Design and commissioning of an experiment for sympathetic cooling and coupling of ions in a cryogenic Penning trap

Precise comparisons between the properties of matter and antimatter conjugates constitute a stringent test of CPT and Lorentz symmetries. The proton’s and antiproton’s magnetic moments have recently been measured to high precision in Penning traps, but further progress is impaired by the need to prepare a particle with low motional energy. Current preparation schemes require long preparation times and are limited by high temperatures. Sympathetic laser cooling using an atomic ion has been proposed for preparation of low-energy protons and antipro- tons. This thesis presents the design and commissioning of a cryogenic Penning trap system for sympathetic laser cooling using beryllium ions. The experiment aims to demonstrate direct Coulomb coupling between two particles trapped in nearby, but separate potential wells in a Penning trap stack for the first time. This technique could be used for sympathetic cooling of particles lacking the necessary substructure to apply laser cooling directly. The application of this method on protons and antiprotons has the potential to decrease the mean kinetic energies of the particles and the preparation times required by several orders of magnitude. Furthermore, the method can be extended to other particles, such as highly charged ions. A quantum logic spectroscopy scheme for the measurement of the magnetic moment of the proton and antiproton has been proposed by Heinzen and Wineland. Experimental requirements for realisation of this proposal are discussed. The design of a suitable Penning trap system is described. A cryogenic ultra-high vacuum system cooled by a closed-cycle cryocooler, equipped with an ultra low vibration interface, is designed and commissioned. The necessary infrastructure, such as laser systems and electronics are described. First signals taken from this newly constructed cryogenic Penning trap are presented. Laser ablation trap loading, Doppler cooling and the reduction of the particle number down to a single ion are demonstrated. Prospects of the experiment and implications for the precision of future measurements of the proton’s and antiproton’s magnetic moments augmented by sympathetic laser cooling and elements of quantum logic are discussed

Elementary laser-less quantum logic operations with (anti-)protons in Penning traps

Static magnetic field gradients superimposed on the electromagnetic trapping potential of a Penning trap can be used to implement laser-less spin-motion couplings that allow the realization of elementary quantum logic operations in the radio-frequency regime. An important scenario of practical interest is the application to $g$-factor measurements with single (anti-)protons to test the fundamental charge, parity, time reversal (CPT) invariance as pursued in the BASE collaboration [Smorra et al., Eur. Phys. J. Spec. Top. 224, 3055-3108 (2015), Smorra et al., Nature 550, 371-374 (2017), Schneider et al., Science 358, 1081-1084 (2017)]. We discuss the classical and quantum behavior of a charged particle in a Penning trap with a superimposed magnetic field gradient. Using analytic and numerical calculations, we find that it is possible to carry out a SWAP gate between the spin and the motional qubit of a single (anti-)proton with high fidelity, provided the particle has been initialized in the motional ground state. We discuss the implications of our findings for the realization of quantum logic spectroscopy in this system.Comment: 10 pages, 4 figures, 1 table; published versio

Optical stimulated-Raman sideband spectroscopy of a single 9Be+ ion in a Penning trap

We demonstrate optical sideband spectroscopy of a single 9Be+ ion in a cryogenic 5 tesla Penning trap using two-photon stimulated-Raman transitions between the two Zeeman sublevels of the 1s22s ground state manifold. By applying two complementary coupling schemes, we accurately measure Raman resonances with and without contributions from motional sidebands. From the latter we obtain an axial sideband spectrum with an effective mode temperature of (3.1±0.4) mK. These results are a key step for quantum logic operations in Penning traps, applicable to high-precision matter-antimatter comparison tests in the baryonic sector of the standard model

Resolved-sideband cooling of a single 9^9Be+^+ ion in a Penning trap

Manipulating individual trapped ions at the single quantum level has become standard practice in radio-frequency ion traps, enabling applications from quantum information processing to precision metrology. The key ingredient is ground-state cooling of the particle's motion through resolved-sideband laser cooling. Ultra-high-presicion experiments using Penning ion traps will greatly benefit from the reduction of systematic errors offered by full motional control, with applications to atomic masses and $g$-factor measurements, determinations of fundamental constants or related tests of fundamental physics. In addition, it will allow to implement quantum logic spectroscopy, a technique that has enabled a new class of precision measurements in radio-frequency ion traps. Here we demonstrate resolved-sideband laser cooling of the axial motion of a single $^9$Be$^+$ ion in a cryogenic 5 Tesla Penning trap system using a two-photon stimulated-Raman process, reaching a mean phonon number of $\bar{n}_z = 0.10(4)$. This is a fundamental step in the implementation of quantum logic spectroscopy for matter-antimatter comparison tests in the baryonic sector of the Standard Model and a key step towards improved precision experiments in Penning traps operating at the quantum limit.Comment: 6 pages, 5 figure

Quantum logic inspired techniques for spacetime-symmetry tests with (anti-)protons

Cosmological observations as well as theoretical approaches to physics beyond the standard model provide strong motivations for experimental tests of fundamental symmetries, such as CPT invariance. In this context, the availability of cold baryonic antimatter at CERN has opened an avenue for ultrahigh-precision comparisons of protons and antiprotons in Penning traps. This work discusses an experimental method inspired by quantum logic techniques that will improve particle localization and readout speed in such experiments. The method allows for sympathetic cooling of the (anti-)proton to its quantum-mechanical ground state as well as the readout of its spin alignment, replacing the commonly used continuous Stern–Gerlach effect. Both of these features are achieved through coupling to a laser-cooled 'logic' ion co-trapped in a double-well potential. This technique will boost the measurement sampling rate and will thus provide results with lower statistical uncertainty, contributing to stringent searches for time dependent variations in the data. Such measurements ultimately yield extremely high sensitivities to CPT violating coefficients acting on baryons in the standard-model extension, will allow the exploration of previously unmeasured types of symmetry violations, and will enable antimatter-based axion-like dark matter searches with improved mass resolution