Microwave Frequencies Metrology

TACC - Trapped Atom Clock on a Chip

Since the discovery of laser cooling and Bose-Einstein condensation in diluted gases, many experiments in atomic physics and metrology seek to continuously improve the control over the atoms' external and internal states. Magnetic and electric fields slow-down the atoms' movement and stock them in microscopic traps. Radiofrequency, micro-wave and light signals prepare and interrogate the electronic state of the atoms. The experiment "TACC - Trapped Atom Clock on a Chip" aims at creating all fields for the control and interrogation on a chip of a few cm². A micro-wave signal interrogates the clock transition while the atoms are magnetically trapped. The trap compensates gravity and the expansion due to the residual temperature, thereby allowing observation times of one second or more. The "TACC" can be operated using thermal atoms as well as a Bose-Einstein condensate and seeks to establish a comparison between these two fundamentally different regimes. The atoms having a sub-micro Kelvin temperature, are kept between a few microns and one millimetre above the surface, which herself stays at room temperature. Effects due to this important temperature gradient as well as other interactions between the atoms and the surface will be investigated. Small modifications to the clock technology allow the realisation of an integrated atom interferometer or a microscope probing even weak interactions.

Left: Photo of a double layer chip glued onto the glass vacuum cell. The base chip closes the vacuum and thereby stays accessible for electric connection and cooling. The dimensions of the glass cube are 35 x 35 x 42 mm³.
Right: Schematic of the clock operation. Current carrying wires on the chip create the magnetic fields to trap a cloud of ultra-cold atoms above the surface. The central wire carries the microwave signal interrogating the clock transition.