We constrain the coupling between axionlike particles (ALPs) and photons, measured with the superconducting resonant detection circuit of a cryogenic Penning trap. By searching the noise spectrum of our fixed-frequency resonant circuit for peaks caused by dark matter ALPs converting into photons in the strong magnetic field of the Penning-trap magnet, we are able to constrain the coupling of ALPs with masses around 2.7906-2.7914  neV/c^{2} to g_{aγ}<1×10^{-11}  GeV^{-1}. This is more than one order of magnitude lower than the best laboratory haloscope and approximately 5 times lower than the CERN axion solar telescope (CAST), setting limits in a mass and coupling range which is not constrained by astrophysical observations. Our approach can be extended to many other Penning-trap experiments and has the potential to provide broad limits in the low ALP mass range.

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.

A superconducting self-shielding three-solenoid system with an adjustable shielding factor is developed, implemented, and characterized using a single antiproton in a Penning trap. With the tuned system, we suppress external magnetic field disturbances by up to a factor of 225 +/- 15, allowing antiproton-to-proton charge-to-mass ratio comparisons with fourfold reduced frequency fluctuations and antiproton magnetic moment determinations with tenfold reduced uncertainty.

High-precision comparisons of the proton-to-antiproton charge-to-mass ratios provide sensitive tests of the fundamental charge, parity, time (CPT) invariance. In 2014, we performed such a measurement with a fractional precision of 69parts in a trillion (p.p.t.). In this article, we describe technical developments which were implemented to improve the precision of our previous measurement by at least a factor of 3.

Precise comparisons of the fundamental properties of protons and antiprotons, such as magnetic moments and charge-to-mass ratios, provide stringent tests of CPT invariance, and thus, matter-antimatter symmetry. Using advanced Penning-trap methods, we have recently determined the magnetic moments of the proton and the antiproton with a relative precision of 0.3 p.p.b. and 1.5 p.p.b., respectively [1, 2]. Both experiments rely on sub-thermal cooling of the particle’s modified cyclotron mode using feedback-cooled tuned circuits. This time-consuming process is ultimately required to identify single spin quantum transitions with high detection fidelity, which is a major prerequisite to apply the multi-trap methods that are essential for p.p.b. measurements. Methods of laser cooling achieved unprecedented quantum control of trapped ions. However, they are not directly applicable to our experiments because the proton and antiproton lack the electronic structure required for laser cooling. In order to advance our techniques and to drastically reduce the measurement time, we are currently implementing methods to sympathetically cool protons and antiprotons by coupling them to laser-cooled beryllium ions, using a common endcap method [3]. To this end, our collaboration has developed a new apparatus featuring a common endcap double Penning trap. Based on our calculations we expect that this new apparatus will enable us to prepare single protons and antiprotons with energies close to the Doppler limit of laser cooling within tens of seconds, which will ultimately reduce our particle preparation times by a factor of at least 50 [4]. In this poster we present the experiment and the status of our ongoing efforts to deterministically prepare single protons and antiprotons at mK-temperatures.

We summarize our recent 1.5 parts per billion measurement of the antiproton magnetic moment using the multi Penning-trap system of the BASE collaboration. The result was achieved by combining the detection of individual spin-transitions of a single antiproton with a novel two-particle spectroscopy technique, which dramatically improved the data sampling rate. This measurement contributes to improve the test of the fundamental charge, parity, time reversal (CPT) invariance in the baryon sector by a factor of 350 compared to our last measurement, and by a factor of 3000 compared to the best competing measurement. We review the measurement technique and discuss the improved limits on CPT-violating physics imposed by this measurement.

Precise knowledge of the fundamental properties of the proton is essential for our understanding of atomic structure as well as for precise tests of fundamental symmetries. We report on a direct high-precision measurement of the magnetic moment μp of the proton in units of the nuclear magneton μN The result, μp = 2.79284734462 (±0.00000000082) μN, has a fractional precision of 0.3 parts per billion, improves the previous best measurement by a factor of 11, and is consistent with the currently accepted value. This was achieved with the use of an optimized double-Penning trap technique. Provided a similar measurement of the antiproton magnetic moment can be performed, this result will enable a test of the fundamental symmetry between matter and antimatter in the baryonic sector at the 10-10 level.