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We report on scalable heterointegration of superconducting electrodes and epitaxial semiconductor quantum dots (QDs) on strong piezoelectric and optically nonlinear lithium niobate. The implemented processes combine the sputter-deposited thin film superconductor niobium nitride and III–V compound semiconductor membranes onto the host substrate. The superconducting thin film is employed as a zero-resistivity electrode material for a surface acoustic wave resonator with internal quality factors Q ≈ 17 000 representing a three-fold enhancement compared to identical devices with normal conducting electrodes. Superconducting operation of ≈ 400 M H z resonators is achieved to temperatures T > 7 K and electrical radio frequency powers P r f > + 9 d B m . Heterogeneously integrated single QDs couple to the resonant phononic field of the surface acoustic wave resonator operated in the superconducting regime. Position and frequency selective coupling mediated by deformation potential coupling is validated using time-integrated and time-resolved optical spectroscopy. Furthermore, acoustoelectric charge state control is achieved in a modified device geometry harnessing large piezoelectric fields inside the resonator. The hybrid QD—surface acoustic wave resonator can be scaled to higher operation frequencies and smaller mode volumes for quantum phase modulation and transduction between photons and phonons via the QD. Finally, the employed materials allow for the realization of other types of optoelectronic devices, including superconducting single photon detectors and integrated photonic and phononic circuits. [ABSTRACT FROM AUTHOR]

We review our recent work on multi-dimensional coherent optical spectroscopy (MDCS) of semiconductor nanostructures. Two approaches, appropriate for the study of semiconductor materials, are presented and compared. A first method is based on a non-collinear geometry, where the Four-Wave-Mixing (FWM) signal is detected in the form of a radiated optical field. This approach works for samples with translational symmetry, such as Quantum Wells (QWs) or large and dense ensembles of Quantum Dots (QDs). A second method detects the FWM in the form of a photocurrent in a collinear geometry. This second approach extends the horizon of MDCS to sub-diffraction nanostructures, such as single QDs, nanowires, or nanotubes, and small ensembles thereof. Examples of experimental results obtained on semiconductor QW structures are given for each method. In particular, it is shown how MDCS can assess coupling between excitons confined in separated QWs. [ABSTRACT FROM AUTHOR]

The effects of confinement on biexciton renormalization in self-assembled InAs and interfacial GaAs quantum dot (QD) ensembles are studied using two-dimensional Fourier-transform spectroscopy. We find that in thermally annealed InAs QDs, changes in the biexciton transition energy are strongly correlated with those of the exciton and that the biexciton binding energy is similar for all QDs in the ensemble. These results are in contrast to those from GaAs QDs formed from interfacial fluctuations of a narrow quantum well (QW). In both the GaAs QW and QDs, correlation is reduced and the biexciton binding exhibits a strong dependence on localization. Comparison with simulations reveals how confinement and Coulomb interactions modify biexciton renormalization. [ABSTRACT FROM AUTHOR]