Bright Entanglement via Dark States (BRAIDS)

• Applicant: Professorin Dr. Doris Reiter
• Subject Area: Theoretical Condensed Matter Physics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 560765700

The second quantum revolution is about to transform our world in ways that we can only guess at: Will quantum computers break our communication security? Will they help us design new medication? Will we be able to construct a consistent theory of gravity and quantum physics? Whether one is motivated by futuristic applications or by fundamental questions about nature there is one mystery at the core – quantum entanglement. Being the major difference between classical and quantum physics, entanglement is ultimately responsible for the speedups offered by quantum algorithms and, vice versa, for the difficulty of simulating quantum systems on classical computers. Entanglement keeps a distributed quantum key secure and enables quantum repeaters for global quantum communication. There are many efforts worldwide to build quantum repeaters, and we believe that good sources of single entangled photon pairs will be a key component. In the predecessor project to the present proposal Advanced Entanglement from Quantum Dots (AEQuDot), we made substantial progress towards using single semiconductor quantum dots as sources of single entangled photon pairs. Instead of polarization entanglement, which even in well-engineered quantum dots will probably have limited fidelity, we target time-bin entanglement. In our approach, almost any quantum dot will be able to deliver time-bin entangled photon pairs, which are ideally suited for decoherence-free transmission through optical fibers. The most important game change for our previous and present proposal is to exploit a metastable state for creating single time-bin entangled photon pairs. We have identified dark exciton states as suitable metastable states for this purpose and established new methods to address these states, which are often overlooked. While our collaborative work thus far could not overcome all the challenges towards this goal, it resulted in a number of important theoretical insights and experimental achievements. Most importantly for the present proposal, we developed robust, coherent excitation methods. For the present project Bright Entanglement via Dark States (BRAIDS) we have therefore set ourselves the goal of obtaining efficient production of time-bin entangled photon pairs from a quantum dot via a metastable state.

• DFG Programme: Research Grants
• International Connection: Austria, Poland
• Partner Organisation: Narodowe Centrum Nauki (NCN)
• Cooperation Partners: Dr. Michal Gawelczyk; Professor Dr. Armando Rastelli; Professor Dr. Gregor Weihs