Physikalisches Kolloquium

Metastable antiprotonic helium is an exotic atom composed of a helium nucleus, electron, and an antiproton. It is among the hadron-antihadron systems with the longest known lifetimes. Laser light can be used to excite atomic transitions involving the antiproton orbital. By utilizing sub-Doppler two-photon laser spectroscopy and buffer gas cooling, its atomic transition frequencies were measured to ppb-scale precision. Comparisons with the results of QED calculations allowed the antiproton-to-electron mass ratio to be determined as 1836.1526734(15). The results were used to set upper limits on fifth forces between antiprotons and nucleons at atomic length scales, and on forces that may arise between an electron and antiproton mediated by hypothetical bosons. Efforts are currently underway to improve the experimental precision using CERN’s ELENA facility. We also observed narrow spectral lines of these atoms formed in superfluid helium with a surprisingly high spectral resolution of 2 parts per million. This revealed the hyperfine structure arising from the spin interaction between the antiproton and electron, despite the atom being surrounded by a dense matrix of normal atoms. Metastable pionic helium (πHe+) contains a negative pion occupying a state of n≈l-1≈17, and retains a 7 ns average lifetime. We recently used the 590 MeV ring cyclotron facility of Paul Scherrer Institute to synthesize the atoms, and irradiated them with infrared laser pulses. This induced a pionic transition within the atom and the π- being absorbed into the helium nucleus. This constitutes the first laser excitation and spectroscopy of an atom containing a meson. By improving the experimental precision, the pion mass may be determined to a high precision as in the antiproton case.

High performance computing, many-body methods with polynomial scaling, and ideas from effective-field-theory is pushing the frontier of ab-initio computations of nuclei. Here I report on advances in coupled-cluster computations of nuclei starting from chiral Hamiltonians with two- and three-nucleon forces. The ab-initio approach can now be used to address fundamental questions related to the nature of the neutrino by accurate computations of neutrino-less double beta decay and making first steps towards neutrino-nucleus scattering on relevant nuclei. Global surveys of bulk properties of medium-mass and neutron- rich nuclei from ab-initio approaches are now possible by using reference states that break rotational symmetry. These calculations have revealed systematic trends of charge radii in various isotopic chains, questioned the existence of certain magic shell closures in neutron-rich nuclei, and confrontation with data have exposed challenges for ab- initio theory. By restoring rotational symmetry, we have made predictions for the rotational structure of neutron-rich neon isotopes including 32,34Ne. In addition to entire regions of the nuclear chart now being targeted by ab-initio computations, entirely new ways to make quantified predictions are becoming possible by the development of accurate emulators of ab-initio calculations. These emulators reduce the computational cost by many orders of magnitude allowing for billions of simulations of nuclei using modest computing resources. This allows us to perform global sensitivity analysis, quantify uncertainties, and use novel statistical tools in predicting properties of nuclei. Recently we used these tools to make a quantified prediction of the neutron skin in 208Pb, and found that the neutron-skin is smaller and more precise than a recent extraction from parity-violating electron scattering but in agreement with other experimental probes. We have also used these tools to address the questions of what drives deformation in atomic nuclei and whether 28O is a bound nucleus. These developments demonstrate how realistic two- and three-nucleon forces act in atomic nuclei and allow us to make quantitative predictions across the nuclear landscape.

The development of atomic quantum simulation platforms has led to the creation of a new generation of programmable quantum simulators that can be scaled to large particle numbers while maintaining a certain degree of programmability. This talk reports on theory-experiment collaborative work using trapped ion platforms with up to fifty-one qubits/spins, where we develop and demonstrate quantum protocols that can address questions ranging from fundamental to practical. Examples include first observation of area law vs. volume law entanglement in ground and excited states of many-body systems, and quantum simulators acting as programable quantum sensors implementing near “optimal” entanglement-enhanced quantum metrology.

