We demonstrate electrically controlled robust state preparation of an exciton qubit by rapid adiabatic passage with Fourier-limited laser pulses. In our approach, resonant ps laser pulses are applied to generate excitonic population in a quantum dot, whereas synchronously applied ps electric transients provide a controlled sweep of the exciton transition energy. The ps electric transients applied to the quantum dot in a diode structure result in ultrafast Stark shifts of the exciton energy on time scales below the decoherence time of the exciton. We experimentally demonstrate that the tailored electric chirp of the exciton energy leads to a controlled rapid adiabatic passage, which results in a robust state preparation of the exciton. Our experimental results are confirmed by a theoretical analysis of the chirped coherent manipulation of the exciton two level system. Our approach toward optoelectronic quantum control paves the way for broader applications that require a scalable control of functional coherent systems.

We report on the coherent phase manipulation of quantum dot excitons by electric means. For our experiments, we use a low capacitance single quantum dot photodiode which is electrically controlled by a custom designed SiGe:C BiCMOS chip. The phase manipulation is performed and quantified in a Ramsey experiment, where ultrafast transient detuning of the exciton energy is performed synchronous to double pulse π/2 ps laser excitation. We are able to demonstrate electrically controlled phase manipulations with magnitudes up to 3π within 100 ps which is below the dephasing time of the quantum dot exciton.

We report static and dynamic photocurrent response from sub-stoichiometric a-SiNx:H thin films. The photocurrent spectral (PCS) response is peaked in the technologically important optical energy range of 2.2 to 4.5 eV. The transient photocurrent response with prolonged exposure is attributed to reduction in number of charge carriers due to trapping of photo-generated carriers at defect sites. The narrow PCS response is attributed to dominant photo-generation of carriers in the bandtails of stoichiometric Si3N4 phase and subsequent transport through the excess Si network.

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