QUantum Enhanced Sensing with Trapped IONs (QUESTIONs)

Summary

This project aims to develop a scalable quantum-enhanced trapped-ion sensor that goes beyond the current state of the art. The sensor is based on quantum metrology of entangled states in singly-ionized barium (Ba$^+$) ions: an atomic system that is especially well suited for this novel technique. Besides the electronic ground state, two electronically excited states with a particularly long radiative lifetime (around 30 s and 80 s) will be used to design a variety of entangled sensor states that reject correlated noise. In this manner, the sensor state becomes insensitive to the main source for decoherence induced by fluctuations of the magnetic field environment, and the exceptionally long interrogation time of $>30$ s/ion can be fully exploited (limited only by spontaneous decay). This enables extension to a larger number ions to take advantage of the more favourable stability scaling of correlated quantum systems. Two main applications are explored with the novel quantum sensor: magnetic field gradiometry with a high spatial resolution and robust clock spectroscopy with a stability scaling that improves upon classical atomic clocks.

For the experimental realization Ba$^+$ ions will be trapped in a radiofrequency ion trap. High-fidelity single-qubit gate operation (> 99.9%) will be implemented based on the two narrow clock transitions in Ba$^+$. Techniques will be implemented to realise ground state cooling and single-ion addressing for scalability of the sensor.