We offer student projects at all levels, and an overview of the projects is given below.

The project descriptions are ideas for student projects, but if you have your own idea for a project, please feel free to contact any member of our group.

Some of the projects can be carried out both as BSc and MSc projects, and the contents of any of the projects will be planned together with the student.

Press the project titles to find detailed descriptions and contact information.

You can also have a look at reports from previous student projects in our group in the menu to the right.

Each semester, we offer a number of "Fagprojekter" (course 34029) for second-year students in the Physics and Nanotechnology BSc-program; You can find the project descriptions at the course homepage.

**Quantum Photonic Devices with Ultimate Design Precision**

This project in collaboration with DTU Fotonik and Nanotech aims at the realization of a new platform based on 2D nanostructures for the making of novel atomically precise devices for quantum technologies.

**Theory of Single Photon Sources**

The overall aim of this project is to establish a theoretical understanding of the physical mechanisms governing light emission in semiconductor QDs, and ultimately develop improved SPS. This may be tackled through two avenues with significant overlap: through optical simulations novel photonic structures will be proposed to maximise the efficiency of SPS; by developing microscopic theories of QD emission in photonic structures, new approaches for enhancing photon indistinguishability will be investigated.

**Theory of quantum effects in nanolasers**

In this project we will investigate the role of superradiance in nanolasers, which is a current hot topic within laser physics [1]. We have recently developed an analytical theory accounting for some of the important superradiant effects occurring in lasers [2], but in this project the aim is to develop a more comprehensive model of the phenomenon, including quantum mechanical Monte Carlo simulations. We also wish to apply the model to the actual case of photonic crystal nanolasers, which can be fabricated at DTU Fotonik.

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**Stochastic modelling of nanolasers**

The purpose of this project is to develop and analyze a theoretical model of quantum noise in nanolasers and to use the model to get fundamental insight into the physics of such nanolasers. Furthermore, the model will be used to analyze different types of laser structures, with the purpose of guiding experimental work.

**Devices for on-chip quantum information technology**

This project will investigate how photons interact with quantum dots in semiconductor cavity QED systems. The goal is to theoretically design and characterize a simple device for quantum information technology such as a controlled few-photon gate [3], a controlled photon switch, or a multi-photon entanglement protocol.

All quantum systems - from single atoms and quantum dots to microcavities and nano-mechanical resonators - interact with their surrounding environment and are thus *open*. This interaction leads to decoherence, which drives coherent quantum dynamics towards classical behavior. Thus, to combat decoherence, understanding open quantum systems is necessary. We offer a number of projects on understanding the role of phonon interactions, nuclear spin dynamics, and surrounding photonic structures on quantum dots.

**Photonic crystal Fano lasers**

The Fano laser has recently provided exciting results, including the first report of self-pulsing in microscopic lasers. In this project a modified Fano laser structure will be investigated, which bridges the gap between conventional line-defect lasers and the Fano laser, in order to combine the desirable properties of both laser devices. This is an open project with opportunities in both theory, numerical modelling, and experimental work, depending on student interest and background.

**Dual Fano resonances for high speed optical communication**

In this project you will be investigating a cavity-waveguide system based on a photonic crystal membrane platform, which supports two Fano resonances. One resonance will be used for controlling the other resonance. The steep slope of Fano resonances makes it possible to realise extremely efficient all-optical switching on a photonic chip. The Fano resonance has previously lead to experimental demonstrations of ultrafast optical switches and self-pulsing nano lasers.

**All-optical phase modulators using coupled-photonic crystal cavities**

In this project, ultra-compact high-speed and low-energy optically controlled phase modulators will be designed. Starting from the fundamental understanding of a cavity-wavegiode system, a numerical model based on coupled mode theory will be developed. Depending on interest and progress, proof of concept experimental investigations will be carried out.

**Nano-fabrication of Quantum Photonic Devices**

This project aims at processing crystal phase quantum dots in nanowires to propose new device designs for quantum photonic applications. This will be done using our state of the art clean room facility.

**Quantum Gates Experiments and/or Modelling**

The aim of this project is to create quantum gates. Quantum gates are one of the key building blocks of forthcoming quantum computers. For instance, they can be used to entangle qubits.

**Fast Single Photons**

Can single photons travel faster than c, the speed of light?Fast" light, or light that goes faster than it should, is a well known phenomenon for laser light and it does not contradict special relativity. But what about single photons? There are still debates on if single photons can travel faster than light, and if possible, on whether or not we can actually measure them. We have clear experimental evidence that show faster-than-light single photons and we want to understand the physics behind these results and create a model that can replicate them.

