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The BASE collaboration at the Antiproton Decelerator facility of CERN compares the fundamental properties of protons and antiprotons using advanced Penning-trap systems. In previous measurement campaigns, we measured the magnetic moments of the proton and the antiproton, reaching (sub-)parts-in-a-billion fractional uncertainty. In the latest campaign, we have compared the proton and antiproton charge-to-mass ratios with a fractional uncertainty of 16 parts in a trillion. In this contribution, we give an overview of the measurement campaign, and detail how its results are used to constrain nine spin-independent coefficients of the Standard-Model Extension in the proton and electron sector., Comment: Presented at the Ninth Meeting on CPT and Lorentz Symmetry, Bloomington, Indiana, May 17-26, 2022

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., Comment: 28 pages, 14 figures

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., Comment: 11 pages, 7 figures

We discuss laser-based and quantum logic inspired cooling and detection methods amenable to single (anti-)protons. These would be applicable e.g. in a g-factor based test of CPT invariance as currently pursued within the BASE collaboration. Towards this end, we explore sympathetic cooling of single (anti-)protons with atomic ions as suggested by Heinzen and Wineland (1990)., Comment: Presented at LEAP 2016 in Kanazawa, Japan

We present methods to manipulate and detect the motional state and the spin state of a single antiproton or proton which are currently under development within the BASE (Baryon Antibaryon Symmetry Experiment) collaboration. These methods include sympathetic laser cooling of a single (anti-)proton using a co-trapped atomic ion as well as quantum logic spectroscopy with the two particles and could be implemented within the collaboration for state preparation and state readout in the antiproton $g$-factor measurement experiment at CERN. In our project, these techniques shall be applied using a single $^9\text{Be}^+$ ion as the atomic ion in a Penning trap system at a magnetic field of 5 T. As an intermediate step, a controlled interaction of two beryllium ions in a double-well potential as well as sympathetic cooling of one ion by the other shall be demonstrated., Comment: Proceedings of the 13th International Conference on Low Energy Antiproton Physics (LEAP 2018) Paris, France, 12-16 March 2018

Current experimental efforts to test the fundamental CPT symmetry with single (anti-)protons are progressing at a rapid pace but are hurt by the nonzero temperature of particles and the difficulty of spin state detection. We describe a laser-based and quantum logic inspired approach to single (anti-)proton cooling and state detection., Comment: Presented at the Seventh Meeting on CPT and Lorentz Symmetry, Bloomington, Indiana, June 20-24, 2016

Current precision experiments with single (anti)protons to test CPT symmetry progress at a rapid pace, but are complicated by the need to cool particles to sub-thermal energies. We describe a cryogenic Penning-trap setup for $^9$Be$^+$ ions designed to allow coupling of single (anti)protons to laser-cooled atomic ions for sympathetic cooling and quantum logic spectroscopy. We report on trapping and laser cooling of clouds and single $^9$Be$^+$ ions. We discuss prospects for a microfabricated trap to allow coupling of single (anti)protons to laser-cooled $^9$Be$^+$ ions for sympathetic laser cooling to sub-mK temperatures on ms time scales., Comment: Presented at the Eighth Meeting on CPT and Lorentz Symmetry, Bloomington, Indiana, May 12-16, 2019

Astrophysical observations indicate that there is roughly five times more dark matter in the Universe than ordinary baryonic matter, with an even larger amount of the Universe's energy content due to dark energy. So far, the microscopic properties of these dark components have remained shrouded in mystery. In addition, even the five percent of ordinary matter in our Universe has yet to be understood, since the Standard Model of particle physics lacks any consistent explanation for the predominance of matter over antimatter. Inspired by these central problems of modern physics, we present here a direct search for interactions of antimatter with dark matter, and place direct constraints on the interaction of ultra-light axion-like particles $-$ one of the dark-matter candidates $-$ and antiprotons. If antiprotons exhibit a stronger coupling to these dark-matter particles than protons, such a CPT-odd coupling could provide a link between dark matter and the baryon asymmetry in the Universe. We analyse spin-flip resonance data acquired with a single antiproton in a Penning trap [Smorra et al., Nature 550, 371 (2017)] in the frequency domain to search for spin-precession effects from ultra-light axions with a characteristic frequency governed by the mass of the underlying particle. Our analysis constrains the axion-antiproton interaction parameter $f_a/C_{\overline{p}}$ to values greater than $0.1$ to $0.6$ GeV in the mass range from $2 \times 10^{-23}$ to $4 \times 10^{-17}\,$eV/$c^2$, improving over astrophysical antiproton bounds by up to five orders of magnitude. In addition, we derive limits on six combinations of previously unconstrained Lorentz-violating and CPT-violating terms of the non-minimal Standard Model Extension., Comment: 26 pages, 7 figures, including supplementary information

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 report on the detection of individual spin quantum transitions of a single trapped antiproton in a Penning trap. The spin-state determination, which is based on the unambiguous detection of axial frequency shifts in presence of a strong magnetic bottle, reaches a fidelity of 92.1$\%$. Spin-state initialization with $>99.9\%$ fidelity and an average initialization time of 24 min are demonstrated. This is a major step towards an antiproton magnetic moment measurement with a relative uncertainty on the part-per-billion level.

We developed highly-sensitive image-current detection systems based on superconducting toroidal coils and ultra-low noise amplifiers for non-destructive measurements of the axial frequencies (550$\sim$800$\,$kHz) of single antiprotons stored in a cryogenic multi-Penning-trap system. The unloaded superconducting tuned circuits show quality factors of up to 500$\,$000, which corresponds to a factor of 10 improvement compared to our previously used solenoidal designs. Connected to ultra-low noise amplifiers and the trap system, signal-to-noise-ratios of 30$\,$dB at quality factors of > 20$\,$000 are achieved. In addition, we have developed a superconducting switch which allows continuous tuning of the detector's quality factor, and to sensitively tune the particle-detector interaction. This allowed us to improve frequency resolution at constant averaging time, which is crucial for single antiproton spin-transition spectroscopy experiments, as well as improved measurements of the proton-to-antiproton charge-to-mass ratio., Comment: 87 (2016) 113305

The Baryon Antibaryon Symmetry Experiment (BASE) aims at performing a stringent test of the combined charge parity and time reversal (CPT) symmetry by comparing the magnetic moments of the proton and the antiproton with high precision. Using single particles in a Penning trap, the proton/antiproton $g$-factors, i.e. the magnetic moment in units of the nuclear magneton, are determined by measuring the respective ratio of the spin-precession frequency to the cyclotron frequency. The spin precession frequency is measured by non-destructive detection of spin quantum transitions using the continuous Stern-Gerlach effect, and the cyclotron frequency is determined from the particle's motional eigenfrequencies in the Penning trap using the invariance theorem. By application of the double Penning-trap method we expect that in our measurements a fractional precision of $\delta g/g$ 10$^{-9}$ can be achieved. The successful application of this method to the antiproton will represent a factor 1000 improvement in the fractional precision of its magnetic moment. The BASE collaboration has constructed and commissioned a new experiment at the Antiproton Decelerator (AD) of CERN. This article describes and summarizes the physical and technical aspects of this new experiment., Comment: This is the presubmission version of this article: http://link.springer.com/article/10.1140%2Fepjst%2Fe2015-02607-4