Discovering the microscopic composition of dark matter is one of the most important open problems in physics today. Axions are a leading candidate to be dark matter; however, a search of the full range of all likely axion masses is hampered by the standard quantum noise limit. This makes haloscope searches for axions with masses above 0.1 meV unfeasible with current technologies. To overcome this limitation, we propose a new photon counting technique designed to operate at 30-60 GHz for detecting axions with masses between 0.124 meV and 0.248 meV, based on a single electron in a Penning trap. The electron cyclotron mode absorbs microwave photons, and, via the continuous Stern-Gerlach effect, this absorption imparts a measurable phase shift onto the axial motion. In this paper, we comprehensively analyze this photon detection method. We introduce a new type of fast, phase-sensitive axial detection technique, using axial-magnetron parametric amplification to overcome detector Johnson noise and cancel associated frequency shifts. This method may find other applications in precision Penning trap frequency measurements. We compare the efficiency of the electron single-photon counter with an ideal device, and find that our proposed photon counter has sufficient performance to search for high mass axions.

We demonstrate efficient subthermal cooling of the modified cyclotron mode of a single trapped antiproton and reach particle temperatures T + = E+/k(B) below 200 mK in preparation times shorter than 500 s. This corresponds to the fastest resistive single-particle cyclotron cooling to subthermal temperatures ever demonstrated. By cooling trapped particles to such low energies, we demonstrate the detection of antiproton spin transitions with an error rate < 0.000023, more than 3 orders of magnitude better than in previous best experiments. This method has enormous impact on multi-Penning-trap experiments that measure magnetic moments with single nuclear spins for tests of matter and antimatter symmetry, high- precision mass spectrometry, and measurements of electron g factors bound to highly charged ions that test quantum electrodynamics and establish standards for magnetometry.

The antiproton is a basic constituent of antimatter and required for stringent matter-antimatter comparisons to test the fundamental charge-parity-time (CPT) reversal invariance in the Standard Model of particle physics (1). Using low energy antiprotons, only available at the antimatter factory (AMF) located at CERN (2), such tests have been realized for example in the high-precision spectroscopy of antiprotonic atoms (3), and antihydrogen (4). In our cryogenic Penning-trap experiments (5), we measure the fundamental properties of protons and antiprotons and conduct CPT tests comparing their magnetic moments with a precision of 1.5 parts per billion (6, 7), as well as the most precise test of CPT invariance in the baryon sector by comparing their charge-to-mass ratios to a relative uncertainty of 16 parts-per-trillion(8). Although innovative shielding systems have been implemented (9), our experiments are limited by magnetic field fluctuations imposed by the accelerators in the AMF. To push the limits of our measurements, we are advancing the relocation of antiprotons to dedicated precision laboratories. This work presents a critical milestone in this endeavor: the successful transport of a trapped proton cloud from the AMF using BASE-STEP (10) — a transportable, superconducting, persistent, autonomous, and open Penning-trap system. We transferred the trapped protons from our experimental area at the AMF onto a truck and transported them across CERN’s Meyrin site. We demonstrated loss-free proton relocation, sustaining autonomous operation without external power for four hours, thereby confirming the feasibility of transferring particles to low-noise laboratory environments. The transport range of this system can be extended using mobile power generators (11) to reach laboratories throughout Europe. Our achievement represents a breakthrough and a potential start of a new era in precision antimatter research by conducting antiproton spectroscopy in low-noise laboratories. It also enables transportation and offline studies of other exotic ions, such as highly-charged ions produced in accelerators (12) or high-end EBITs (13), and the charged antimatter ions H¯ + (14) and H¯2 (15)

We demonstrate a new temperature record for image-current mediated sympathetic cooling of a single proton in a cryogenic Penning trap by laser-cooled $^9$Be$^+$. An axial mode temperature of 170 mK is reached, which is a 15-fold improvement compared to the previous best value. Our cooling technique is applicable to any charged particle, so that the measurements presented here constitute a milestone towards the next generation of high-precision Penning-trap measurements with exotic particles.

In the near future BabyIAXO will be the most powerful axion helioscope, relying on a custom-made magnet of two bores of 70 cm diameter and 10 m long, with a total available magnetic volume of more than 7 m(3). In this document, it proposes and describe the implementation of low-frequency axion haloscope setups suitable for operation inside the BabyIAXO magnet. The RADES proposal has a potential sensitivity to the axion-photon coupling g(alpha gamma) down to values corresponding to the KSVZ model, in the (currently unexplored) mass range between 1 and 2 mu eV, after a total effective exposure of 440 days. This mass range is covered by the use of four differently dimensioned 5-meter-long cavities, equipped with a tuning mechanism based on inner turning plates. A setup like the one proposed will also allow an exploration of the same mass range for hidden photons coupled to photons. An additional complementary apparatus is proposed using LC circuits and exploring the low energy range (approximate to 10(-4)-10(-1)mu eV). The setup includes a cryostat and cooling system to cool down the BabyIAXO bore down to about 5 K, as well as an appropriate low-noise signal amplification and detection chain.

