Stefan Baeuml
Stefan Baeuml
I am interested in various aspects of entanglement and non-locality. In particular, my research is concerned with the distribution of multipartite entanglement in quantum communication networks. I have also worked on application of non-standard forms of entanglement, such as bound entanglement, to various information theoretical tasks, distribution of entanglement and cryptographic key in quantum networks as well as detection of entanglement in many-body systems.
MY LATEST RESEARCH
Limitations on quantum key repeaters
A major application of quantum communication is the distribution of entangled particles for use in quantum key distribution (QKD). Due to noise in the communication line, QKD is in practice limited to a distance of a few hundred kilometres, and can only be extended to longer distances by use of a quantum repeater, a device which performs entanglement distillation and quantum teleportation. The existence of noisy entangled states that are undistillable but nevertheless useful for QKD raises the question of the feasibility of a quantum key repeater, which would work beyond the limits of entanglement distillation, hence possibly tolerating higher noise levels than existing protocols. Here we exhibit fundamental limits on such a device in the form of bounds on the rate at which it may extract secure key. As a consequence, we give examples of states suitable for QKD but unsuitable for the most general quantum key repeater protocol.
Witnessing entanglement by proxy
Entanglement is relevant for the dynamics of condensed matter properties and quantum computing. The experimental certification of entanglement in macroscopic high temperature systems is constrained by limited access to the quantum state of the system. We show how macroscopic observables such as entropy and temperature can serve as proxy witnesses for entanglement detection without access to local observables. This allows us to certify entanglement at higher temperatures than previous results.
