The MCQST Colloquium Series features interdisciplinary talks given by visiting international speakers. The monthly colloquium covers topics spanning all MCQST research units and will be broadcast live via Zoom for audiences worldwide. The main goal of the series is to create the framework for idea exchange, to strengthen links with QST leading groups worldwide, as well as to act as an integral part of the local educational environment.

MCQST Colloquium: X-mas edition with MCQST members Lode Pollet and Elena Blundo

We are excited to invite you to the colloquium talks by Lode Pollet (LMU) and Elena Blundo (WSI - TUM).

Agenda

14:00 | Colloquium talk by Lode Pollet (LMU) on "The spin liquid on the ruby lattice induced by the Rydberg blockade mechanism"

14:45 | Colloquium talk by Elena Blundo (WSI - TUM) on “Unveiling new excitons in two-dimensional heterostructures”

15:30 | Get-togehter and exchange with coffee, plätzchen & glühwein

The spin liquid on the ruby lattice induced by the Rydberg blockade mechanism | Lode Pollet (LMU)

One of the unique features in the emerging field of Rydberg quantum many-body physics is the Rydberg blockade mechanism, which is the prevention of the excitation of a second Rydberg atom situated closely to an already excited Rydberg atom.

I comment on a recent experiment from Harvard which exploited this mechanism in order to observe the onset of a dynamically prepared, gapped Z2 quantum spin liquid on the ruby lattice (Semgehini et al, Science 374, 1242 (2021)). Quantum spin liquids are exotic states of quantum matter which defy magnetic ordering down to the lowest temperatures but have a topological and emergent lattice gauge structure instead. They have been intensely sought after for the past 30 years, yet escaped experimental detection. The thermodynamic properties of models relevant to the Harvard experiment remain inadequately addressed, yet knowledge thereof is indispensable if one wants to prepare large, robust, and long-lived quantum spin liquids. Using large scale quantum Monte Carlo simulations, we find in the PXP model a renormalized classical spin liquid with constant entropy density approaching log(2)/6 in the thermodynamic limit for all moderate and large values of the detuning. This is seen starting from temperatures of the order of the Rabi frequency down to the lowest temperatures we could simulate, which are about 100 times lower. With the experimentally relevant Van der Waals interactions, constant entropy plateaus are still found, but their value shifts with the detuning. I comment on the adiabatic approximation to the dynamical ramps for the electric degrees of freedom, and the magnitude of the observed string parity order parameters, which leads to a re-interpretation of the Harvard experiment.

Ref. Z. Wang and L. Pollet, arXiv:2406.07110 (2024)

About Lode Pollet
Lode Pollet studied civil engineering, option physics at the University of Gent, Belgium, where he also obtained his PhD in theoretical physics in 2005, focusing on condensed matter aspects of ultracold atomic gases. Following postdocs at ETH Zurich with Matthias Troyer, UMass Amherst with Nikolay Prokof'ev and Boris Svistunov, and Harvard with Eugene Demler, he joined the LMU physics department in October 2011 where he obtained tenure in 2015. His awards include an ERC starting and consolidator grant, he was co-winner of the Newcomb-Cleveland prize 2010-2011 and is a member of the Wilczek Quantum Center. His research interests include quantum Monte Carlo simulations, strongly-correlated many-body systems, supersolidity, first-principles calculations of ultracold atomic systems, disordered systems, quantum phase transitions, quantum spin liquids, quantum simulation, quantum computation and machine learning.

Unveiling new excitons in two-dimensional heterostructures | Elena Blundo (WSI - TUM)

Van der Waals (vdW) two-dimensional (2D) materials can be stacked with unprecedented flexibility to create heterostructures (HSs), offering extra degrees of freedom such as arbitrariness in the choice of the materials, and the twist angle between the constituent materials. Whenever 2D materials are stacked with a non-null twist angle, a periodic pattern, referred to as moiré pattern, is created. In semiconducting HSs made of transition metal dichalcogenides (TMDs, such as MoSe2 and WSe2), this results in the creation of a moiré potential that can trap interlayer excitons (electron-hole pairs with the electron and the hole lying in the two different constituent materials of the HS). Moiré-localised interlayer excitons, or moiré excitons (MXs), have shown promise, e.g., for the formation of Bose-Einstein condensates and highly correlated exciton states, or for the creation of nanoscale-ordered quantum emitters. In this talk, the optoelectronic properties and thermal stability of MXs will be discussed. By focusing on MoSe2/WSe2 HSs with nearly 0◦ twist angle, we first unveil how excitons localised in different moiré minima corresponding to different atomic registries may coexist. Additionally, we show how the exciton dynamics and emission lineshape evolution with temperature reveal clear signatures that MXs de-trap from the moiré potential and turn into free interlayer excitons for temperatures above 100 K. Finally, we discuss the potentiality of such HSs for quantum applications.

About Elena Blundo
Elena Blundo studied Physics at Sapienza, University of Rome, where she also got her PhD in 2023. During her Master’s degree and PhD, she carried out her research in the group of Prof. Antonio Polimeni, where she investigated the optoelectronic properties of nanostructures and especially of two-dimensional (2D) materials. Her studies were mainly focused on unveiling the effects of strain on the optoelectronic, mechanical and vibrational properties of 2D semiconductors. In 2024, Elena Blundo became a MCQST Distinguished Postdoc fellow at the Walter Schottky Institute of the Technical University of Munich. Therein, she is exploring new strategies to achieve controllable quantum emitters in 2D heterostructures.

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Meeting-ID: 614 2637 2835, Passcode: mcqst2025