Atomic Quantum Emitters in 2D Frameworks

Project Information

AQE2D

Grant agreement ID: 948243

DOI

10.3030/948243

EC signature date 4 September 2020

Start date 1 October 2021

End date 30 September 2026

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 2 139 400,00

EU contribution

€ 2 139 400,00

Coordinated by

EIDGENOSSISCHE MATERIALPRUFUNGS- UND FORSCHUNGSANSTALT
Switzerland

Periodic Reporting for period 2 - AQE2D (Atomic Quantum Emitters in 2D Frameworks)

Reporting period: 2023-04-01 to 2024-09-30

Summary of the context and overall objectives of the project

Lattice imperfections in solids, such as missing or foreign atoms, are of significant technological importance for instance as light emitters in laser gain media or dopants in semiconductors. The advent of quantum science and technology triggered yet another wave of interest for utilizing these imperfections as a building block for quantum sensing, communication and information processing. Due to strong confinement of atomic objects, they feature large characteristic energy scales that render their quantum properties particularly robust.

Yet, as device miniaturization reaches atomic length scales, exact positioning of defects become critical to precisely control the interaction between them. Moreover, material interfaces that could lead to decoherence of quantum states become increasingly relevant. Two-dimensional (2D) materials offer key advantages in addressing these challenges. They enable atomically precise engineering of quantum defects with positional control and provide van der Waals interface devoid of dangling bonds. Recent breakthroughs in 2D material synthesis and ultrafast single-atom-resolving probes have made it possible to generate and characterize atomic-scale designer quantum states with unprecedented precision.

In the AQE2D project, our objective is to explore the fundamental physical properties of single defects in 2D materials, including their electronic, spin, and optical degrees of freedom, on their intrinsic length, time, and energy scales. This requires a new type of instrument with simultaneous atomic spatial, picosecond temporal, and millielectronvolt energy resolution. By developing an ultrafast lightwave-driven scanning tunnelling microscope using single-cycle THz pulses as ultrafast voltage transients, we will measure the excitation dynamics at single defects in 2D materials with unprecedented resolution in both time and space. This innovative tool will open new frontiers in the spatiotemporal characterization of low-dimensional condensed matter systems.

The atomic-precision functionalization of 2D materials is also a key technology for other high impact areas where 2D materials currently challenge old device paradigms, for instance in transport, optoelectronics, and catalysis. Hence, the outcome of this project will influence developments in areas well beyond the scope of quantum information science.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

In the first half of the project, we have successfully setup the THz-STM lab featuring a commercial low-temperature scanning probe microscope and a custom optical setup. The latter features a femtosecond fiber laser with high repetition rate, various home-built modules for THz pulse generation, THz waveform shaping and detection, and an optical spectrometer. The development of this state-of-the-art ultrafast STM marks a significant achievement in this project. Our experiments demonstrated THz-driven tunnelling currents in bulk metals and semiconducting 2D materials as a function of THz field amplitude and THz phase. Through near-field waveform sampling and precise amplitude calibration, we gained the capability to selectively access specific defect orbitals and dispersive band states in 2D semiconductors.

In collaboration with experts from the Center for 2D Layered Materials at Pennsylvania State University, we developed strategies to introduce dopants into semiconducting 2D transition metal dichalcogenides (TMDs), such as MoS2, WS2, and WSe2, during synthetic growth. Through detailed characterization, we gained insights into the structural, electronic, and magnetic properties of these single dopants, including carbon-hydrogen complexes, vanadium, and rhenium. Notably, we discovered the stabilization of spin states in vanadium dimers and the atomically-precise activation of carbon radical ions in certain TMDs. Currently, we are developing THz pump-THz probe schemes to probe ultrafast charge, spin, and exciton dynamics on these TMD defect systems.

The project team has actively disseminated their research findings through various channels. The PI delivered seven invited conference talks and research seminars, while group members presented 18 contributed talks and posters at international conferences and workshops. Additionally, the PI co-organized a four-day symposium at the MRS Spring Meeting 2022, along with a one-day satellite workshop of the MRS Quantum Staging Group. These events facilitated collaboration and knowledge exchange among experts in solid-state spin defects and 2D materials science.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

We have achieved significant progress beyond the current state of the art in controlling the charge state of single defects in TMDs. This control is facilitated by choice of the impurity (electron configuration), engineering the work function of the substrate, and controlling the proximity between defects. The charge state, in turn, governs the spin state and optical emission properties of these defects. Furthermore, we successfully resolved the electron-phonon coupling at a carbon radical ion, which we identified as a prime candidate for an atomic quantum emitter in TMDs.

A key technical advancement of our project is the development of an ultrafast THz-STM. This ground-breaking instrument enables us to investigate the temporal evolution of excited states associated with single defects in TMDs. Operating at megahertz repetition rates and generating electron-volt scale voltage transients in the STM junction, this instrument sets new standards in the field. By implementing flexible waveform shaping and near-field sampling techniques, we have unlocked a previously unexplored regime of spatio-temporal characterization of low-dimensional materials. We aspire to produce seminal publications that will shape this emerging field.

Charge-state dependent symmetry breaking of substitutional Re atoms in MoS2

THz-STM Lab at Empa

State-selective tunneling of THz transients into MoS2 bands and defect states