At the interface of quantum physics and precision metrology, quantum metrology is an emerging field of research which investigates the use of quantum-mechanical states and mechanisms to further improve the performance of precision measurement devices. For example, the use of a special form of entanglement called “spin squeezing” should make it possible to reduce the measurement noise in atomic clocks and atom interferometers beyond the fundamental classical minimum which currently limits their stability.

The Trapped-Atom Clock on a Chip (TACC) is a project performed in collaboration by the Ecole Normale Superieure (ENS) and the Observatoire de Paris - SYRTE. It uses atom chip technology to realize a portable, very compact atomic clock with trapped atoms. Recent experiments with this clock have led us to discover a quantum mechanism, spin self- rephasing, which naturally occurs in the ensemble of trapped atoms and improves the coherence time of the clock transition by more than a factor of 10. Using this new mechanism, the clock’s short-term stability is now better than the best atomic clocks that are commercially available, and there is still a lot of potential for further improvement. Thus, it has become one of the first examples of quantum metrology actually applied to a state-of-the-art precision measurement device.

The proposed PhD project aims at further exploiting quantum metrology in trapped atom clocks. A better understanding of the spin self-rephasing effect will be obtained by experimentally and theoretically studying its relation to entanglement between the atomic spins. Furthermore, spin squeezing will be implemented on TACC to reduce the measurement noise beyond its classical limit. This will potentially improve the clock performance by more than an order of magnitude and is likely to be re-used in other types of precision measurement.

ENS and SYRTE are pioneers of laser cooling, quantum effects in atomic systems, and cold atom atomic clocks. SYRTE operates some of the best atomic clocks in the world. The collaboration of the two laboratories thus creates a most favourable environment for the study of quantum metrology in “real-life” situations that are really relevant to applications. A PhD scholarship is open for this project financed by the French space agency CNES.