AG Jun. Prof. Dr. Marc Aßmann
Semiconductor Quantum Optics
Our experimental group works in the field of semiconductor quantum optics, which is a novel and innovative topic at the interface between solid state physics and quantum optics. Traditionally, quantum optics deals with the interaction of quantized light fields with systems such as dilute gases at temperatures close to absolute zero temperature. When trying to transfer these quantum information technologies to a more application-friendly semiconductor setting, additional difficulties and challenges arise:
Coherence times in semiconductor systems are typically three orders of magnitude smaller compared to their atomistic counterparts, all atoms share exactly the same characteristics, while tailored and engineered semiconductor structures may show deviations from each other and carriers in semiconductors are always subject to interactions with the many-body host crystal surroundings, while cold atoms may be kept and investigated in vacuum.
Our group develops spectroscopic techniques and experimental strategies suitable for the demanding challenges of studying quantum optical phenomena in a semiconductor surrounding. Some of the topics we currently study are given below.
Ultrafast Photon Number Statistics
The photon number distribution of a light field yields precise information about its properties. However, measuring the photon number statistics appropriately requires a temporal resolution better than the coherence time of the light field. For semiconductor light sources, this timescale may be as short as few picoseconds, which renders standard approaches from cold atom physics problematic. We have developed a streak camera technique that is able to monitor individual photon detection events with a temporal resolution of 2 picoseconds. This technique has a wide range of applications, ranging from a precise characterization of lasing thresholds to investigating correlated photon emission.
Continuous Variables and Semiconductors Light Sources
Besides the photon number, also the phase properties of light fields are of central interest. These are typically studied using continuous variables in phase space by means of homodyne detection. A stable phase reference, the so-called local oscillator, forms the basis of this experimental technique. For most electrically or non-resonantly pumped semiconductor light sources, such a phase reference is not available. We develop special multiport homodyne detection techniques that allow us to acquire phase-space information even in the absence of a well-defined phase reference.
Optically Imprinted Circuits
Non-resonant optical excitation of a semiconductor creates free electrons and holes, which interact with other particles. For example, they provide a repulsive potential for exciton-polaritons, mixed light-matter quasiparticles with extremely small mass. By spatially tailoring the shape of a laser spot, we are able to engineer functional potential landscapes for polaritons, which enable us to create reconfigurable optically imprinted circuits. Examples of functional elements already realized include elements changing the path of traveling polaritons and polariton amplifiers. Further, effective manipulation of their polarization and orbital angular momentum properties is one of our focus topics.
Current offers for Bachelor-, Master- or PHD-theses
Please contact Marc Aßmann if you are interested in thesis work on these topics.
- Jun.-Prof. Dr. Marc Aßmann
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Location & approach
The campus of TU Dortmund University is located close to interstate junction Dortmund West, where the Sauerlandlinie A 45 (Frankfurt-Dortmund) crosses the Ruhrschnellweg B 1 / A 40. The best interstate exit to take from A 45 is "Dortmund-Eichlinghofen" (closer to Campus Süd), and from B 1 / A 40 "Dortmund-Dorstfeld" (closer to Campus Nord). Signs for the university are located at both exits. Also, there is a new exit before you pass over the B 1-bridge leading into Dortmund.
To get from Campus Nord to Campus Süd by car, there is the connection via Vogelpothsweg/Baroper Straße. We recommend you leave your car on one of the parking lots at Campus Nord and use the H-Bahn (suspended monorail system), which conveniently connects the two campuses.
TU Dortmund University has its own train station ("Dortmund Universität"). From there, suburban trains (S-Bahn) leave for Dortmund main station ("Dortmund Hauptbahnhof") and Düsseldorf main station via the "Düsseldorf Airport Train Station" (take S-Bahn number 1, which leaves every 20 or 30 minutes). The university is easily reached from Bochum, Essen, Mülheim an der Ruhr and Duisburg.
You can also take the bus or subway train from Dortmund city to the university: From Dortmund main station, you can take any train bound for the Station "Stadtgarten", usually lines U41, U45, U 47 and U49. At "Stadtgarten" you switch trains and get on line U42 towards "Hombruch". Look out for the Station "An der Palmweide". From the bus stop just across the road, busses bound for TU Dortmund University leave every ten minutes (445, 447 and 462). Another option is to take the subway routes U41, U45, U47 and U49 from Dortmund main station to the stop "Dortmund Kampstraße". From there, take U43 or U44 to the stop "Dortmund Wittener Straße". Switch to bus line 447 and get off at "Dortmund Universität S".
The AirportExpress is a fast and convenient means of transport from Dortmund Airport (DTM) to Dortmund Central Station, taking you there in little more than 20 minutes. From Dortmund Central Station, you can continue to the university campus by interurban railway (S-Bahn). A larger range of international flight connections is offered at Düsseldorf Airport (DUS), which is about 60 kilometres away and can be directly reached by S-Bahn from the university station.
The H-Bahn is one of the hallmarks of TU Dortmund University. There are two stations on Campus Nord. One ("Dortmund Universität S") is directly located at the suburban train stop, which connects the university directly with the city of Dortmund and the rest of the Ruhr Area. Also from this station, there are connections to the "Technologiepark" and (via Campus Süd) Eichlinghofen. The other station is located at the dining hall at Campus Nord and offers a direct connection to Campus Süd every five minutes.
The facilities of TU Dortmund University are spread over two campuses, the larger Campus North and the smaller Campus South. Additionally, some areas of the university are located in the adjacent "Technologiepark".
Site Map of TU Dortmund University (Second Page in English).