LC circuit mediated sympathetic cooling of a proton via image currents

Abstract

Efficient cooling of trapped charged particles is essential in many fundamental physics experiments, for high-precision metrology, and for quantum technology. Until now, ion-ion coupling for sympathetic cooling or quantum state control has been limited to ion species with accessible optical transitions or has required close-range Coulomb interactions. To overcome this limitation and further develop scalable quantum control techniques, there has been a sustained desire to extend laser-cooling techniques to particles in macroscopically separated traps, opening quantum control techniques to previously inaccessible particles such as highly charged ions, molecular ions, and antimatter particles. Here, we demonstrate sympathetic cooling of a single proton by laser cooled Be+ ions stored in a spatially separated Penning trap. The two traps are connected by a superconducting LC circuit that enables energy exchange over a distance of 9 cm. We simultaneously demonstrate the cooling of a resonant mode of a macroscopic LC circuit with laser-cooled ions and sympathetic cooling of an individually trapped proton, reaching temperatures far below the environment temperature. Importantly, as this technique does not rely on the direct Coulomb interaction but rather on image-current interactions, it can be easily applied to an experiment with antiprotons, facilitating improved precision in matter-antimatter comparisons and dark matter searches.

Sympathetic cooling schemes for separately trapped ions coupled via image currents

“…One technique which satisfies the challenging requirements described in sections 1 and 2.2 is image-current coupling, where the proton is sympathetically cooled by a cloud of laser-cooled 9 Be + stored in a separate trap and the particles are coupled through image currents. A trap stack consisting of five traps was developed for our experiment, of which four are used to implement the coupling schemes and one is used for spin state analysis [12,40,41]. From an instrumentation point of view, our apparatus allows two different types of image-current couplings, namely coupling via a common endcap electrode or coupling via a common RLC resonator.…”