Excitonic Quantum Devices

Abstract

An exciton is a bound state of an electron and a hole exhibiting bosonic characteristics at low densities, making it a promising contender for Bose-Einstein Condensation (BEC) [1] in many-body systems. The formation of excitonic BEC depends on a characteristic exciton density and can occur at significantly higher temperatures ranging from a few Kelvins to room temperature due to a much smaller mass of excitons compared to atoms like rubidium. Building upon prior research from our laboratory [2], we have explored 0D-2D hybrid structures, specifically quantum dots (QDs) integrated with 2D materials, as an ideal platform for studying excitonic BEC. Under reverse bias, the electrons occupy the triangular quantum well-formed near the AlAs potential barrier, and holes are in the InAs quantum dot, forming indirect excitons that provide a unique opportunity to investigate collective quantum phenomena. Our previous studies have demonstrated that the evolution of photo-capacitance spectra under varying bias serves as an indicator of Hadamard gate operations on a collective, two-level excitonic quantum state undergoing BEC. In this project, we extend these investigations to the time-domain photo-response of 0D-2D mixed-dimensional semiconductors. As excitons behave like tiny dipoles with varying voltage, they align and misalign, showing phase coherent oscillations. This happens because of resonant tunneling. Initially, we measured photo capacitance across different frequencies and bias conditions under illumination, identifying the optimal parameters for time-domain studies. Given our prior observation [2] of Rabi oscillations with varying light intensity, we further probed the sample using pulsed light at the selected conditions. The resulting photo response exhibited oscillatory behaviour in the time domain, which was repeatedly verified under different parameter variations. To further substantiate our findings, we examined these oscillations at elevated temperatures and they tend to die, showing the existence of some damping mechanism. We anticipate establishing these oscillations as Rabi oscillations and have also devised an experimental method to apply a sequence of pulses for quantum gate operations, which we aim to execute in future studies.