Condensed Matter Seminar: Spectral diffusion and the Stark effect in colloidal quantum dots

While colloidal quantum dots (CQDs) have become an important building block in electro-optical devices, in the realm of quantum science and technology, they are often considered inferior to other types of quantum emitters such as solid-state defects and epitaxial quantum dots. Despite their single-photon emission [1], demonstrations of quantum coherence and control are largely still lacking. The main obstacle towards these is spectral diffusion – stochastic fluctuations in the energy of photons emitted from an individual CQD even at cryogenic temperatures. In this talk, I will present our recent work providing, for the first time, direct and definitive proof that these fluctuations arise from stochastic electric fields in the micro environment [2]. The high sensitivity of CQDs to electric fields, through the quantum-confined Stark effect, is not only a bug but also a feature - broadband coherent control of the temporal wavefunction of the emitted photon. To fulfill the unique potential that CQDs hold in the field of quantum optics, spectroscopy at fast-to-ultrafast (milliseoncd-to-femtosecond) timescales, relying on tools from terahertz and femtosecond-laser toolboxes [3,4], will play a detrimental role.

[1]    R. Tenne, U. Rossman, B. Rephael, Y. Israel, A. Krupinski-Ptaszek, R. Lapkiewicz, Y. Silberberg, and D. Oron, Super-Resolution Enhancement by Quantum Image Scanning Microscopy, Nature Photonics 13, 116 (2019).

[2]    F. Conradt, V. Bezold, V. Wiechert, S. Huber, S. Mecking, A. Leitenstorfer, and R. Tenne, Electric-Field Fluctuations as the Cause of Spectral Instabilities in Colloidal Quantum Dots, Nano Lett. 23, 9753 (2023).

[3]    P. Henzler et al., Femtosecond Transfer and Manipulation of Persistent Hot-Trion Coherence in a Single CdSe/ZnSe Quantum Dot, Physical Review Letters 126, 067402 (2021).

[4]    P. Fischer, G. Fitzky, D. Bossini, A. Leitenstorfer, and R. Tenne, Quantitative Analysis of Free-Electron Dynamics in InSb by Terahertz Shockwave Spectroscopy, Physical Review B 106, 205201 (2022).