Fifth-order nonlinear optical response of excitonic states in an InAs quantum dot ensemble measured with two-dimensional spectroscopy

Abstract

Exciton, trion and biexciton dephasing rates are measured within the inhomogeneous distribution of an InAs quantum dot (QD) ensemble using two-dimensional Fourier-transform spectroscopy. The dephasing rate of each excitonic state is similar for all QDs in the ensemble and the rates are independent of excitation density. An additional spectral feature -too weak to be observed in the time-integrated four-wave mixing signal -appears at high excitation density and is attributed to the χ (5) biexcitonic nonlinear response. The optical spectrum of semiconductor quantum dots (QDs) at low temperature is dominated by excitonic features including neutral and charged excitons (trions) and bound or anti-bound two-excitons (biexcitons)1 . Exciton dephasing times up to nanoseconds 2,3 have made semiconductor QDs attractive for applications in quantum information and coherent control, motivating studies investigating dephasing and relaxation mechanisms that can limit the performance of QD-based devices. The most widely-used technique for studying these properties has been spectrally-and time-resolve photoluminescence (PL) spectroscopies 4-6 , in which single QDs must be isolated to overcome significant inhomogeneous line broadening resulting from QD size dispersion. These experiments have demonstrated the effects of thermal broadening 7-11 on the exciton homogeneous lineshape and width (inversely proportional to the dephasing time) and on the multi-particle emission energies 12,13 . Additional insight into dephasing mechanisms and coherent interactions between excitons can be gained by using nonlinear techniques, in which many-body interactions give rise to distinct features in the nonlinear signals 14 . Transient four-wave mixing (FWM) has been particularly suitable for revealing the effects of phonon and inter-exciton scattering on the dephasing rate of excitons, biexcitons and trions even in the presence of strong inhomogeneity 15-18 . More recently, optical two-dimensional Fouriertransform spectroscopy 19 (2DFTS) -an extension of three-pulse FWM -has been demonstrated as an extremely sensitive tool for investigating coherent excitonic interactions 20-22 and incoherent relaxation dynamics 23 in interfacial GaAs QDs. 2DFTS is advantageous for investigating QD ensembles because of its ability to unfold the coherent response onto two frequency dimensions, separating the homogeneous and inhomogeneous linewidths and clearly isolating different spectral features that would otherwise overlap using one-dimensional techniques. In this Brief Report, we use 2DFTS to investigate the nonlinear optical response of excitons, trions and biexcitons in an InAs QD ensemble by exploiting the dipole transition selection rules for this system. 2DFTS has not been applied previously to the study of InAs QDs, which exhibit stronger confinement compared to GaAs QDs, and therefore smaller dipole moments, making them more difficult to study. By using co-and cross-linearly polarized excitation and detection schemes, we isolate the different excitonic s...

Homogeneous linewidth narrowing of the charged exciton via nuclear spin screening in an InAs/GaAs quantum dot ensemble

“…However, singledot experiments, which require long signal integration times, still suffer from spectral diffusion effects that mask the intrinsic recombination dynamics [4,13,14]. These limitations can be avoided by investigating QD ensembles using spin noise spectroscopy [15,16] or nonlinear optical spectroscopy techniques, such as spectral hole burning [17][18][19], four-wave mixing [20], or coherent multidimensional spectroscopy [21,22]. An ultralong coherence time up to ∼1.5 ns, corresponding to a sub-μeV dephasing rate, has been measured for the positively charged exciton in InAs QDs at cryogenic temperature [23].…”

Dynamics of excitons in individual InAs quantum dots revealed in four-wave mixing spectroscopy

“…For the experimental investigations we implement a heterodyne spectral interferometry technique [15] to retrieve polarization-resolved four-wave mixing (FWM) signals. While FWM has often been used to infer exciton dynamics in QWs [16] or for QD ensembles [17], for single QDs the experiments are more challenging because of the weak signal intensity. This longstanding issue has recently been solved by exploiting photonic nanostructures to enhance non-linear responses.…”

Multidimensional coherent optical spectroscopy of semiconductor nanostructures: a review

“…A particularly successful example is the Multidimensional Optical Nonlinear Spectrometer (MONSTR) experiment [34,46], combining active feedback with an ultrastable platform. The MONSTR has been able to capture coherence time and measure homogeneous linewidths of semiconductor QWs [7,47] and QD ensembles [48,49]. In this kind of experiment where mechanical delay lines are used, liquid crystal retarders can be added to implement phase-cycling algorithms as a way to further isolate the FWM signal from other contributions [34].…”

“…A power dependence to check that the signal intensity scales with P 3 (with P the average power in the excitation beams) is needed to ensure that the observed signal is dominated by third-order contributions -and can be used to separate higher-order contributions within a two-dimensional spectrum [49].…”