entanglement enhanced Trapped Atomc Clock on a Chip – ee-TACC

Typically, the performance of measurement devices is limited by deleterious effects such as thermal noise and vibration. Notable exceptions are atomic clocks, which benefit from the exquisitely stable properties of atoms and operate very near their fundamental limits. Driving devices to their physical limits will open new application spaces for civilian and defence activity. Indeed, many everyday applications already require exceptionally precise time and frequency standards enabled only by atomic clocks. The Global Positioning System (GPS), inertial navigation and telecommunication are key examples.
Thanks to (laboratory-size) atomic clocks, the second is the best realised SI unit and stunning tests of fundamental science are performed. In parallel to the search for ever higher precision, development goes towards small portable devices for mobile, in-the-field applications. Here, chip-scale atomic clocks (CSAC) present incredibly small size (~ 1 ccm), but reach only moderate clock performance. Compact (litre-size) microwave clocks under development demonstrate stability down to 10^-13 at 1s rivalling the traditional hydrogen-maser, but in a portable and much cheaper physics package. These are ideally suited for many civilian and defence applications, on earth and in space. Here, research can help to deploy their enormous potential and assure independence from foreign supply.

For a given atomic transition, the most efficient way of improving the clock stability is to increase the interrogation time. This is the reason for the revolutionising success of laser-cooling in metrology and has led to the construction of atomic fountain clocks and atom gravimeters. In these, the time of free fall is ~0.5 s. With the Trapped Atom Clock on a Chip (TACC), our LKB/SYRTE consortium has chosen a radically new approach, the interrogation of trapped atoms. In a first generation TACC we have validated the new concept through the discovery of interrogation times of up to 58s - a world first for neutral atoms. The current set-up reaches a very competitive clock stability of 5.8 10^-13 at 1s and 6 10^-15 at 30 000 s.

In the here proposed new explorative study, we target a step-wise improvement of the TACC clock stability. We will conduct two explorative studies on quantum non-destructive detection and quantum engineered spin squeezing, which, each for the first time test innovative fundamental physics approaches in a true metrology grade instrument. In doing so we will push the stability of a 2nd generation set-up to 10^-13\tau^-1/2, possibly even into the 10^-14 range. We will furthermore adapt the atomic interrogation cycle allowing the use of quartz local oscillators smaller and cheaper than alternative oscillators. The expected result will put TACC in a leading position among all compact clocks and even rival the stability of the best atomic fountain clocks.

TACC applies the innovative technique of atom chips, where atom cooling, trapping and interrogation are realised on a microchip. Utilising the power of micro-fabrication, this technique presents enormous potential for embarked systems and multi-sensor integration. Here we propose to go one step further in including miniature optical elements on the chip, which is an important step towards miniaturisation of cold atom experiments.

The expected fundamental physics results will address outstanding challenges in physics and will be broadly applicable across disciplines. They will constitute a far reaching example for a vast range of metrology instruments (clocks, magnetometers, inertial sensors) opening the way to a new generation of highest performance devices. Furthermore, the quantum engineering tools we propose to develop may find application in closely related fields like quantum computing.