Exploring many-body interactions in one-dimensional dipolar exciton gases defined in atomically thin semiconductors.

• Applicant: Pedro Soubelet, Ph.D.
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 525242381

Semiconductor transition metal dichalcogenides (TMDs) are layered materials that attract the interest of the scientific community due to their promising physical properties, which make them suitable for the study of fundamental science as well as technological applications. Specifically, monolayer TMDs can be stacked at will into van der Waals (vdW) heterostructures with novel electronic or optoelectronic characteristics. This new physics originates in the emergence of strongly correlated quantum phases at the 2D interface between the layers. One of the main objectives in the community is the development of so-called quantum simulators based on vdW heterostructures, an emergent hardware for quantum computation. However, precise stacking of two monolayers over areas beyond a few µm2 is very challenging, mostly due to atomic reconstruction. This is a key drawback in the technological implementation and performance of real devices. This project aims to create a simple and scalable platform for an on-chip optical quantum simulator through the creation of one-dimensional (1D) quantum confined exciton gases in monolayer TMDs. We create the 1D excitons by engineering very large electric field gradients in a substrate of ferroelectric periodically poled lithium niobate (PPLN). 1D geometries enhance quasiparticle correlations and therefore promote the emergence of many-body physics at elevated temperatures in schemes that are potentially simpler to obtain, more robust and reproducible than their 2D counterparts are. Recently, 1D exciton gases in atomically thin TMDs have been predicted to undergo a crossover from a Tonks-Girardeau (TG) to a charge-density-wave (CDW) regime by changing the number of interacting particles in the system. The TG phase is composed of an ensemble of bosonic particles that -like fermions- mimic the Pauli exclusion principle, in a process so-called “fermionization”. The TG phase is of key interest in the development of quantum communication schemes, since this state scales favourably with the particle number operators, enabling the creation of coherent superpositions of strongly interacting bosons that are robust against single-particle loss (NOON states). Importantly, the TG phase shows distinct optical fingerprints that can be readily probed in state-of-the-art experiments. The key objectives of this project are: (i) The design and fabrication of a suitable PPLN substrate to trap 1D excitons in monolayer TMDs. (ii) Probing the ground state properties of 1D confined excitons. (iii) Probing collective phenomena and many body phases of the 1D exciton gas. (iv) Exploring the phase diagram of the system, characterizing each accessible quantum phase and their coherence time. The success of this project will prove the existence of robust many-body quantum correlated phases in 1D exciton gases engineered from 2D TMDs by means of a PPLN substrate. This is a fundamental step towards the creation of an optical on-chip quantum simulator.

• DFG Programme: WBP Position