TACC - Trapped Atom Clock on a Chip

In parallel to the search for ever higher acurray of atomic clocks and interferometers, development goes towards small portable devices for mobile, in-the-field applications including satelite navigation (GPS, GALILEO), inertial navigation and telecommunication.

For a given atomic transition, the most efficient way of improving the clock stability is increasing the interrogation time. This is the reason for the revolutionising success of laser cooling, which slows atoms to cm/s. At so low speed, gravity become dominant limiting the interrogation time to 0.5 s for a 1 m tall set-up. With the “Trapped Atom Clock on a Chip (TACC)”, we have chosen a complementary approach in interrogating trapped atoms. Magnetic levitation compensates gravity and the residual thermal expansion. This enables several seconds observation time in a cm-scale set-up. In addition, the trap allows cooling the atoms to nanoKelvin temperatures and produce, at will, ultra-cold gases or Bose Einstein condensates.

Absorption images of the phase transition to BEC.

The low temperature and trap geometry have proven full of rich physics, since the confinement enhances atom-atom interactions by 4 orders of magnitude. Near the onset of BEC, we have discovered a new spin synchronisation mechanism based on the quantum nature of the interactions [Deutsch et al PRL 105, 020401 (2010)]. Bose statistics open an energy gap between the symmetric and anti-symmetric two-body wavefunctions [Maineult et al PRL 109, 020407 (2012)]. The gap hinders dephasing and thereby sustains extraordinarily long coherences times of 5812 s.

TACC applies the innovative technique of atom chips, where atom cooling, trapping and interrogation are realised on a microchip. Lithographically structured gold wires carry DC currents for magnetic levitation as well as RF and microwave signals for atom cooling and interrogation. Utilising the power and low cost of micro-fabrication, this technique presents enormous potential for the realisation of embarked systems. In a 1st generation set-up, we have demonstrated a competitive clock stability of 5.8 10^-13 at 1s [Szmuk et al arXiv:1502.03864].

Currently we are constructing a 2nd generation set-up to further improve the clock stability through quantum engineered spin squeezing. Spin squeezing is a form of entanglement in the atomic ensemble that redistributes fundamental quantum uncertainty away from the atomic phase, thus overcoming the standard quantum limit imposed by the quantum projection noise. Central tool is the installation of an optical fibre cavity on the atom chip [Hunger et al New Journal of Physics 12, 065038 (2010)]. Including miniature optical elements on the chip is an important step towards miniaturisation of atomic clocks and atom sensors.

The project is conducted in collaboration with the group of J. Reichel at the Laboratoire Kastler Brossel at the Ecole Normale Supérieure. We have theory collaborations with J.-N. Fuchs at the Laboratoire de physique théorique de la matière condensée, F. Piechon at the Laboratoire de physique des solides and K. Gibble at the Pennsylvania State University.

The project has received funding from ANR, CNES, DGA, EURAMET, FIRST-TF, LNE, Observatoire de Paris, and PSL.

Contact: Carlos Garrido Alzar