR and cwEDMR, mechanical vibration due to the Lorentz forces puts limitation on the detection sensitivity. In order to further enhance signal intensity for cwEDMR, we also investigate the effect of different optical excitation to Si:P sample at liquid helium temperature. We have different light source and a continuously variable laser from 1049nm to 1090nm.