| SS 2020
SS 2020

Fachbereichskolloquien

Allgemeines Physikalisches Kolloquium

07.05.2020

Development and physics of quantum dot devices for applications in photonic quantum technology

Prof. Dr. Stefan Reitzenstein
TU Berlin / Institut für Festköperphysik

Zeit: Donnerstag, 16 Uhr c.t.

Zugangsdaten:
https://wwu.zoom.us/j/93012126842
Meeting-ID: 930 1212 6842
Passwort: WWU_2020

Photonic quantum devices are key building blocks for the implementation of quantum communication protocols and for the realization of photonic quantum processors. Moreover, they allow one to explore exciting physics in the quantum regime of single emitters and single photons. Of particular interest are devices generating, routing, processing and detecting single photons which act as information carriers in the field of photonic quantum technologies. In this talk I present recent progress in the development and deterministic fabrication of high-performance single-photon sources and on-chip quantum circuits based on semiconductor quantum dots. Here, quantum dots act as close-to-ideal photon emitters with high quantum efficiency and excellent quantum nature in terms of single-photon purity and photon indistinguishability [1, 2]. Using an advanced nanoprocessing technology platform, deemed in-situ electron beam lithography, we pre-select suitable quantum dots and integrate them with nm accuracy into photonic nanostructures such as microlenses to enhance the brightness of the sources [3], to realize fiber-coupled stand-alone single-photon sources [4, 5], and to enable the development of highly functional quantum circuits [6-8]. The talk gives insight into the physics of such devices and discusses technological challenges, present limitations as well as future prospects of semiconductor quantum dot based quantum devices.

[1] Thoma A. et al., Physical Review. Letters 116, 033601 (2016)
[2] Bounouar S. et al., Physical Review. Letters 118, 233601 (2017)
[3] Gschrey M. et al., Nature Communications 6, 7662 (2015)
[4] Schlehahn A. et al., Scientific Reports 8, 1340 (2018)
[5] Musial A. et al., arxiv:1912.10351 (2019), Advanced Quantum Technologies, in press (2020)
[6] Schnauber P. et al., Nano Letters 18, 2336-2342 (2018)
[7] Mrowiński, P. et al., ACS Photonics, 6, 2231 (2019)
[8] Schnauber P. et al., Nano Letters 19, 7164 (2019)

Einladender: Bratschitsch

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14.05.2020

The electron spin and chiral systems-Merging that results in novel properties

Prof. Dr. Ron Naaman
Department of Chemical and Biological Physics / Weizmann Institute of Science / Israel

Zeit: Donnerstag, 16 Uhr c.t.

Zugangsdaten:
https://wwu.zoom.us/j/93012126842
Meeting-ID: 930 1212 6842
Passwort: WWU_2020

Spin based properties, applications, and devices are commonly related to magnetic effects and to magnetic materials. However, we found that chiral molecules act as spin filters for photoelectrons transmission, in electron transfer, and in electron transport. The spin polarization can exceed 85% at room in some systems.

The new effect, termed Chiral Induced Spin Selectivity (CISS),1,2 was found, among others, in bio-molecules and in bio-systems. It has interesting implications for the production of new types of spintronics devices3,4 in controlling magnetization,5and on electron transfer and conduction. It was also found that charge polarization in chiral molecules is accompanied by spin polarization. This finding shed new light on spin dependent interaction between chiral molecules and between them and magnetic surfaces6.

[1] The Chiral Induced Spin Selectivity Effect, Naaman, R.; Waldeck, D.H. J. Phys. Chem. Lett. (feature), 3, 2178 (2012)

[2] Spintronics and Chirality: Spin Selectivity in Electron Transport Through Chiral Molecules, R. Naaman, D. H. Waldeck Ann. Rev. Phys. Chem., 66, 263 (2015).

[3] Magnetization switching in ferromagnets by adsorbed chiral molecules without current or external magnetic field, O. Ben Dor, S. Yochelis, A. Radko, K. Vankayala, E. Capua, A. Capua, S.-H. Yang, L. T. Baczewski, S. S. P. Parkin, R. Naaman, and Y. Paltiel, Nat. Comm., 8:14567 (2017).

[4] A new approach towards spintronics- spintronics with no magnets, K. Michaeli, V. Varade, R. Naaman, D. Waldeck, Journal of Physics: Condensed Matter, 29, 103002 (2017).

[5] E. Z. B. Smolinsky, A. Neubauer, A. Kumar, S. Yochelis, E.l Capua, R. Carmieli, Y. Paltiel, R. Naaman, K. Michaeli, Electric field controlled magnetization in GaAs/AlGaAs heterostructures-chiral organic molecules hybrids, J. Phys. Chem. Lett. 10, 1139–1145 (2019).

[6] Separation of enantiomers by their enantiospecific interaction with achiral magnetic substrates, K. Banerjee-Ghosh, O. Ben Dor, F. Tassinari, E. Capua, S. Yochelis, A. Capua, S.-H. Yang, S. S. P. Parkin, S. Sarkar, L. Kronik, L. T. Baczewski, R. Naaman, Y. Paltiel, Science360, 1331 (2018).

