What we can and what we can't say about employment growth in specialised cities

There is an ongoing debate on whether certain sector structures enhance regional employment growth. Often, regional policies promote clusters and, hence, regional specialisation. It is commonly believed that clusters boost regional economic performance. However, in the present manuscript a simple model is introduced which suggests the reverse is true regarding employment growth. It is argued that specialised regions are prone to be affected stronger by sector-specific demand shocks than diversified ones and, therefore, show higher variances in employment growth rates. A test on the equality of variances in employment growth rates across two groups of specialised and diversified cities is conducted. It shows that, in Germany, variances are higher in the group of specialised cities. Thus, regional specialisation is more insecure than diversification with regard to stable employment growth rates. --

Efficient quantum memory using a weakly absorbing sample

A light-storage experiment with a total (storage and retrieval) efficiency $\eta=58 \pm 5$ is carried out by enclosing a sample, with a single pass absorption of 10%, in an impedance-matched cavity. The experiment is carried out using the Atomic Frequency Comb (AFC) technique in a praseodymium-doped crystal ($0.05$) and the cavity is created by reflection coating the crystal surfaces. The AFC technique has previously by far demonstrated the highest multi-mode capacity of all quantum memory concepts tested experimentally. We claim that the present work shows that it is realistic to create efficient, on-demand, long storage time AFC memories

Der digitalisierte Forscher

Im 21. Jahrhundert ist der akademische Forscher nicht nur zunehmend digital informiert; die gesetzlich gebotene Evaluierung seiner Forschungsleistungen ist mitunter auch eine digital abgestützte. Dies bedeutet nicht nur Vorteile, sondern auch Risiken für den akademischen Forscher

Using electric fields for pulse compression and group velocity control

In this article, we experimentally demonstrate a new way of controlling the group velocity of an optical pulse by using a combination of spectral hole burning, slow light effect and linear Stark effect in a rare-earth-ion-doped crystal. The group velocity can be changed continuously by a factor of 20 without significant pulse distortion or absorption of the pulse energy. With a similar technique, an optical pulse can also be compressed in time. Theoretical simulations were developed to simulate the group velocity control and the pulse compression processes. The group velocity as well as the pulse reshaping are solely controlled by external voltages which makes it promising in quantum information and quantum communication processes. It is also proposed that the group velocity can be changed even more in an Er doped crystal while at the same time having a transmission band matching the telecommunication wavelength.Comment: 8 pages, 7 figure

Fast all-optical nuclear spin echo technique based on EIT

We demonstrate an all-optical Raman spin echo technique, using Electromagnetically Induced Transparency (EIT) to create the different pulses of the spin echo sequence: initialization, pi-rotation, and readout. The first pulse of the sequence induces coherence directly from a mixed state, and the technique is used to measure the nuclear spin coherence of an inhomogeneously broadened ensemble of rare-earth ions (Pr$^{3+}$). In contrast to previous experiments it does not require any preparatory hole burning pulse sequences, which greatly shortens the total duration of the sequence. The effect of the different pulses is characterized by quantum state tomography and is compared with simulations. We demonstrate two applications of the technique by using the spin echo sequence to accurately compensate a magnetic field across our sample, and to measure the coherence time at high temperatures up to 11 K, where standard preparation techniques are difficult to implement. We explore the potential of the technique and possible applications.Comment: 8 pages, 6 figure