Michael Erhard

Dynamics of F = 2 Spinor Bose-Einstein Condensates

We experimentally investigate and analyze the rich dynamics in F=2 spinor Bose-Einstein condensates of 87Rb. An interplay between mean-field driven spin dynamics and hyperfine-changing losses in addition to interactions with the thermal component is observed. In particular, we measure conversion rates in the range of 10(-12) cm(3) s(-1) for spin-changing collisions within the F=2 manifold and spin-dependent loss rates in the range of 10(-13) cm(3) s(-1) for hyperfine-changing collisions. We observe polar behavior in the F=2 ground state of 87Rb, while we find the F=1 ground state to be ferromagnetic. We further see a magnetization for condensates prepared with nonzero total spin.

Control of Towing Kites for Seagoing Vessels

In this paper, we present the basic features of the flight control of the SkySails towing kite system. After introducing the coordinate definitions and the basic system dynamics, we introduce a novel model used for controller design and justify its main dynamics with results from system identification based on numerous sea trials. We then present the controller design, which we successfully use for operational flights for several years. Finally, we explain the generation of dynamical flight patterns.

Measurement of a mixed-spin-channel Feshbach resonance in {sup 87}Rb

We report on the observation of a mixed-spin-channel Feshbach resonance at the low magnetic field value of 9.09{+-}0.01 G for a mixture of |2,-1> and |1,+1> states in {sup 87}Rb. This mixture is important for applications of multicomponent Bose-Einstein condensates of {sup 87}Rb, e.g., in spin mixture physics and for quantum entanglement. Values for position, height, and width of the resonance are reported and compared to a recent theoretical calculation of this resonance.

Theory and Experimental Validation of a Simple Comprehensible Model of Tethered Kite Dynamics Used for Controller Design

We present a simple model for the dynamics and aerodynamics of a tethered kite system and validate it by experimental flight data. After introduction of system setup and model assumptions, the equations of motion for the kinematics are derived and discussed. Then the turn rate law for the kite response to a steering deflection is introduced. The tutorial introduction of the model is finalized by an extension for varying tether lengths, which is the regular operation mode of certain classes of airborne wind energy setups. The second part starts with a summary of the sensor setup. Then, the turn rate law, as distinguishing feature of the model, is illustrated and validated by experimental data. Subsequently, we discuss the kinematics of the kite by comparing model based prediction to experiment. Conclusively, we briefly summarize controller design considerations and discuss the flight controller performance, which further proves the validity of the model as it is based on a feed forward term which in turn, is build on the presented model.

Bose-Einstein condensation at constant temperature

We present an experimental approach to Bose-Einstein condensation by increasing the particle number of the system at almost constant temperature. In particular, the emergence of a new condensate is observed in multicomponent

Dynamics and thermodynamics in spinor quantum gases

F=1

A quaternion-based model for optimal control of the SkySails airborne wind energy system

spinor condensates of

A quaternion‐based model for optimal control of an airborne wind energy system

^{87}\mathrm{Rb}

Software System Architecture for Control of Tethered Kites

. Furthermore, we develop a simple rate-equation model for multicomponent Bose-Einstein condensate thermodynamics at finite temperature which well reproduces the measured effects.

Warping NMPC for Online Generation and Tracking of Optimal Trajectories

We discuss magnetism in spinor quantum gases theoretically and experimentally with emphasis on temporal dynamics of the spinor order parameter in the presence of an external magnetic field. In a simple coupled Gross–Pitaevskii picture we observe a dramatic suppression of spin dynamics due to quadratic Zeeman “dephasing”. In view of an inhomogeneous density profile of the trapped condensate we present evidence of spatial variations of spin dynamics. In addition we study spinor quantum gases as a model system for thermodynamics of Bose–Einstein condensation. As a particular example we present measurements on condensate magnetisation due to the interaction with a thermal bath.