Welcome to Humboldt University, Berlin

The largest part of the research group around Prof. A. Rauschenbeutel, ErBeStA consortium member and coordinator, moved this summer to Humboldt University of Berlin. Still, TU Wien will remain in the ErBeStA consortium as a project partner. The corresponding efforts there will be led by Dr. Sarah Bayer-Skoff. Here are a few photos of the move to Berlin.

Paper on Slow light-enhanced optical imaging

https://arxiv.org/abs/1905.12383

M. Scheucher, K. Kassem, A. Rauschenbeutel, P. Schneeweiss, and J. Volz

Optical fibers play a key role in many different fields of science and technology. For many of these applications it is of outmost importance to precisely know and control their radius. In this manuscript, we demonstrate a novel technique to determine the local radius variation of a 30 micrometer diameter silica fiber with sub-Angström precision over more than half a millimeter in a single shot, by imaging the mode structure of the fiber’s whispering gallery modes (WGMs). We show that in these WGMs the speed of light propagating along the fiber axis is strongly reduced, which enables us to determine the fiber radius with significantly enhanced precision, far beyond the diffraction limit. By exciting several different axial modes at different probing fiber positions, we verify the precision and reproducibility of our method and demonstrate that we can achieve a precision better than 0.3 Angström. The demonstrated method can be generalized to other experimental situations where slow light occurs and, thus, has a large range of potential applications in the realms of precision metrology and optical sensing.

Quantum Technology: New EU Research Network measures Bell-States

With a 3 million euro endowment, comes a new European research network headed by TU Wien. The goal: a device that can analyze specific entangled quantum states.

The goal is ambitious; develop a novel device that can reliably measure special quantum states known as “Bell-States”. A total of seven research institutes have joined forces to pursue the goal of an optical “Bell-State Analyzer”. The new project is coordinated at Atominstitut of TU Wien, and the European Union is providing a total of 3 million euros of funding.

Quantum Entanglement

An astonishing phenomenon plays a central role in practically all modern quantum technology; quantum entanglement, in which individual particles can no longer be viewed as separate from another. When the state of one particle is measured, this inevitably changes the state of the other particle, meaning the pair can only be described as a single entity.

The degree of entanglement of particles can vary. Two-particle states with the maximum possible degree of entanglement are known as “Bell-States”, named after the Quantum Theoretician, John Bell. In modern quantum technology, Bell-states play an important role and often consist of pairs of photons. Their use spans the fields of quantum teleportation, quantum cryptology, and even quantum sensor technology.

Unfortunately, as of yet, it has not been possible to reliably detect optical Bell-states. Only the state of individual photons can be measured, which however is not the same as measuring entangled quantum states, which simultaneously describe both photons.

New Capabilities through Novel Ideas

New discoveries in recent years have shown that the detection of Bell-states should indeed be possible. With help of a single atom, photon pairs can be manipulated such that their shared state becomes measurable. Thanks to novel methods of nano- fabrication, optical chips may as well allow for the miniaturization of this novel technology.

Still, there remain important scientific and technical problems that need solving, but the path is clear: The project consortium is therefore confident that in the next few years its combined efforts will bring an optical Bell-state analyzer to fruition. The network comprises TU Wien, the Universität Rostock, the University of Nottingham, the Universität Wien, Syddansk Universitet, Aarhaus Universitet, and the Ferdinand-Braun-Institut in Berlin. The project officially started on the July 1st, 2018 and will continue for the next 3 years.