1,626 research outputs found
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
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 () 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 abgestĂĽtzte. Dies bedeutet nicht nur Vorteile, sondern auch Risiken fĂĽr 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). 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
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