Coherent Spectroscopy of Multiple Excitons in Colloidal Nanocrystal Quantum Dots

Abstract Over three decades of intense research on colloidal semiconductor nanocrystal quantum dots (QDs) have passed, and the multitude of physical effects in QD systems still makes fascinating discoveries even today. In particular, the use of multiple excitons and their coherence is a hot topic to be investigated. We explore the potential of colloidal QDs for next‐generation optoelectronic applications. Here, we summarize our recent studies on the multiple‐exciton harmonic quantum coherence in PbS QDs. The multiple excitonic coherence can be observed with our newly developed system for phase‐locked interference detection of transient absorption signals. We found that multiple excitons exhibit dipole oscillations with integer multiples of the exciton resonance frequency. An important practical feature of this harmonic quantum coherence of multiple excitons is that it assists photoabsorption processes. Therefore, harmonic quantum coherence is a key to realize advanced optoelectronic applications.