The BASE collaboration at the antiproton decelerator/ELENA facility of CERN compares the fundamental properties of protons and antiprotons with ultra-high precision. Using advanced Penning trap systems, we have measured the proton and antiproton magnetic moments with fractional uncertainties of 300 parts in a trillion (p.p.t.) and 1.5 parts in a billion (p.p.b.), respectively. The combined measurements improve the resolution of the previous best test in that sector by more than a factor of 3000. Very recently, we have compared the antiproton/proton charge-to-mass ratios with a fractional precision of 16 p.p.t., which improved the previous best measurement by a factor of 4.3. These results allowed us also to perform a differential matter/antimatter clock comparison test to limits better than 3

Currently, the world's only 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 fundamental interactions and their symmetries. However, 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 charge, parity, and time-reversal 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 detection systems, and the differential pumping section to suppress the residual gas flow into the cryogenic trap chamber.

We present a fluorescence-detection system for laser-cooled Be-9(+) ions based on silicon photomultipliers (SiPMs) operated at 4 K and integrated into our cryogenic 1.9 T multi-Penning-trap system. Our approach enables fluorescence detection in a hermetically sealed cryogenic Penning-trap chamber with limited optical access, where state-of-the-art detection using a telescope and photomultipliers at room temperature would be extremely difficult. We characterize the properties of the SiPM in a cryocooler at 4 K, where we measure a dark count rate below 1 s(-1) and a detection efficiency of 2.5(3)%. We further discuss the design of our cryogenic fluorescence-detection trap and analyze the performance of our detection system by fluorescence spectroscopy of 9Be+ ion clouds during several runs of our sympathetic laser-cooling experiment.

We present the design and characterization of a cryogenic window based on an ultra-thin aluminized biaxially oriented polyethylene terephthalate foil at T < 10 K, which can withstand a pressure difference larger than 1 bar at a leak rate <1×10-9 mbar l/s. Its thickness of ∼1.7 μm makes it transparent to various types of particles over a broad energy range. To optimize the transfer of 100 keV antiprotons through the window, we tested the degrading properties of different aluminum coated polymer foils of thicknesses between 900 and 2160 nm, concluding that 1760 nm foil decelerates antiprotons to an average energy of 5 keV. We have also explicitly studied the permeation as a function of coating thickness and temperature and have performed extensive thermal and mechanical endurance and stress tests. Our final design integrated into the experiment has an effective open surface consisting of seven holes with a diameter of 1 mm and will transmit up to 2.5% of the injected 100 keV antiproton beam delivered by the Antiproton Decelerator and Extra Low ENergy Antiproton ring facility of CERN.

We present a fluorescence-detection system for laser-cooled 9Be+ ions based on silicon photomultipliers (SiPM) operated at 4 K and integrated into our cryogenic 1.9 T multi-Penning-trap system. Our approach enables fluorescence detection in a hermetically-sealed cryogenic Penning-trap chamber with limited optical access, where state-of-the-art detection using a telescope and photomultipliers at room temperature would be extremely difficult. We characterize the properties of the SiPM in a cryocooler at 4 K, where we measure a dark count rate below 1/s and a detection efficiency of 2.5(3) %. We further discuss the design of our cryogenic fluorescence-detection trap, and analyze the performance of our detection system by fluorescence spectroscopy of 9Be+ ion clouds during several runs of our experiment.