Thanks to its strong immunity to environmental perturbations, for many decades, molecular nuclear systems have found extensive applications in science, technology, and medicine. One of the techniques exploring these nuclear-spin systems is the technique of nuclear magnetic resonance (NMR). While typically performed under very strong magnetic fields (>1 T), recent advances in hyperpolarization methods and magnetometric techniques have led to the emergence of a technique of zero- and ultralow-field (ZULF) NMR. Operation under such unique conditions, with simple, small, and cost-efficient experimental systems, has opened up new avenues for ultraprecise spectroscopy and relaxometry, allowing for interesting applications in chemistry and biology. In physics, ZULF NMR was used for the engineering of long-lived (tens of seconds) nuclear states and the searches for physics beyond the Standard Model. Despite these applications, however, the technique is still at its early stage and many applications will be developed in future. During the colloquium, the fundamentals and distinctive features of ZULF NMR will be presented and some of its applications will be highlighted.

The groundbreaking discovery of the neutron star merger event GW170817 ushered in a new era of multimessenger astrophysics. One key observation was the optical signal that accompanied GW170817, which provided the first firm proof that neutron star mergers produce heavy elements. Still, it is not known exactly which elements are produced by mergers and in what proportions. Are neutron star mergers the sole astrophysical source of the heaviest elements or do other extreme events contribute? A full understanding of neutron star mergers and their role in galactic chemical evolution requires progress in a number of areas including nuclear physics. Thousands of exotic nuclear species participate in neutron star merger nucleosynthesis, and their properties shape abundance patterns and kilonova signals. Here we discuss how nuclear physics uncertainties influence predictions of nucleosynthesis observables. We then explore the promise of experimental campaigns at rare isotope beam facilities to both reduce these uncertainties and provide insight into astrophysical environments of heavy element production.

Plasmonics is commonly used to confine electromagnetic waves into subwavelength noble metal structures for photonic applications. As an unwanted side effect, heat is generated locally, which is the foundation of thermoplasmonics. Besides numerous very interdisciplinary applications, such local heat generation provides unique dynamic control over microscopic objects in liquids with non-equilibrium physics. I will give two examples. First, I discuss experiments on active colloidal particles that are self-propelled by thermoplasmonic effects. Such active particles mimic the motility of living species like bacteria but lack the feedback loops that control their behavior. The optical control of plasmonic heating allows us to implement feedback loops, behavior and even learning for active particles. Using this technique, we can show that perception-reaction delays as omnipresent in living systems can be the origin of a variety of dynamical collective states that even display signatures of criticality. In a second example, I will briefly report on experiments using plasmonic heat generation to enable the control of liquids and macromolecules. Dynamic temperature fields thereby help us to study elementary processes of peptide aggregation as relevant for neurodegenerative diseases over extremely long periods of time.

Controlled manipulation of a system allows for systematic investigation of the underlying interactions and phenomena. Simultaneously, tunability also enables the development of novel materials systems and devices customized for specific applications. Here, we will focus on materials systems that conventionally have not been used as active components in spintronic devices. We will explore the impact of strain on the antiferromagnetic domain structure via magneto-elastic coupling1. Furthermore, we will delve into hybrid molecule-magnetic interfaces. Molecules offer a unique way of controlling and varying the structure at the interface making it possible to precisely tune the spin injection and diffusion by molecular design2. In particular, chirality has gained recent interest in the context of the chiral-induced spin selectivity effect3. Here, we will explore signatures of spin filtering at a non-magnetic chiral molecule-metal interface paving the path toward novel hybrid spintronics.

Questions that drive searches for physics beyond the Standard Model include the physical origin of the cosmic baryon asymmetry and of dark matter. Quark dynamics, as realized through the theory of quantum chromodynamics (QCD), can appear in these studies in very different ways. In this talk, I develop these possibilities explicitly, first describing the role of QCD in ultra-sensitive searches for new physics, particularly at low energies, and then turning to how its features could be exploited in describing the undiscovered universe, along with the essential observational and experimental tests that could confirm them.

