November 2021

Abstracts of the QSIT/Quantum Center, ETH Zurich Lunch Seminar, Thursday, November 4, 2021

Phonon lasing in the quantum regime with mixed-species trapped ions

Tanja Behrle - Trapped Ion Quantum Information Group (Home group), ETH Zurich

Active control of the interaction between a quantum system and its environment, known as quantum reservoir engineering (QRE) has been proven to be a rich resource for quantum state preparation and quantum computation [1, 2]. It also provides the possibility to study open quantum systems, in particular quantum phase transitions driven by dissipation [3{5]. In this talk, I will report on the experimental implementation of QRE on a mixed-species ion crystal consisting of a calcium ion and a beryllium ion. I will show that this allows us to realize a phonon laser [6] and study the lasing phase transition deep in the quantum regime. We also demonstrate phase locking of such a phonon laser, which can nd its application in quantum sensing. Further, we observe the intrinsic dephasing of our phonon laser. The rich toolbox provided by QRE on a mixed-species ion crystal opens the possibility to investigate a non-classical lasing regime in the future in which the system generates squeezed coherent states.

[1] S. Diehl, A. Micheli, A. Kantian, B. Kraus, H. P. Buchler, and P. Zoller, Nature Physics 4, 878 (2008).
[2] F. Verstraete, M. M.Wolf, and J. I. Cirac, Nature Physics 5, 633 (2009).
[3] F. Brennecke, R. Mottl, K. Baumann, R. Landig, T. Donner, and T. Esslinger, Proceedings of the National Academy of Sciences 110, 11763 (2013), http://www.pnas.org/content/110/29/11763.full.pdf.
[4] J. M. Fink, A. Dombi, A. Vukics, A. Wallra, and P. Domokos, Phys. Rev. X 7, 011012 (2017).
[5] T. Fink, A. Schade, S. Hoing, C. Schneider, and A. Imamoglu, 1707.01837v1.
[6] K. Vahala, M. Herrmann, S. Knunz, V. Batteiger, G. Saatho, T. W. Hansch, and T. Udem, Nature Physics 5, 682 (2009).

Integration of MoS₂ Monolayers onto III-V Nanowires into 1D/2D Heterostructures

Valerio Piazza - Laboratory of Semiconductor Materials (Fontcuberta group), EPF Lausanne

Transition metal dichalcogenides (TMDs) are 2D semiconductors characterized by unique features such as layer-dependent direct/indirect band gap transition, high spin-orbit coupling and strain modulation. Depending on the number of layers, their band gap can vary within the visible/near-infrared range making TMDs suitable for a wide variety of optoelectronic applications. Additionally, the possibility to induce the local emission of photons by applying strain is highly beneficial for the design of quantum emitters. In this context, their integration on 1D freestanding nanowires offers an elegant solution to induce localized strain via the dimensionality matching.
In this seminar, I will present the process developed to fabricate hybrid structures composed by MoS₂ monolayers integrated on ordered GaAs nanowire arrays. I will show how the aspect ratio of the underlying nanostructures affects the configuration of the upper ultra-thin layer, which in turn affects the local strain distribution. Atomic force microscopic maps highlight the critical role of the fabrication process. Low temperature Raman spectroscopy on MoS₂ lying on-1D and off-1D evidences the fluctuation of E_12g and A_1g modes associated to the local strain. Finally, we obtained a correlation between the morphology and the optical properties by photoluminescence micromapping.