Carmelo Mordini

Single-atom quantum sensors offer high spatial resolution and high sensitivity to electric and magnetic fields. Among them, trapped ions offer exceptional performance in sensing electric fields, which has been used in particular to probe these in the proximity of metallic surfaces. However, the flexibility of previous work was limited by the use of radio-frequency trapping fields, which has restricted spatial scanning to linear translations, and calls into question whether observed phenomena are connected to the presence of the radio-frequency fields. Here, using a Penning trap instead, we demonstrate a single ion probe which offers three-dimensional position scanning at distances between $50$ $μ\mathrm{m}$ and $450$ $μ\mathrm{m}$ from a metallic surface and above a $200\times200$ $μ\mathrm{m}^{2}$ area, allowing us to reconstruct static and time-varying electric as well as magnetic fields. We use this to map charge distributions on the metallic surface and noise stemming from it. The methods demonstrated here allow similar probing to be carried out on samples with a variety of materials, surface constitutions and geometries, providing a new tool for surface science.

In this work we study the interaction of trapped ions with a state-dependent, high-intensity optical lattice formed above an ion trap chip using integrated photonics. We use a single ion to map the optical potential landscape over many periods of the standing-wave field. For a single ion sitting in the centre of the lattice we observe a state-dependent trap-frequency shift of $2π\times 3.33(4)$ kHz, corresponding to a bare optical potential of $2π\times 76.8(5)$ kHz for the electronic ground state. We extend this to two ions, measuring state-dependent shifts of both axial modes. Additionally, using the internal-state dependence of the interaction, we perform a direct measurement of the energy distribution of the motion of a single ion using carrier spectroscopy. Improvements to the setup would allow to increase the state-dependent curvature by more than 50 times, providing a tool which can be utilised for motional state control, and multi-ion gates using optical potentials produced in a scalable fashion.

Multiplexed operations and extended coherent control over multiple trapping sites are fundamental requirements for a trapped-ion processor in a large scale architecture. Here we demonstrate these building blocks using a surface-electrode trap with integrated photonic components which are scalable to larger numbers of zones. We implement a Ramsey sequence using the integrated light in two zones, separated by 375 $μ$m, performing transport of the ion from one zone to the other in 200 $μ$s between pulses. In order to achieve low motional excitation during transport, we developed techniques to measure and mitigate the effect of the exposed dielectric surfaces used to deliver the integrated light to the ion. We also demonstrate simultaneous control of two ions in separate zones with low optical crosstalk, and use this to perform simultaneous spectroscopy to correlate field noise between the two sites. Our work demonstrates the first transport and coherent multi-zone operations in integrated photonic ion trap systems, forming the basis for further scaling in the trapped-ion QCCD architecture.

Using a single calcium ion confined in a surface-electrode trap, we study the interaction of electric quadrupole transitions with a passively phase-stable optical standing wave field sourced by photonics integrated within the trap. We characterize the optical fields through spatial mapping of the Rabi frequencies of both carrier and motional sideband transitions as well as AC Stark shifts. Our measurements demonstrate the ability to engineer favorable combinations of sideband and carrier Rabi frequency as well as AC Stark shifts for specific tasks in quantum state control and metrology.