Single-ion readout

Nature 497, 91–95 (2013)

Measuring the electron spins associated with single defects in solids is a critical task in the field of quantum information processing. However, it is difficult to achieve the required high fidelities with the two material systems usually employed — phosphorus dopants in silicon and nitrogen–vacancy centres in diamond. Now, Chunming Yin and co-workers from the University of New South Wales, the University of Melbourne and the Australian National University in Australia have demonstrated a hybrid optical–electrical readout technique to overcome these drawbacks. The researchers used a single-electron transistor, which works as a charge sensor, to investigate the charge state of single erbium ions (Er³⁺) implanted in silicon. First, they cooled the Er-implanted single-electron transistor to 4.2 K. They then tuned the wavelength of the excited beam to the resonant wavelength of the ⁴I_I5/2–⁴I_I3/2 transition of Er³⁺, which allowed the charge displacement induced by an ionization event to change the tunnelling current of the single-electron transistor. This permitted real-time observation of the charge state of an Er defect centre in silicon, thus avoiding the bottleneck of photon collection. When the researchers applied a magnetic field to the single-electron transistor, they observed eight resonant peaks, with a photon energy difference of around 0.2 μeV. This approach avoids the thermal broadening limitation of an all-electrical readout scheme and has potential for the single-shot readout and manipulation of nuclear spin states.