W. Quint

We demonstrate efficient sub-thermal cooling of the modified cyclotron mode of a single trapped antiproton and reach particle temperatures $T_+=E_+/k_\text{B}$ below $200\,$mK in preparation times shorter than $500\,$s. This corresponds to the fastest resistive single-particle cyclotron cooling to sub-thermal temperatures ever demonstrated. By cooling trapped particles to such low energies, we demonstrate the detection of antiproton spin transitions with an error-rate $<0.000025$, more than three orders of magnitude better than in previous best experiments. This method will have enormous impact on multi-Penning-trap experiments that measure magnetic moments with single nuclear spins for tests of matter/antimatter symmetry, high-precision mass-spectrometry, and measurements of electron $g$-factors bound to highly-charged ions that test quantum electrodynamics.

We have built and operated a cryogenic Penning trap arrangement that allows for the efficient production, selection, and long-term storage of highly charged atomic ions. In close similarity to an electron-beam ion trap (EBIT) it works by electron-impact ionisation of atoms inside a dedicated confinement region. The electrons are produced by field emission at liquid-helium temperature and are subsequently accelerated to the keV energy range. The electron beam is reflected through the trap multiple times to increase the ionisation efficiency. We show a characterisation of the system and measurements with argon and tungsten ions up to Ar$^{16+}$ and W$^{27+}$, respectively.

Currently, the only worldwide source of low-energy antiprotons is the AD/ELENA facility located at CERN. To date, all precision measurements on single antiprotons have been conducted at this facility and provide stringent tests of the fundamental interactions and their symmetries. However, the magnetic field fluctuations from the facility operation limit the precision of upcoming measurements. To overcome this limitation, we have designed the transportable antiproton trap system BASE-STEP to relocate antiprotons to laboratories with a calm magnetic environment. We anticipate that the transportable antiproton trap will facilitate enhanced tests of CPT invariance with antiprotons, and provide new experimental possibilities of using transported antiprotons and other accelerator-produced exotic ions. We present here the technical design of the transportable trap system. This includes the transportable superconducting magnet, the cryogenic inlay consisting of the trap stack and the detection systems, and the differential pumping section to suppress the residual gas flow into the cryogenic trap chamber.

Cooling of particles to mK-temperatures is essential for a variety of experiments with trapped charged particles. However, many species of interest lack suitable electronic transitions for direct laser cooling. We study theoretically the remote sympathetic cooling of a single proton with laser-cooled $^9$Be$^+$ in a double-Penning-trap system. We investigate three different cooling schemes and find, based on analytical calculations and numerical simulations, that two of them are capable of achieving proton temperatures of about 10 mK with cooling times on the order of 10 s. In contrast, established methods such as feedback-enhanced resistive cooling with image-current detectors are limited to about 1 K in 100 s. Since the studied techniques are applicable to any trapped charged particle and allow spatial separation between the target ion and the cooling species, they enable a variety of precision measurements based on trapped charged particles to be performed at improved sampling rates and with reduced systematic uncertainties.

Efficient cooling of trapped charged particles is essential to many fundamental physics experiments, to high-precision metrology, and to quantum technology. Until now, sympathetic cooling has required close-range Coulomb interactions, but there has been a sustained desire to bring laser-cooling techniques to particles in macroscopically separated traps, 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 antiprotons, facilitating improved precision in matter-antimatter comparisons and dark matter searches.

We report on the first detailed study of motional heating in a cryogenic Penning trap using a single antiproton. Employing the continuous Stern-Gerlach effect we observe cyclotron quantum transition rates of 6(1) quanta/h and an electric field noise spectral density below $7.5(3.4)\times 10^{-20}\,\text{V}^{2}\text{m}^{-2} \text{Hz}^{-1}$, which corresponds to a scaled noise spectral density below $8.8(4.0)\times 10^{-12}\,\text{V}^{2}\text{m}^{-2}$, results which are more than two orders of magnitude smaller than those reported by other ion trap experiments.

We have performed a detailed experimental study of resistive cooling of large ensembles of highly charged ions such as Ar$^{13+}$ in a cryogenic Penning trap. Different from the measurements reported in [M. Vogel et al., Phys. Rev. A, 043412 (2014)], we observe purely exponential cooling behavior when conditions are chosen to allow collisional thermalization of the ions. We provide evidence that in this situation, resistive cooling time constants and final temperatures are independent of the initial ion energy, and that the cooling time constant of a thermalized ion ensemble is identical to the single-ion cooling time constant. For sufficiently high ion number densities, our measurements show discontinuities in the spectra of motional resonances which indicate a transition of the ion ensemble to a fluid-like state when cooled to temperatures below approximately 14 K. With the final ion temperature presently being 7.5 K, ions of the highest charge states are expected to form ion crystals by mere resistive cooling, in particular not requiring the use of laser cooling.

We present an experiment to sympathetically cool protons and antiprotons in a Penning trap by resonantly coupling the particles to laser cooled beryllium ions using a common endcap technique. Our analysis shows that preparation of (anti)protons at mK temperatures on timescales of tens of seconds is feasible. Successful implementation of the technique will have immediate and significant impact on high-precision comparisons of the fundamental properties of protons and antiprotons. This in turn will provide some of the most stringent tests of the fundamental symmetries of the Standard Model.

We present measurements of resistive and sympathetic cooling of ion clouds confined in a Penning trap. For resistive cooling of a cloud consisting of one ion species, we observe a significant deviation from exponential cooling behavior which is explained by an energy-transfer model. The observed sympathetic cooling of simultaneously confined ion species shows a quadratic dependence on the ion charge state and is hence in agreement with expectations from the physics of dilute non-neutral plasmas.

We present an experimental concept and setup for laser-microwave double-resonance spectroscopy of highly charged ions in a Penning trap. Such spectroscopy allows a highly precise measurement of the Zeeman splittings of fine- and hyperfine-structure levels due the magnetic field of the trap. We have performed detailed calculations of the Zeeman effect in the framework of quantum electrodynamics of bound states as present in such highly charged ions. We find that apart from the linear Zeeman effect, second- and third-order Zeeman effects also contribute to the splittings on a level of 10^-4 and 10^-8, respectively, and hence are accessible to a determination within the achievable spectroscopic resolution of the ARTEMIS experiment currently in preparation.

An overview and status report of the new trapping facility for highly charged ions at the Gesellschaft fuer Schwerionenforschung is presented. The construction of this facility started in 2005 and is expected to be completed in 2008. Once operational, highly charged ions will be loaded from the experimental storage ring ESR into the HITRAP facility, where they are decelerated and cooled. The kinetic energy of the initially fast ions is reduced by more than fourteen orders of magnitude and their thermal energy is cooled to cryogenic temperatures. The cold ions are then delivered to a broad range of atomic physics experiments.

Trapping and cooling techniques have become very important for many fundamental experiments in atomic physics. When applied to highly charged ions confined in Penning traps, these procedures are very effective for testing quantum electrodynamics in extreme electromagnetic fields produced by heavy highly charged ions such as uranium U$^{91+}$. In addition, fundamental constants or nuclear ground state properties can be determined with high accuracy in these simple systems. Finally, by studying a single trapped radioactive ion, its nuclear decay can be studied in detail by observing the disappearance of the signal of the mother and the appearance of that of the daughter isotope. Such experiments on highly charged ions at extremely low energy will become possible by the HITRAP facility which is currently being built up at GSI. Also the future Facility for Antiproton and Ion Research (FAIR) will be briefly described which is expected to be operational by 2014.