Sympathetic cooling of a trapped proton mediated by an LC circuit

Abstract

Efficient cooling of trapped charged particles is essential to many fundamental physics experiments1,2, to high-precision metrology3,4 and to quantum technology5,6. Until now, sympathetic cooling has required close-range Coulomb interactions7,8, but there has been a sustained desire to bring laser-cooling techniques to particles in macroscopically separated traps5,9,10, extending quantum control techniques to previously inaccessible particles such as highly charged ions, molecular ions and antimatter. Here we demonstrate sympathetic cooling of a single proton using laser-cooled Be+ ions in spatially separated Penning traps. The traps are connected by a superconducting LC circuit that enables energy exchange over a distance of 9 cm. We also 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 environmental temperature. Notably, as this technique uses only image–current interactions, it can be easily applied to an experiment with antiprotons1, facilitating improved precision in matter–antimatter comparisons11 and dark matter searches12,13.

Sympathetic cooling schemes for separately trapped ions coupled via image currents

“…In this section, we have shown that our simulations are able to unambiguously reproduce the observed experimental signatures [12]. By giving access to the time domain data, the results provide another layer of understanding.…”

“…Reference [12] employed the coupling scheme with a common RLC resonator. First, the coupling between the proton and 9 Be + ions was demonstrated above the resonator temperature by bringing the proton to resonance with excited beryllium ions.…”

“…In order to realize this boost in precision experimentally, we develop technologies and methods to sympathetically cool the proton with a cloud of laser-cooled 9 Be + stored in a separate trap a few cm away, for which we have recently performed the proof-of-principle measurement [12]. The coupling is achieved through image currents induced in a common electrode or a common resonator.…”

“…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. The experimental configurations are depicted schematically in figure 2 and described in more detail in references [2,12,42].…”

“…Here, the charged particle species are coupled through image currents induced in adjacent trap electrodes, allowing a macroscopic separation of the target species and cooling species. Recently, our group has published the first experimental results on sympathetically cooling a single proton in a Penning trap by coupling it to a cloud of laser-cooled 9 Be + ions located in a separate trap [12]. In this experiment, the coupling between the ions was mediated by a common superconducting RLC resonator, which is usually used for particle detection [13].…”