Spin dynamics as a source of entangled atoms
At ultra low temperatures neutral atoms can form a Bose-Einstein Condensates (BEC) - the atomic analougue of the laser in optics. Such condensates offer a high degree of control and can be used to realize sensors with highest precision and to investigat fundamental effects. In a so-called dipole trap, which can be realized by a red detuned laser beam, atoms in all spin states can be captured. Thereby, the BEC gains an additional degree of freedom and a so-called spinor condensate can be created.
Within this project, we were able to demonstrate that spin changing collisions in a spinor condensate can be employed for the creation of entanglement in close analogy to parametric down conversion in optics. We could demonstrate the first creation of continuous variable Einstein-Podolsky-Rosen entanglement and new interferometry concepts which overcome the classical precision limit of atomic sensors.
Parametric amplification of matter waves
Optical parametric amplification is a well-established method for the creation of entangled photons and squeezed states of light. In this project we demonstrated that spin changing collisions in a spinor condensate can act as a parametric amplifier for atoms.
In optical parametric down conversion a strong pump laser beam enters a non-linear crystal. This non-linearity leads to the conversion of a pump to photon to two photons at half the frequency. Thereby the so-called signal and idler beams build up, which exhibit entanglement and can be used to create squeezed states of light.
The parametric amplification of atoms starts with the preparation of a BEC in Zeeman level mF=0 which acts as the coherent pump. If a resonance condition is fulfilled, two atoms in this condensate can collide and thereby one atom is transferred to the level mF=-1 while the other atom is transferred to the level mF=+1 conserving the projection of the total spin. This pair creation process is intrinsically non-linear and leads to the creation of entangled states in the Zeeman level mF=-1 and mF=+1. These levels are the analogue of the signal and idler beam in optics.
Within the procjet a number of new experimental techniques were implemented and investigated. More details on the experimental apparatus can befound within the section Experiment.
Recent experimental investigations performed within the project:
Research on spinor gases:
- Continuous-variable Einstein-Podolsky-Rosen entanglement
- Interaction-free measurements via quantum Zeno stabilization
- Creation of multi-particle entangled Dicke states
- Twin-matter waves for interferometry beyond the SQL
- Symmetry breaking in spinor condensates
- Multi-resonant spinor dynamic
- Parametric amplification of vacuum fluctuations
Research on Potassium-Rubidium mixtures:
- Observation of 40K 87Rb Feshbach Resonances
- Radio frequency association of heteronuclear Feshbach molecules
Research on experimental techniques:
- Light-induced atom desorption (LIAD) for large rubidium and potassium ensembles
- Transport of a quantum degenerate heteronuclear mixture