Parametric amplification of quantum fluctuations constitutes a fundamental mechanism for spontaneous symmetry breaking. In our experiments, a spinor condensate acts as a parametric amplifier of spin ...modes, resulting in a twofold spontaneous breaking of spatial and spin symmetry in the amplified clouds. Our experiments permit a precise analysis of the amplification in specific spatial Bessel-like modes, allowing for the detailed understanding of the double symmetry breaking. On resonances that create vortex-antivortex superpositions, we show that the cylindrical spatial symmetry is spontaneously broken, but phase squeezing prevents spin-symmetry breaking. If, however, nondegenerate spin modes contribute to the amplification, quantum interferences lead to spin-dependent density profiles and hence spontaneously formed patterns in the longitudinal magnetization.
We analyze the spinor dynamics of a 87Rb F=2 condensate initially prepared in the m(F) = 0 Zeeman sublevel. We show that this dynamics, characterized by the creation of correlated atomic pairs in ...m(F) = +/-1, presents an intriguing multiresonant magnetic-field dependence induced by the trap inhomogeneity. This dependence is directly linked to the most unstable Bogoliubov spin excitations of the initial m(F) = 0 condensate, showing that, in general, even a qualitative understanding of the pair-creation efficiency in a spinor condensate requires a careful consideration of the confinement.
The occurrence of phase fluctuations due to thermal excitations in Bose-Einstein condensates (BECs) is studied for a variety of temperatures and trap geometries. We observe the statistical nature of ...the appearance of phase fluctuations and characterize the dependence of their average value on temperature, number of particles, and the trapping potential. We find pronounced phase fluctuations for condensates in very elongated traps in a broad temperature range. The results are of great importance for the realization of BEC in quasi-1D geometries, for matter wave interferometry with BECs, as well as for coherence properties of guided atom laser beams.
We present a compact and transportable inertial sensor for precision sensing of rotations and accelerations. The sensor consists of a dual atom interferometer operated with laser-cooled
87
Rb. Raman ...processes are employed to coherently manipulate the matter waves. We describe and characterize the experimental apparatus. A method for passing from a compact geometry to an extended interferometer with three independent atom-light interaction zones is proposed and investigated. The extended geometry will enhance the sensitivity by more than two orders of magnitude which is necessary to achieve sensitivities better than 10
-8
rad/s/
.
We measure the intensity correlation function of two interfering spatially displaced copies of phase fluctuating Bose-Einstein condensates. It is shown that this corresponds to a measurement of the ...phase correlation properties of the initial condensate. Analogous to the method used in the stellar interferometer experiment of Hanbury Brown and Twiss, we use spatial intensity correlations to determine the phase coherence lengths of elongated condensates. We find good agreement with our prediction of the correlation function and confirm the expected coherence length.
We experimentally demonstrate novel structures for the realization of registers of atomic qubits: We trap neutral atoms in one- and two-dimensional arrays of far-detuned dipole traps obtained by ...focusing a red-detuned laser beam with a microfabricated array of microlenses. We are able to selectively address individual trap sites due to their large lateral separation of 125 microm. We initialize and read out different internal states for the individual sites. We also create two interleaved sets of trap arrays with adjustable separation, as required for many proposed implementations of quantum gate operations.
We report the first implementation of a Gauss sum factorization algorithm by an internal state Ramsey interferometer using cold atoms. A sequence of appropriately designed light pulses interacts with ...an ensemble of cold rubidium atoms. The final population in the involved atomic levels determines a Gauss sum. With this technique we factor the number N=263193.
Recently, laser systems have become available which generate ultrashort laser pulses with a duration of 100-200 femtoseconds (fs). By generating micro-plasmas inside the corneal stroma with fs ...pulses, it is possible to achieve a cutting effect inside the tissue while leaving the anterior layers intact. The energy threshold to generate a micro-plasma with fs pulses is some orders of magnitude lower than it is for picosecond or nanosecond pulses. This results in a strong reduction of the thermal and mechanical damage of the surrounding tissue.
With a titanium:sapphire fs laser system, the cutting effect on corneal tissue from freshly enucleated porcine eye globes was investigated with different pulse energies. The irradiated samples were examined by light and electron microscopy. The laser-induced pressure transients and the laser-induced bubble formation were analysed with a broadband acoustic transducer and by flash photography.
With fs laser pulses, the extent of thermal and mechanical damage of the adjacent tissue is in the order of 1 microm or below and therefore comparable with the tissue alterations after ArF excimer laser ablation. Using pulse energies of approximately 1-2 microJ and a spot diameter of 5-10 microm, intrastromal cuts can be performed very precisely in order to prepare corneal flaps and lenticules.
Femtosecond photodisruption has the potential to become an attractive tool for intrastromal refractive surgery.
PDF
