Alexander Högele


Ludwig-Maximilians-Universität München

Faculty of Physics

Geschwister-Scholl-Platz 1

80539 Munich

Tel. +49 89 2180 1457


Group Webpage


Research Webpage: quantum nano-systems, quantum dots, quantum optics

We study quantum phenomena in optically active low-dimensional condensed matter systems. Conceptually similar to optical spectroscopy of atoms or ions, we use light-matter interaction as an interface between photon and quantum degrees of freedom in solid-state nanoscale systems. The main research lines include experimental quantum optics with quasi zero-dimensional emitters and one-dimensional carbon nanotubes, bottom-up assembly of photofunctional nanosystems by DNA-origami, and novel truly two-dimensional atomic layer semiconductors.

Quantum emitters such as semiconductor quantum dots, nitrogen-vacancy centers in nanodiamond or single-walled carbon nanotubes represent versatile model systems for solid-state quantum optics. Discrete spectra with non-classical photon emission statistics or high degree of spin polarization render individual quasi zero-dimensional systems ideal candidates for the implementation of experimental quantum science by all-optical means.

The interdisciplinary project explores the potential of DNA-assembly for the construction of complex photofunctional nanosystems. It merges recent achievements in biophysics and solid-state nanosciences for DNA-guided fabrication of functional units based on radiant dyes, quantum dots, nanodiamonds and metal nanoparticles. The goal of the project is to establish a tool-box for bottom-up nanometer-precise assembly of photonic systems. Our collaboration partners in the project are the groups of T. Liedl (LMU), A. O. Govorov (Ohio University, Athens, USA), and E. Lifshitz (Technion, Haifa, Israel).

Atomic-layer transition metal dichalcogenides such as MoS2 or WSe2 have emerged recently as novel truly two-dimensional material systems with remarkable optoelectronic properties. Single layer materials combine reduced screening and direct band gap optical transitions. While strong Coulomb interactions enhance phenomena of exciton binding and quantum confinement, strong spin-orbit coupling mediates robust valley coherence that can be mapped onto the photon polarization degrees of freedom. Our collaboration partner in the project is H. Yamaguchi, Los Alamos National Laboratory, Los Alamos, USA.


Photon Correlation Spectroscopy of Luminescent Quantum Defects in Carbon Nanotubes

M. Nutz, J. Zhang, M. Kim, H. Kwon, X. Wu, Y. Wang, A. Högele.

Nano Letters (2019).

Show Abstract

Defect-decorated single-wall carbon nanotubes have shown rapid growing potential for imaging, sensing, and the development of room-temperature single-photon sources. The key to the highly nonclassical emission statistics is the discrete energy spectrum of defect-localized excitons. However, variations in defect configurations give rise to distinct spectral bands that may compromise single-photon efficiency and purity in practical devices, and experimentally it has been challenging to study the exciton population distribution among the various defect-specific states. Here, we performed photon correlation spectroscopy on hexyl-decorated single-wall carbon nanotubes to unravel the dynamics and competition between neutral and charged exciton populations. With autocorrelation measurements at the single-tube level, we prove the nonclassical photon emission statistics of defect-specific exciton and trion photoluminescence and identify their mutual exclusiveness in photoemissive events with cross-correlation spectroscopy. Moreover, our study reveals the presence of a dark state with population-shelving time scales between 10 and 100 ns. These new insights will guide further development of chemically tailored carbon nanotube states for quantum photonics applications.

DOI: 10.1021/acs.nanolett.9b02553

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