Nanowire quantum dots are one of the new big player in quantum technologies and many game-changer devices, like quantum gates or quantum memories, still need to be designed! We have the tools to design, to fabricate and to test novel structures in order to make such devices, but first we need to simulate them using our post-Hartree-Fock based model to understand which semiconductor structure could be the next-step device in quantum information.

Can we use quantum mechanics to achieve communication 100% secure against eavesdropping? In this project, we will develop an experimental setup to send encrypted messages using EPR Quantum Key Distribution. Multiple existing protocols will be studied and one of them will be chosen for implementation in our lab, starting from scratch.

**qLab towards the Quantum Internet**

Modern communication networks, such as the Internet, are not 100% secure against eavesdropping nor energy efficient. Our vision is to develop a solid ground from which to design a novel network based on quantum technologies. This Quantum Network will allow secure and energy-efficient communication and will make possible for quantum computers to communicate in their own quantum language. We believe this can be done using semiconductor structures like quantum dots in nanowires.

In this project a mathematical model for the Fano laser will be formulated and used to investigate, numerically and analytically, the fundamental laser properties. An important goal of the project is to investigate the aspects of the laser design that are critical for experimental implementations.

**Multi-photon processes in solid-state quantum emitters**

Though quasi-resonant excitation schemes are common, they are still not fully understood, and have only recently begun to be investigated experimentally. DTU Fotonik has strong collaborations with experimental and theoretical groups fabricating single photon sources. The aim of this theoretical project is to better understand the quasi-resonant excitation procedure and its relation to multi-photon processes.

**Quantum Photonic Devices with Ultimate Design Precision**

This project in collaboration with DTU Fotonik and Nanotech aims at the realization of a new platform based on 2D nanostructures for the making of novel atomically precise devices for quantum technologies.

**Theory of Single Photon Sources**

The overall aim of this project is to establish a theoretical understanding of the physical mechanisms governing light emission in semiconductor QDs, and ultimately develop improved SPS. This may be tackled through two avenues with significant overlap: through optical simulations novel photonic structures will be proposed to maximise the efficiency of SPS; by developing microscopic theories of QD emission in photonic structures, new approaches for enhancing photon indistinguishability will be investigated.

**Theory of quantum effects in nanolasers**

In this project we will investigate the role of superradiance in nanolasers, which is a current hot topic within laser physics [1]. We have recently developed an analytical theory accounting for some of the important superradiant effects occurring in lasers [2], but in this project the aim is to develop a more comprehensive model of the phenomenon, including quantum mechanical Monte Carlo simulations. We also wish to apply the model to the actual case of photonic crystal nanolasers, which can be fabricated at DTU Fotonik.

**Stochastic modelling of nanolasers**

The purpose of this project is to develop and analyze a theoretical model of quantum noise in nanolasers and to use the model to get fundamental insight into the physics of such nanolasers. Furthermore, the model will be used to analyze different types of laser structures, with the purpose of guiding experimental work.

**Devices for on-chip quantum information technology**

This project will investigate how photons interact with quantum dots in semiconductor cavity QED systems. The goal is to theoretically design and characterize a simple device for quantum information technology such as a controlled few-photon gate [3], a controlled photon switch, or a multi-photon entanglement protocol.

All quantum systems - from single atoms and quantum dots to microcavities and nano-mechanical resonators - interact with their surrounding environment and are thus *open*. This interaction leads to decoherence, which drives coherent quantum dynamics towards classical behavior. Thus, to combat decoherence, understanding open quantum systems is necessary. We offer a number of projects on understanding the role of phonon interactions, nuclear spin dynamics, and surrounding photonic structures on quantum dots.

**Fabrication and experimental charactarization of photonic crystal lasers with buried heterostructure**

The aim of this project is to tailor and optimize the fabrication process and design of the BH PhC semiconductor lasers in order to achieve high-performance and efficiency operation. Three major parts constitute the fabrication process of the laser device: epitaxial growth and direct wafer bonding, the formation of the buried heterostructure region and regrowth, aligned transfer of photonic crystal pattern and membranization. After the completion, the experimental characterization is carried out inside the in-house optical lab, and the fabrication process is re-iterated based on the acquired information.

**Photonic crystal Fano lasers**

The Fano laser has recently provided exciting results, including the first report of self-pulsing in microscopic lasers. In this project a modified Fano laser structure will be investigated, which bridges the gap between conventional line-defect lasers and the Fano laser, in order to combine the desirable properties of both laser devices. This is an open project with opportunities in both theory, numerical modelling, and experimental work, depending on student interest and background.

