Optoelectronic sampling of ultrafast electric transients with single quantum dots

Abstract

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.