Researchers Create Quantum Light Sources in Atomically Thin Material Layers

Physicists Alexander Holleitner and Jonathan Finley from the Technical University of Munich (TUM) headed an international research team that has effectively placed light sources in atomically thin material layers with a precision of only a few nanometers.

The latest technique enables a host of applications in quantum technologies, ranging from quantum transistors and sensors in smartphones through to novel encryption technologies meant for data transmission.

Former circuits integrated on chips typically depend on electrons as data carriers.In the coming days, photons which transmit data at the speed of light will have the capacity to take on this work in optical circuits. Quantum light sources, which are later linked to quantum fiber optic cables and detectors are required as fundamental building blocks for such kinds of novel chips.

Led by TUM physicists Jonathan Finley and Alexander Holleitner, an international research team has currently succeeded in producing such kinds of quantum light sources in atomically thin material layers and placing them with a precision of just a few nanometers.

First Step Towards Optical Quantum Computers

This constitutes a first key step towards optical quantum computers. Because for future applications the light sources must be coupled with photon circuits, waveguides for example, in order to make light-based quantum calculations possible.

Julian Klein, Study Lead Author and Doctoral Candidate, Technical University of Munich

Here, the exact and accurately controllable placement of the light sources is the crucial point. Quantum light sources could be produced in traditional three-dimensional (3D) materials like silicon or diamond; however, they cannot be accurately placed in these kinds of materials.

Deterministic Defects

Next, the physicists utilized a layer of the semiconductor molybdenum disulfide (MoS₂) as the raw material, which had a thickness of only three atoms. This MoS₂ was subsequently irradiated with a helium ion beam that was focused on a less than 1 nm-surface area.

To produce optically active defects, the required quantum light sources—sulfur or molybdenum atoms—were accurately hammered out of the layer. The detects are traps for what is known as excitons—electron-hole pairs—which subsequently release the required photons.

From a technical standpoint, the latest helium ion microscope installed at the Walter Schottky Institute’s Center for Nanotechnology and Nanomaterials, was very significant for this purpose. The microscope can be used for irradiating materials that have an unprecedented lateral resolution.

On the Road to New Light Sources

Along with theorists at the University of Bremen, TUM, and the Max Planck Society, the researchers created a model that also elucidates the energy states detected at the imperfections in theory.

In the coming days, the scientists are also hoping to produce more intricate light source patterns, in lateral two-dimensional (2D) lattice structures for instance, because this would allow them to study unusual material characteristics and multi-exciton phenomena.

This represents the experimental gateway to a world, which has traditionally been elucidated in theory within the context of what is known as Bose-Hubbard model. This model seeks to factor in intricate processes that take place in solids.

Quantum Sensors, Transistors, and Secure Encryption

There could be advances not only in concept but also with respect to potential technological advancements. Considering that fact that light sources constantly have the same underlying imperfection in the material, they are hypothetically vague. This enables applications that are predicated on the quantum-mechanical principle of entanglement.

It is possible to integrate our quantum light sources very elegantly into photon circuits. Owing to the high sensitivity, for example, it is possible to build quantum sensors for smartphones and develop extremely secure encryption technologies for data transmission.

Julian Klein, Study Lead Author and Doctoral Candidate, Technical University of Munich

The study was supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation), by the TUM International Graduate School of Science and Engineering (IGSSE), by the clusters of excellence “Nanosystems Initiative Munich” (NIM), “Munich Center for Quantum Science and Technology” (MCQST), and “e-conversion,” the TUM Institute for Advanced Study, and the ExQM doctoral program of the Bavarian Elite Network

It was also supported by the European Union in the context of Horizon 2020, the Photonics Research Germany funding program, and the Bavarian Academy of Sciences and Humanities.

Also involved in the study were researchers from the Technical University of Munich, scientists from the Max Planck Institute for Quantum Optics (Garching), the University of Bremen, The State University of New York (Buffalo, USA), and the National Institute for Materials Science (Tsukuba, Japan).