Humboldt-Universität zu Berlin - Faculty of Mathematics and Natural Sciences - Department of Physics

Department Colloquium: Prof. Dr. Kai Müller (Technical University of Munich) talks about this topic:

Quantum Science with Tweezer Arrays

Abstract

Photonic quantum technologies rely on the ability to generate, process, and detect quantum states of light. Realizing the best possible building blocks for theses task requires to develop a deep understanding of the underlying physical processes. This talk will provide insights into 
 the generation of quantum light from optically active few-level quantum systems, represented here by semiconductor quantum dots [1-5]. Moreover, our recent progress in pushing the limits of superconducting nanowire single photon detectors (SNSPDs) via local He-ion irradiation will be discussed [6-8].

For the generation of single photons from quantum dots, many excitation schemes have been developed in recent years to optimize the source performance, each with their specific advantages and disadvantages. Resonant excitation allows for the generation of highly indistinguishable photons, while the single-photon purity is limited by reexcitation [1]. In contrast, two-photon excitation of the biexciton suppresses reexcitation, resulting in ultra-low multi-photon errors [2]. However, the indistinguishability of emitted photons is inherently limited by the cascaded decay [3]. In order to avoid such limitations, advanced excitation schemes that involve multiple pulses or pulses with multiple frequency components were developed [4-5].

SNSPDs are promising for photonic quantum technologies, as they simultaneously offer high detection efficiencies, low dark count rates, low timing jitter, and high count rates. Interestingly, their sensitivity can be enhanced via Helium-ion irradiation [6]. This can be used to mitigate the effect of current crowding for arbitrary detector geometries [7]. Finally, the origin of the performance improvement will be discussed [8]

[1] K. A. Fischer, et al., Nature Physics 13, 649-654 (2017)
[2] L. Hanschke et al., npj Quantum Information 4, 43 (2018)
[3] E. Schöll et al., Physical Review Letters 125, 233605 (2020)  
[4] F. Sbresny et al., Physical Review Letters 128, 093603 (2022)
[5] K. Boos et al., Advanced Quantum Technologies, 2300359 (2024)  
[6] S. Strohauer et al., Advanced Quantum Technologies 6, 2300139 (2023)
[7] S. Strohauer et al., Science Advances 11, eadt0502 (2025)
[8] S. Strohauer et al., APL Quantum 2, 026131 (2025)

The Colloquium will be held in "hybrid" format, i.e., you can join the talk in the lecture hall or via zoom.

Zoom Link:
https://hu-berlin.zoom.us/j/64567336962?pwd=QjhyMW5SbFVBZWVNRWJrTFBFN2Rtdz09
Meeting-ID: 645 6733 6962
Passwort: 607723