Speaker: Kai Müller, Walter Schottky Institut, TUM School of CIT, and MCQST Technical University of Munich

Title: Dynamics of non-classical light generation from quantum dots

Abstract: Sources of non-classical light, such as single photons and entangled photons, are of paramount importance for future applications in photonic quantum technologies. Due to their excellent optical properties, such as fast emission rates and nearly transform-limited linewidth, semiconductor quantum dots are promising as on-demand sources in such applications, but also for testing fundamental quantum-optical predictions. 

In recent years, many excitation schemes have been developed to optimize the source performance, each with their specific advantages and disadvantages. In this seminar, I will review and benchmark the most prominent schemes. 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. 

The stimulated excitation scheme [4] is based on the resonant two-photon excitation of the biexciton followed by a precisely timed stimulation of the biexciton-exciton transition, which effectively prepares the system in an exciton state. On the one hand, the two-photon excitation of the biexciton suppresses re-excitation and enables ultra-low multi-photon errors. On the other hand, the precisely timed stimulation pulse prepares the system in the exciton state at a well-defined time. This strongly reduces timing jitter in the preparation of the exciton state caused by the biexciton population lifetime and consequently enables simultaneously high purity and indistinguishability. 

The swing-up excitation technique uses the interplay of two red-detuned pulses for efficient state preparation [5]. In a recent study, we analyzed this method over a wide parameter range and explored its coherence properties [6]. Specifically, as a function of individual detuning and excitation power of the two pulses we find several resonances, confirming the coherent nature of the light-matter interaction. Moreover, we analyze the impact of the excitation technique on the single-photon properties of the generated photons.
 

References:
[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] T.K. Bracht, PRX Quantum, 2, 040354 (2021).
[6] K. Boos et al., Advanced Quantum Technologies, 2300359 (2024)

Bio: Kai Müller is Associate Professor at the Technical University of Munich (TUM), Germany, where he leads the Quantum Electronics and Computer Engineering group (QEC). His research focusses on the development of building blocks for photonic quantum technologies, such as non-classical light sources, spin-photon interfaces or single-photon detectors, as well as their integration into quantum photonic integrated circuits. After completing a Ph.D. in physics at TUM, he worked as a postdoctoral researcher at Stanford University. Subsequently, he established a junior research group at the Walter Schottky Institute of TUM. In 2019, he was appointed as assistant professor at TUM and obtained early tenure as associate professor in 2022.