The Standard Model (SM) of particle physics is both incredibly successful and glaringly incomplete. Among the questions left open is the striking imbalance of matter and antimatter in the observable universe which inspires experiments to compare the fundamental properties of matter/antimatter conjugates with high precision. Our experiments deal with direct investigations of the fundamental properties of protons and antiprotons, performing spectroscopy in advanced cryogenic Penning-trap systems. For instance, we compared the proton/antiproton magnetic moments with 1.5 ppb fractional precision, which improved upon previous best measurements by a factor of >3000. Here we report on a new comparison of the proton/antiproton charge-to-mass ratios with a fractional uncertainty of 16ppt. Our result is based on the combination of four independent long term studies, recorded in a total time span of 1.5 years. We use different measurement methods and experimental setups incorporating different systematic effects. The final result, $-(q/m)_{\mathrm{p}}/(q/m)_{\bar{\mathrm{p}}}$ = $1.000\,000\,000\,003 (16)$, is consistent with the fundamental charge-parity-time (CPT) reversal invariance, and improves the precision of our previous best measurement by a factor of 4.3. The measurement tests the SM at an energy scale of $1.96\cdot10^{-27}\,$GeV (C$.$L$.$ 0.68), and improves 10 coefficients of the Standard Model Extension (SME). Our cyclotron-clock-study also constrains hypothetical interactions mediating violations of the clock weak equivalence principle (WEP$_\text{cc}$) for antimatter to a level of $|\alpha_{g}-1| < 1.8 \cdot 10^{-7}$, and enables the first differential test of the WEP$_\text{cc}$ using antiprotons \cite{hughes1991constraints}. From this interpretation we constrain the differential WEP$_\text{cc}$-violating coefficient to $|\alpha_{g,D}-1|<0.030$.

The standard model of particle physics is both incredibly successful and glaringly incomplete. Among the questions left open is the striking imbalance of matter and antimatter in the observable universe 1 , which inspires experiments to compare the fundamental properties of matter/antimatter conjugates with high precision 2 – 5 . Our experiments deal with direct investigations of the fundamental properties of protons and antiprotons, performing spectroscopy in advanced cryogenic Penning trap systems 6 . For instance, we previously compared the proton/antiproton magnetic moments with 1.5 parts per billion fractional precision 7 , 8 , which improved upon previous best measurements 9 by a factor of greater than 3,000. Here we report on a new comparison of the proton/antiproton charge-to-mass ratios with a fractional uncertainty of 16 parts per trillion. Our result is based on the combination of four independent long-term studies, recorded in a total time span of 1.5 years. We use different measurement methods and experimental set-ups incorporating different systematic effects. The final result, -(q/m)_p/(q/m)_p̅=1.000000000003(16) , is consistent with the fundamental charge–parity–time reversal invariance, and improves the precision of our previous best measurement 6 by a factor of 4.3. The measurement tests the standard model at an energy scale of 1.96 × 10 −27 gigaelectronvolts (confidence level 0.68), and improves ten coefficients of the standard model extension 10 . Our cyclotron clock study also constrains hypothetical interactions mediating violations of the clock weak equivalence principle (WEP cc ) for antimatter to less than 1.8 × 10 −7 , and enables the first differential test of the WEP cc using antiprotons 11 . From this interpretation we constrain the differential WEP cc -violating coefficient to less than 0.030.

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.

We describe a newly developed polytetrafluoroethylene/copper capacitor driven by a cryogenic piezoelectric slip-stick stage and demonstrate with the chosen layout cryogenic capacitance tuning of ≈60 pF at ≈10 pF background capacitance. Connected to a highly sensitive superconducting toroidal LC circuit, we demonstrate tuning of the resonant frequency between 345 and 685 kHz, at quality factors Q > 100 000. Connected to a cryogenic ultra low noise amplifier, a frequency tuning range between 520 and 710 kHz is reached, while quality factors Q > 86 000 are achieved. This new device can be used as a versatile image current detector in high-precision Penning-trap experiments or as an LC-circuit-based haloscope detector to search for the conversion of axion-like dark matter to radio-frequency photons. This new development increases the sensitive detection bandwidth of our axion haloscope by a factor of ≈1000.

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.

Efficient cooling of trapped charged particles is essential to many fundamental physics experiments 1,2 , to high-precision metrology 3,4 and to quantum technology 5,6 . Until now, sympathetic cooling has required close-range Coulomb interactions 7,8 , but there has been a sustained desire to bring laser-cooling techniques to particles in macroscopically separated traps 5,9,10 , 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 antiprotons 1 , facilitating improved precision in matter–antimatter comparisons 11 and dark matter searches 12,13 .

The electric dipole moment of the electron (eEDM) can be measured with high precision using heavy polar molecules. In this paper, we report on a series of new techniques that have improved the statistical sensitivity of the YbF eEDM experiment. We increase the number of molecules participating in the experiment by an order of magnitude using a carefully designed optical pumping scheme. We also increase the detection efficiency of these molecules by another order of magnitude using an optical cycling scheme. In addition, we show how to destabilise dark states and reduce backgrounds that otherwise limit the efficiency of these techniques. Together, these improvements allow us to demonstrate a statistical sensitivity of 1.8 × 10 −28 e cm after one day of measurement, which is 1.2 times the shot-noise limit. The techniques presented here are applicable to other high-precision measurements using molecules.