> Zum Inhalt


Head of the group: Prof. Dr. Thorsten SchummTel.: +43-1-58801-141896Fax: +43-1-58801-14199 Room number: ZA 01 40

TU Wien - Atominstitut
Stadionallee 2
1020 Vienna

Caesium Interferometer

Almost a hundred years after being postulated and observed, the wave properties of massive particles serve as testbed for modern quantum physics.

The matter wave properties of particles can be easily studied in interferometers, where two spatially separated waves are brought to overlap and form the characteristic interference pattern. Interference of matter waves has been observed for electrons, neutrons, atoms and even large molecules.

With the new Caesium setup, we want to make use of matter waves for metrology. We exploit all properties a gas of alkali atoms has to offer: Caesium atoms can be laser-cooled and trapped with magnetic fields and laser beams. After additional evaporative cooling, one achieves a Bose Einstein condensate (BEC). In a BEC all atoms find themselves in the exact same quantum state and can be described by a single macroscopic wave function.

1: Illustration of Bose-Einstein condensates in double well potential

We realize an interferometer by continuously deforming the single potential well, in which the BEC is trapped, into a double well potential. The splitting of the condensate wave function while controlling the relative phase is the first step of the interferometer sequence.  Since this step will be repeated for the measurements hundreds of times, the relative phase needs to be highly reproducible to serve as reference.

The condensates accumulate a phase difference dependent on their energy difference during the time span in which they are fully separated. The difference in energy in turn depends on the atomic interactions and inhomogeneities of ambient fields. A tilt of the double well with respect to the gravitational acceleration g results a small difference in potential energy, which can be detected in the interference pattern.

To observe such small effects, our Caesium interferometer needs an exceptionally high sensitivity, which we want to achieve by a long phase accumulation time. In order to avoid the typical interaction driven phase diffusion, we want to control and minimize the interaction strength by external fields. Shielding against external influences on the experimental setup will be essential.

2: Illustration of our atomchip with optical dipole trap

A compact experiment will help us to achieve the appropriate control: The setup is based on a ColdQuanta RuBECi system with a double-chamber glass cell, where the Caesium atoms can be trapped and cooled in a magneto optic trap (MOT). Magnetic fields are generated by permanent magnets, coils and current carrying wires on a so-called atomchip. Optical traps, realized by focused laser beams, can be brought in close vicinity of the atom chip, to prepare the atoms for the interferometer sequence.

The experiment is currently set up in the lab – we will keep you posted on the progress on this page.