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.

Tailored nanoscale quantum light sources, matching the specific needs of use cases, are crucial building blocks for photonic quantum technologies. Several different approaches to realize solid-state quantum emitters with high performance have been pursued and different concepts for energy tuning have been established. However, the properties of the emitted photons are always defined by the individual quantum emitter and can therefore not be controlled with full flexibility. Here we introduce an all-optical nonlinear method to tailor and control the single photon emission. We demonstrate a laser-controlled down-conversion process from an excited state of a semiconductor quantum three-level system. Based on this concept, we realize energy tuning and polarization control of the single photon emission with a control-laser field. Our results mark an important step towards tailored single photon emission from a photonic quantum system based on quantum optical principles.

In our work, we have engineered low capacitance single quantum dot photodiodes as sensor devices for the optoelectronic sampling of ultrafast electric signals. By the Stark effect, a time-dependent electric signal is converted into a time-dependent shift of the transition energy. This shift is measured accurately by resonant ps laser spectroscopy with photocurrent detection. In our experiments, we sample the laser synchronous output pulse of an ultrafast CMOS circuit with high resolution. With our quantum dot sensor device, we were able to sample transients below 20 ps with a voltage resolution in the mV-range.The field of quantum sensing has attracted tremendous interest during the last decades. The use of quantum systems as sensors promises high sensitivity, high precision, and access to nanoscale applications [1]. Today, quantum sensors detect a wide range of physical quantities such as magnetic fields, electric fields, temperature, and even gravity. With our present work we contribute to the field of electric field sensing. Here, existing concepts for quantum sensing rely mainly on diamond NVcenters with a special focus on the nanoscale [2], and on Rydberg atoms for RF-field sensing [3].In this contribution, we use single semiconductor quantum dots (QDs) and ps laser techniques to demonstrate QD-based electric field sensing with ultrafast time-resolution. At low temperatures, QD exciton ground state transitions have extremely narrow line width [4] and excellent coherence properties, allowing for coherent state control [5,6]. Integrated in diode structures, their transition energies are electric field tunable with high precision via the Stark effect. For resonant excitation, single QD photodiodes act as voltage tunable spectrometers, which also allow for electric read-out by photocurrent detection [7,8]. We have engineered radio frequency (RF) compatible single QD Schottky-photodiodes as sensor devices for the sampling of ultrafast electric signals applied to the Schottky-gate. The optoelectronic sampling concept relies on resonant ps laser excitation and tracing of the QD exciton resonance via a back-gate voltage for each time step. For the demonstration of optoelectronic sampling we used the laser synchronous output pulse of an ultrafast CMOS circuit, which was connected to the Schottky-gate of the QD photodiode.