Temperature degrades entanglement emitted from quantum dots
Two new publications from the Reiter group
Semiconductor quantum dots can generate polarization-entangled photon pairs via the biexciton-exciton cascade. Because the quantum dot is a solid-state object, the interaction with the quantized lattice vibrations, i.e., the phonons, can impair the fidelity of the generated entanglement, in particular at higher temperatures. Therefore, at the moment, quantum dots are operated at liquid helium temperatures (4K). Our studies aim to understand, if generating high- fidelity entanglement from quantum dots with Sterling cooler operating at 30K is feasible.
In one study, published in Nano Letters, together with our experimental colleagues, we studied the influence of dark and hot exciton states on the entanglement fidelity. In our paper we show that these closely lying states can be occupied due to the interaction with phonons, resulting in a severe loss in entanglement fidelity as soon as a thermal occupation becomes possible. In agreement with experiment, we have developed a multi-level model, which can explain both the decay dynamics and the temperature behaviour of the fidelity, revealing that these additional states are indeed detrimental.
In the other study, published in Phys. Rev. B, we consider the entanglement of a continuously driven quantum dots, which depending on the parameter emit different kinds of entangled photons. With phonons, the entanglement is greatly reduced and even vanishes completely. Interestingly, there is a clear point, which marks the transition from entanglement to no-entanglement. The characteristics of this points as function of temperature behaviour can be described by an exponential law akin to a phase transition.
The papers resulted from a collaboration with the theoretical group from Martin Axt from Bayreuth. The experiments in the Nano Letters paper were performed in in the group of Armando Rastelli from Linz and additional calculations were done by Michał Gawełczyk from Wrocław ( ).
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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 South Campus), and from B 1 / A 40 “Dortmund-Dorstfeld” (closer to North Campus). 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 North Campus to South Campus by car, there is the connection via Vogelpothsweg/Baroper Straße. We recommend you leave your car on one of the parking lots at North Campus 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 North Campus. 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 South Campus) Eichlinghofen. The other station is located at the dining hall at North Campus and offers a direct connection to South Campus 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).