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The riddle of the baryon asymmetry, i.e. the matter antimatter imbalance in the universe can be addressed by comparing matter particles with their antimatter counterparts. At the antiproton decelerator (AD) at CERN several antimatter experiments investigate whether CPT (charge-parity-time reversal) invariance and the WEP (weak equivalence principle) hold. The systems probed are antihydrogen ( H ¯ ), antiprotonic helium and individual antiprotons ( p ¯ ). This article is meant to give an overview of the experiments located at the AD, discuss some commonly used experimental techniques and point out what the different experimental approaches entail. The research done on low-energy antimatter systems can be seen as complementary to the high energy research carried out at CERN and elsewhere: It provides bounds on CPT invariance and directly addresses the question of whether the WEP holds for antimatter. It is noted that the AD - at the moment - is the only low-energy antiproton source on earth.

Compact optical atomic clocks have become increasingly important in field applications and clock networks. Systems based on Ramsey-Bordé interferometry (RBI) with a thermal atomic beam seem promising to fill a technology gap in optical atomic clocks, as they offer higher stability than optical vapour cell clocks while being less complex than cold atomic clocks. Here, we demonstrate RBI with strontium atoms, utilizing the narrow intercombination line at 689 nm, yielding a 60 kHz broad spectral feature. The obtained Ramsey fringes for varying laser power are analyzed and compared with a numerical model. The transition at 461 nm is used for fluorescence detection. Analyzing the slope of the RBI signal and the fluorescence detection noise yields an estimated short-term stability of < 4 × 10 − 14 / τ / 1 s . We present our experimental setup in detail, including the atomic beam source, frequency-modulation spectroscopy to lock the 461 nm laser, laser power stabilization and the high-finesse cavity pre-stabilization of the 689 nm laser. Our system serves as a ground testbed for future clock systems in mobile and space applications.

Abstract We describe a multi-step “rotating wall” compression of a mixed cold antiproton–electron non-neutral plasma in a 4.46 T Penning–Malmberg trap developed in the context of the AEḡIS experiment at CERN. Such traps are routinely used for the preparation of cold antiprotons suitable for antihydrogen production. A tenfold antiproton radius compression has been achieved, with a minimum antiproton radius of only 0.17 mm. We describe the experimental conditions necessary to perform such a compression: minimizing the tails of the electron density distribution is paramount to ensure that the antiproton density distribution follows that of the electrons. Such electron density tails are remnants of rotating wall compression and in many cases can remain unnoticed. We observe that the compression dynamics for a pure electron plasma behaves the same way as that of a mixed antiproton and electron plasma. Thanks to this optimized compression method and the high single shot antiproton catching efficiency, we observe for the first time cold and dense non-neutral antiproton plasmas with particle densities n ≥ 1013 m−3, which pave the way for an efficient pulsed antihydrogen production in AEḡIS. Graphical abstract

The AEgIS experiment aims at producing antihydrogen (and eventually measuring the effects of the Earth gravitational field on it) with a method based on the charge exchange reaction between antiproton and Rydberg positronium. To be precise, antiprotons are delivered by the CERN Antiproton Decelerator (AD) and are trapped in a multi-ring Penning trap, while positronium is produced by a nanoporous silica target and is excited to Rydberg states by means of a two steps laser excitation. New Monte Carlo simulations are presented in this paper in order to investigate the current status of the AEgIS experiment [1] and to interpret the recently collected data [2].

Compact optical atomic clocks have become increasingly important in field applications and clock networks. Systems based on Ramsey-Borde interferometry (RBI) with a thermal atomic beam seem promising to fill a technology gap in optical atomic clocks, as they offer higher stability than optical vapour cell clocks while being less complex than cold atomic clocks. Here, we demonstrate RBI with strontium atoms, utilizing the narrow 1S0 -> 3P1 intercombination line at 689 nm, yielding a 60 kHz broad spectral feature. The obtained Ramsey fringes for varying laser power are analyzed and compared with a numerical model. The 1S0 -> 1P1 transition at 461 nm is used for fluorescence detection. Analyzing the slope of the RBI signal and the fluorescence detection noise yields an estimated short-term stability of 4x10-14 / sqrttau. We present our experimental setup in detail, including the atomic beam source, frequency-modulation spectroscopy to lock the 461 nm laser, laser power stabilization and the high-finesse cavity pre-stabilization of the 689 nm laser. Our system serves as a ground testbed for future clock systems in mobile and space applications.

Compact optical atomic clocks have become increasingly important in field applications and clock networks. Systems based on Ramsey-Borde interferometry (RBI) with a thermal atomic beam seem promising to fill a technology gap in optical atomic clocks, as they offer higher stability than optical vapour cell clocks while being less complex than cold atomic clocks. Here, we demonstrate RBI with strontium atoms, utilizing the narrow 1S0 -> 3P1 intercombination line at 689 nm, yielding a 60 kHz broad spectral feature. The obtained Ramsey fringes for varying laser power are analyzed and compared with a numerical model. The 1S0 -> 1P1 transition at 461 nm is used for fluorescence detection. Analyzing the slope of the RBI signal and the fluorescence detection noise yields an estimated short-term stability of 4x10-14 / sqrttau. We present our experimental setup in detail, including the atomic beam source, frequency-modulation spectroscopy to lock the 461 nm laser, laser power stabilization and the high-finesse cavity pre-stabilization of the 689 nm laser. Our system serves as a ground testbed for future clock systems in mobile and space applications.