Logo Leibniz Universität Hannover
Research Training Group 1729/Leibniz Universität Hannover
Logo Leibniz Universität Hannover
Research Training Group 1729/Leibniz Universität Hannover
  • Zielgruppen
  • Suche
 

Seminar 11.04.13; 10:15 h; Room D 326

Dominika Fim
Institute of Quantum Optics
Leibniz Universität Hannover

Optical lattice clocks

Atomic clocks are characterized in terms of accuracy and their stability. The latter can be improved by choosing a higher frequency for interrogation. State-of-the-art optical lattice clocks use interrogation transitions in the optical domain and therefore already have outperformed the best microwave clocks in terms of stability, which are used for time-keeping. Besides the stability for operating a clock a well known transition frequency is important. Magnesium is a suitable candidate for operating an optical lattice clock. The spin forbidden 1S03P0 transition allows spectroscopy in the optical regime with sub-Hertz linewidth. Additionally, Magnesium offers a relative simple electronic structure this is leading to good calculable uncertainties of shifts, for example due to the black body radiation (BBR). In my talk I will present the general principal of optical lattice clocks and will later on focus in detail on a magnesium based frequency standard.

 

Seminar 13.06.2013, 14:00 h, Room D326

Falk Wächtler
Institute of Theoretical Physics
Leibniz Universität Hannover

Dipolar Bose gases in random potentials

Abstract: The effects of impurities in a given system are under intense investigation since more than 50 years. Experimental and theoretical studies showed that depending on the interaction and disorder strength different quantum phases exist in such systems. We theoretically describe quasi one- and two-dimensional systems with an underlying random potential in a mean-field description and investigate the influence of the dipole-dipole interaction and its long-range character. We show how the crossover boundaries between the quantum phases change due to the dipole-dipole interaction and describe Blockade effects in different dimensions. Furthermore we studied the ground state properties of dipolar Bose gases for weak disorder and found beside the screening effect of the kinetic energy an additional effect originating from the dipole-dipole interaction.

 

Seminar 27.06.2013, 10:15 h, Room D326

Sebastian Häfner
Physikalisch-Technische Bundesanstalt

Ultra stable Laser(s) for Sr optical lattice clock(s)

The stability of current optical clocks is limited through the short term interrogation laser. This talk is focused on reference cavities for the clock laser systems for a stationary and a transportable Sr lattice clock. The mechanical length stability of the cavities provide the frequency stability of the clock lasers. The stability of the length of a well designed and operated cavity is limited by the Brownian motion of the materials, especially of the mirrors. This influence can be reduced by using longer cavities at the cost of a higher sensitivity to vibrations. This concept of longer cavities is used to build up a 48 cm long ULE glas cavity, which provides the short term stability for our stationary Sr lattice clock. In the talk the required steps for the realization of this cavity will be described and preliminary results of the laser instability down to 1.5·10-16 are presented, as well as preliminary instabilities of the stationary Sr lattice clock at the PTB. Further a  transportable 12cm long ULE glas cavity system which can withstand up to 50 g of acceleration will be presented. A transportable clock laser system which was locked to this cavity showed a frequency instability of 5·10-16 at 10s. This clock laser system is part of the transportable Sr lattice clock, which is currently set up at the PTB.

 

Seminar 04.07.2013, 10:15 h, Room D326

Jan Peise
Institute of Quantum Optics
Leibniz Universität Hannover

Entanglement in a Bose-Einstein condensate

In a wide range of modern quantum mechanics, the generation of entanglement plays an important role. As a prominent example entanglement is needed to surpass the shot noise limit in interferometry. For this purpose it is important to generate entangled states with a large number of atoms. The creation of such states as well as the proof of entanglement is experimentally challenging.

We show how such states are generated by means of spin dynamics in a Bose-Einstein condensate. This mechanism is investigated for the two hyperfine states of

Seminar 11.07.2013, 10:15 h, Room D326

Stefan Vogt
Physikalisch-Technische Bundesanstalt, Braunschweig

Building a Transportable Strontium Lattice Clock

Optical clocks have reached a level of stability and accuracy beyond the performance of the primary Cesium clocks that are realizing the SI second.  At an accuracy level of 10-17 new applications come into view. These are for example relativistic geodesy or tests of fundamental physics. To perform these tests and to evaluate optical clocks at the highest performance it is necessary to measure frequency ratios between different types of optical clocks directly. One difficulty for this kind of comparison is that modern optical clocks are bulky setups which are not easily transportable while remote comparisons require dedicated optical-fiber links that are still under development.

I want to present the latest progress on a new lattice clock setup operating with neutral strontium atoms. This setup is designed to be transportable to be brought to other laboratories and be compared to the local optical clocks. The design goal is to reach a level of inaccuracy below 10 -17 limited by the influence of blackbody radiation emitted from the vacuum chamber at room temperature.