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Growth and Functional Properties of Ultrapure Nanomaterials

Growth of novel materials and hetero-interfaces: Underlying almost all of the science we do at SNQS is the availability of precise nanostructures created by design using controlled synthesis methods. We employ high-purity molecular beam epitaxy (MBE) dedicated to III-V compound semiconductors (group-III arsenides & antimonides), group-III nitrides and, most recently, ultra-pure 2D materials and their heterostructures. Currently, a substantial effort in synthesis is on III-V nanowires (NW), which offer unique capabilities in heterostructure and crystal phase engineering, as well as site-selective growth and deterministic incorporation of atomically engineered low-dimensional quantum systems.
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Nanowire Nanolasers: Semiconductor lasers promise to have improved performance and novel properties as their physical size is scaled down to the quantum limit for electrons and photons. One of the major research directions at SNQS focuses on developing high-performance integrated (quantum)photonic and optoelectronic devices based on monolithically integrated nanowires (NWs). Specific examples include NW-based lasers and non-classical single photon emitters based on NW-QD devices. Hereby, an important task is to explore the optical and photonic responses of the respective systems using advanced confocal luminescence spectroscopy, where e.g. the effects of the quantized electronic structure, light-matter interactions, or the coupling of light to on-chip photonic circuits are explored.
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2D-Materials and their Heterostructures

Spin and Magneto-Optical Phenomena: The optical properties of 2D transition-metal dichalcogenides (TMDs) such as MoSe2 or WS2, are dominated by excitons, Coulomb-bound particles comprised of an electron and a hole each of which possesses a spin and valley quantum number. Because 2D materials are so thin materials directly adjacent to the TMD layer can influence spin and magneto-optical properties. SNQS researchers are interested in questions like: What are the fundamental spin- and excitonic-excitations in TMDs? How does the dielectric / magnetic / topological environment influence the excitons?


Localized excitons in 2D-materials: Localized excitons in 2D materials have shown to be sources of non-classical light. SNQS researchers follow three avenues for exciton localization: (i) dielectric engineering, (ii) strain-induced exciton localization and (iii) site-selective generation of native defects via He-ion irradiation. Our goals are to understand the mechanisms of localization for couple light from such localized emitters into photonic structures and explore interesting phases of interacting excitations in defined trapping potentials. Here, we work closely with the Ultrafast Optoelectronics group led by Alexander Holleitner at WSI, the Experimental Semiconductor Physics group led by Ian Sharp and the Photonic Quantum Engineering group at TUM-ECE led by Kai Müller.
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Novel heterostructures with 2D perovskites: Similar to conventional III-V semiconductor superlattices, Ruddlesden-Popper halide perovskites are quantum well-like structures formed by two-dimensional layers of halide perovskites semiconductors, separated by organic spacer layers. This layered structure can be tuned by varying the perovskite layer thickness and the composition of the organic layer. Although efficient opto-electronic devices were made from such materials, fundamental questions concerning the nature of optical resonances remain. SNQS researchers strive to understand how the optical properties of these fascinating materials can be controlled, especially when they are combined with other 2D-materials.
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Quantum Optics of Solids

Quantum optics and spin-photon interfaces in single and coupled-QDs: SNQS researchers investigate quantum optical methods to prepare, manipulate and readout optically active quantum spin-states in semiconductor QDs. Due to their strong optical transitions with almost transform-limited linewidth, QDs are ideal prototypes for solid-state quantum emitters. Among our current experiments are resonance fluorescence investigations of quantum optical properties of QDs, investigations of the complex dynamics of single electron and hole spins confined to QDs and the use of QD-molecules for solid-state quantum repeaters. SNQS works closely with the Photonic Quantum Engineering group at TUM-ECE led by Kai Müller.
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Diamond Quantum Optics: Diamond is well known to host interesting spin-centers with strong optical activity and coherent spin dynamics up to elevated temperatures. Besides the well-studied NV-center, other color centers such as SiV, GeV and SnV have recently moved into focus by virtue of their excellent quantum optical properties at low-temperatures. However, diamond is difficult to nano-pattern to enhance the light-matter coupling towards the deterministic limit. Here, SNQS researchers work on patterning diamond containing quantum emitters and their use for the generation of photonic cluster states for quantum communication. SNQS works closely with the Photonic Quantum Engineering group and the Chair of Theoretical Information Technology at TUM-ECE.
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Quantum Photonics

Photonic crystal nanostructures: Photonic crystals consist of regularly patterned arrays of materials with different dielectric constants, giving rise to a band structure for light. In particular, one and two-dimensional photonic crystal nanostructures provide a platform for integrated quantum-photonics including nano-cavities, waveguides, splitters and interferometers and allow the exploration of chiral and non-commensurate states of light. We study light-matter-interactions between discrete quantum emitters and tailored optical modes in photonic nanomaterials with topics linking fundamental quantum optics to sensing and metrology.
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Optics at the nanoscale: Focusing electromagnetic fields form far field to nanoscale dimensions is one of the central research goals in nanooptics. While conventional diffractive optics are limited by the Abbé diffraction limit, metal optics offers routes to concentrate far-field radiation into volumes of only a few cubic nanometers and as a result of that give rise to extraordinarily enhanced electromagnetic near-fields.
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Quantum Sensing and Metrology

On-chip single photon detectors: Patterned superconducting thin films have recently been exploited for realizing high-efficiency, ultra-fast and broadband photon detectors with the capability to detect light down to the single photon level. We are working closely with the company Kiutra GmbH and the group of Kai Müller to realize superconducting nanowire single photon detectors for emergent quantum technologies.
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Optics at the nanoscale: Focusing electromagnetic fields form far field to nanoscale dimensions is one of the central research goals in nanooptics. While conventional diffractive optics are limited by the Abbé diffraction limit, metal optics offers routes to concentrate far-field radiation into volumes of only a few cubic nanometers and as a result of that give rise to extraordinarily enhanced electromagnetic near-fields.
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