PHYSICAL REVIEW X
We have shown that a highly efficient QD-cavity interface makes it possible to monitor in real time single quantum events at the microsecond time scale. This is illustrated here by monitoring in real time single-charge jumps, evidencing a measurement rate 5 orders of magnitudefaster than for previous optics experiments of directsingle-charge sensing. Our technique relies oncoherent reflection spectroscopy, performed with a detectionsetup approaching the shot-noise limit, on a deterministically coupled QD-pillar cavity device, into whichthe incident photons are injected with a high input-coupling efficiency.
This ensures that almost every incident photon interacts with the QD and provides an opticalresponse highly sensitive to the QD transition energy. Single events, corresponding to the capture and release of a single charge by a material defect, are distinctlyidentified with a few microseconds time resolution and with a less than 0.2% error probability. Our measurementsalso reveal a photoinduced acceleration of the chargedynamics.
Figure: (a),(b) Band structures of an InGaAs QD with a nearby loaded or empty trap (c),(d) Typical reflectivity spectra for a loaded and for an empty trap. (e) Scatter plot of measured reflectivity values versus photon energy. (f) Real-time reflectivity signal. Dashed horizontal lines are guides to the eye indicating the two states with reflectivities RL and RE. (g) Histogram of the reflectivity values