Einladender: Zacharias

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28.05.2020

2D materials: from atomistic quantum emitters to many-body physics

Prof. Dr. Alexander Holleitner
TU München / Walter Schottky Institut

Zeit: Donnerstag, 16 Uhr c.t.

Zugangsdaten:
https://wwu.zoom.us/j/93012126842
Meeting-ID: 930 1212 6842
Passwort: WWU_2020

We introduce the manifold class of semiconducting 2D materials and their heterostacks, and demonstrate the deterministic generation of single photon emitters in monolayer MoS2 van der Waals heterostacks. The MoS2 is site-selectively bombarded with helium ions to generate optically active defects in arrays and lines on demand. We investigate single defects by performing low temperature photoluminescence and scanning tunneling spectroscopy. Moreover, we show first results on a Bose-Einstein condensate of photogenerated interlayer excitons in MoSe2–WSe2 van der Waals heterostacks.

Figure: Schematic of an atomistic defect in a MoS2-heterostack acting as an on-chip single photon source.
Copyright MCQST and WSI, TUM.

Einladende: Wurstbauer

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02.07.2020

Interplay between superconductivity and spin-dependent fields in nanostructures: Superconductivity meets Spintronics

Dr. F. Sebastián Bergeret
Centro de Física de Materiales, CSIC/UPV, San Sebastián, Spain

Zeit: Donnerstag, 16 Uhr c.t.

Zugangsdaten:
https://wwu.zoom.us/j/93012126842
Meeting-ID: 930 1212 6842
Passwort: WWU_2020

The past decades have witnessed an extraordinary progress in understanding the interplay between superconductivity and magnetism in hybrid devices. Starting in 2001 with the first realisation of ferromagnetic Josephson pi-junctions [1]and the almost simultaneous prediction of triplet superconducting correlations in ferromagnet superconductor structures [2], superconductivity and ferromagnetism are no longer considered as competing phenomena but rather as sources of new emergent states and effects when combined. More recently the field of superconductivity with spin-dependent fields has been extended to the study of topological superconductivity [3] and non-equilibrium effects [4].

In this talk I review the main aspects of superconductivity in the presence of spin-dependent fields, as exchange field and intrinsic spin-orbit coupling (SOC), from a theoretical perspective. I focus on equilibrium effects in hybrid superconducting systems related to the coupling between the singlet and triplet components of the superconducting condensate [5] and its analogy to the charge and spin coupling in normal systems with strong SOC [6], which exhibit the Spin-Hall and the Edelstein (EE) effects [7].

I discuss the counterpart of these magnetoelectric effects in bulk and 2D superconductors as well as in realistic Josephson junctions, by introducing the quantum kinetic equations describing the superconducting state. As an application I discuss the recent realization of a “phase battery” consisting of a semiconducting nanowire embedded into a superconducting loop [8].

[1] V. V. Ryazanov, Phys. Rev. Lett. 86, 2427 (2001).
[2] F. S. Bergeret, A. F. Volkov, and K. B. Efetov, Phys. Rev. Lett. 86, 4096 (2001); Rev. Mod. Phys. 77, 1321 (2005).
[3] M. Sato and Y. Ando, Rep. of Phys. 80, 076501 (2017).
[4] F. S. Bergeret, M. Silaev, P. Virtanen, and T. T. Heikkilä, Rev. Mod. Phys. 90, 041001 (2018); Prog. Surf. Sci. 94, 100540 (2019).
[5] F.S. Bergeret and I. V. Tokatly, Phys. Rev. Lett. 110, 117003 (2013), and Phys. Rev. B 89, 134517 (2014).
[6] V. M. Edelstein, Phys. Rev. Lett. 75, (2004); F. Konschelle, F. S. Bergeret and I. V. Tokatly, Phys Rev. B 92,125443 (2015).
[7] J. Sinova et al, Rev. Mod. Phys. 87, 1213 (2015).
[8] E. Strambini et al, Nature Nanotech. DOI: 10.1038/s41565-020-0712-7

Einladender: Kuhn

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09.07.2020

Die Quantenwelt als Hologramm - angewandte Physik schwarzer Löcher

Prof. Dr. Carlo Ewerz
Universität Heidelberg & EMMI, GSI

Zeit: Donnerstag, 16 Uhr c.t.

Zugangsdaten:
https://wwu.zoom.us/j/93012126842
Meeting-ID: 930 1212 6842
Passwort: WWU_2020

In den letzten Jahren wurden mit Hilfe der Stringtheorie neue, überraschende Verbindungen zwischen Quantenfeldtheorien und höherdimensionalen Gravitationstheorien entdeckt. Diese holographischen Dualitäten verbessern unser Verständnis der fundamentalen Theorien der Natur und haben darüber hinaus zahlreiche Anwendungen. Insbesondere ermöglichen sie eine revolutionär neue Sicht auf stark gekoppelte Quantensysteme in vielen Bereichen der Physik.

Dieser Vortrag soll das Prinzip der holographischen Dualität erklären. Wir werden sehen, wie Eigenschaften stark gekoppelter Quantensysteme durch die Untersuchung schwarzer Löcher in zusätzlichen Raumdimensionen erschlossen werden können. Als Beispiel betrachten wir unter anderem Turbulenz in Supraflüssigkeiten.

Einladende/r: Fachschaft Physik

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