In this project you will be investigating a cavity-waveguide system based on a photonic crystal membrane platform, which supports two Fano resonances. One resonance will be used for controlling the other resonance. The steep slope of Fano resonances makes it possible to realise extremely efficient all-optical switching on a photonic chip. The Fano resonance has previously lead to experimental demonstrations of ultrafast optical switches and self-pulsing nano lasers.

In this project, ultra-compact high-speed and low-energy optically controlled phase modulators will be designed. Starting from the fundamental understanding of a cavity-wavegiode system, a numerical model based on coupled mode theory will be developed. Depending on interest and progress, proof of concept experimental investigations will be carried out.

**Nano-fabrication of Quantum Photonic Devices**

This project aims at processing crystal phase quantum dots in nanowires to propose new device designs for quantum photonic applications. This will be done using our state of the art clean room facility.

**Quantum Gates Experiments and/or Modelling**

The aim of this project is to create quantum gates. Quantum gates are one of the key building blocks of forthcoming quantum computers. For instance, they can be used to entangle qubits.

**
Fast Single Photons
**Can single photons travel faster than c, the speed of light?Fast" light, or light that goes faster than it should, is a well known phenomenon for laser light and it does not contradict special relativity. But what about single photons? There are still debates on if single photons can travel faster than light, and if possible, on whether or not we can actually measure them. We have clear experimental evidence that show faster-than-light single photons and we want to understand the physics behind these results and create a model that can replicate them.

**Quantum information technology with quantum dots in nanowire
**Nanowire quantum dots are one of the new big player in quantum technologies and many game-changer devices, like quantum gates or quantum memories, still need to be designed! We have the tools to design, to fabricate and to test novel structures in order to make such devices, but first we need to simulate them using our post-Hartree-Fock based model to understand which semiconductor structure could be the next-step device in quantum information.

**Quantum Cryptography: 100% secure communication
**Can we use quantum mechanics to achieve communication 100% secure against eavesdropping? In this project, we will develop an experimental setup to send encrypted messages using EPR Quantum Key Distribution. Multiple existing protocols will be studied and one of them will be chosen for implementation in our lab, starting from scratch.

** qLab towards the Quantum Internet
**Modern communication networks, such as the Internet, are not 100% secure against eavesdropping nor energy efficient. Our vision is to develop a solid ground from which to design a novel network based on quantum technologies. This Quantum Network will allow secure and energy-efficient communication and will make possible for quantum computers to communicate in their own quantum language. We believe this can be done using semiconductor structures like quantum dots in nanowires.

In this project a mathematical model for the Fano laser will be formulated and used to investigate, numerically and analytically, the fundamental laser properties. An important goal of the project is to investigate the aspects of the laser design that are critical for experimental implementations.

**Preventing a system from going classical: The quantum Zeno effect**

The quantum Zeno effect is weird: If a system is observed it does not change! Quantum mechanically, an observation collapses the wavefunction onto a specific state, and if the observations are made frequently enough, the system will not evolve away from that initial state. The effect has been experimentally observed in cold atoms, but here we aim to understand what the conditions are for observing it in a quantum dot.

**Experimental characterization of slow light enhanced photonic crystal optical amplifiers**

The semiconductor optical amplifier is a key component for any optical network, however, for use in an integrated platform, downscaling the required size footprint is of major importance. The aim of this project is to experimentally investigate the fundamental as well as practical limits for achieving enhanced amplification using photonic crystal waveguide based optical amplifiers that exploit slow light effects.

Though quasi-resonant excitation schemes are common, they are still not fully understood, and have only recently begun to be investigated experimentally. DTU Fotonik has strong collaborations with experimental and theoretical groups fabricating single photon sources. The aim of this theoretical project is to better understand the quasi-resonant excitation procedure and its relation to multi-photon processes.

**Phonon effects in a nanowire single-photon source**

Semiconductor nanowires containing quantum dots are interesting candidates for single-photon sources, which constitute a major building block in the realization of quantum computers. In this project we employ advanced quantum mechanical models and develop numerical tools to examine, how the functionality of the single-photon source may be improved by minimizing the disturbances from the environment.

**Optical properties of photonic crystal microcavities and waveguides**

In quantum information technology there is a need for devices that can generate a stream of single photons, which may be used as qubits in quantum computers. We study the fundamental properties of semiconductor single-photon sources constructed by placing a quantum dot in a nanowire or a photonic crystal cavity.

Extracting Beta-factor of a photonic crystal laser (Fagproject, 2016, Jonas Bach Olsen and Frederik Diethelm Jacobsen)

Optical Quantum Gates in Nanowires (BSc project, 2015, Nicklas Larsen and Jakob Ravnskjær)