Magnetic fields of planets, stars and galaxies are generated by the homogeneous dynamo effect, or self-excitation, in moving electrically conducting fluids, such as liquid metals or plasmas. Once generated, magnetic fields can promote cosmic structure formation by destabilizing, via the magnetorotational instability (MRI), rotational flows that would be otherwise hydrodynamically stable. Closely related instabilities, such as the current-driven Tayler instability might be at work in the solar tachocline. For a long time, these topics had been the subject of purely theoretical and numerical research. This situation changed in 1999 when the threshold of magnetic-field self-excitation was exceeded in the two liquid sodium experiments in Riga and Karlsruhe. Since 2006, the VKS dynamo experiment in Cadarache has successfully reproduced many features of geophysical interest such as reversals and excursions. MRI related experiments were partly successful with the observation of the helical MRI and the azimuthal MRI at Helmholtz-Zentrum Dresden-Rossendorf (HZDR), where first evidence of the current-driven Tayler instability in a liquid metal was obtained, too. In another liquid metal experiment at the Dresden High Magnetic Field laboratory (HLD) the “magic point” of coinciding Alfvén and sound speeds was reached, which is thought to play a key role for the heating of the solar corona. The lecture gives an overview about previous and future liquid metal experiments on dynamo action and magnetically triggered flow instabilities, with special focus on the precession driven liquid sodium experiment and the large-scale MRI experiment that are under construction in the framework of the DRESDYN project at HZDR. Particular emphasis is placed on generic questions such as the reversal mechanism of the geodynamo and the possibility of a planetary synchronization of the solar dynamo, on which those experiments might shed some fresh light.

Small satellites are nowadays extremely powerful, flexible and sustainable platforms that can be used to complement the missions usually assigned to larger spacecrafts. Modularity, standardization, intensive use of state-of-the art COTS technologies consent to prepare cheaper missions in shorter timeframes, thus allowing a more frequent access to space environment, including Cislunar and Interplanetary. The Italian Space Agency – ASI promotes, funds and coordinates the national initiatives also in this promising sector, both for national missions and within international cooperation. The first products of this effort are ArgoMoon and LICIACube, both 6U cubesats which operated during 2022 as first Italian spacecrafts beyond the Low Earth Orbit. The Light Italian Cubesat for Imaging of Asteroids - LICIACube participated in the NASA Double Asteroid Redirection Test - DART mission, the first active Planetary Defense mission; on September 26th 2022, few minutes after DART’s impact on asteroid Dimorphos, LICIACube captured unique images of the impact effects, primarily the plume of ejecta, and the not visible side of the secondary asteroid. The operations have been conducted by a national team coordinated by ASI. The design, manufacturing, testing and operations of the space and ground segment elements have been performed by the Italian firm Argotec under ASI management, while a wide scientific team supported the investigation preparation with impact modelling simulation and data analysis and interpretation, under the coordination of the National Institute of Astrophysics INAF. The engineering teams of Polytechnic of Milan and University of Bologna were in charge of trajectory design and optimization and the orbit determination and navigation, respectively. Captured images during the challenging fly-by confirmed the DART success as Planetary Defense initiative and provided scientists with highly valuable data, that allowed a first set of results to be confirmed and are currently under further analysis for scientific investigations. In fact, on October 11th 2022, NASA announced the complete success of the DART mission, confirming that the spacecraft’s impact altered Dimorphos’ orbit around Didymos by 32 minutes. Moreover, The LICIACube images show that the DART impact on Dimorphos generated a cone of ejected surface material with a large aperture angle. This plume has a complex and inhomogeneous structure, characterized by non-radial filaments, dust grains, and single and clustered boulders that allows us to deeply investigate the nature of the ejecta and the structure of Dimorphos.

Coherent elastic neutrino-nucleus scattering (CEvNS) is a process in which a neutrino scatters off an entire nucleus. It is tremendously challenging to detect, due to the tiny nuclear recoil. CEvNS was measured for the first time by the COHERENT collaboration using the unique source of neutrinos at the Oak Ridge National Laboratory Spallation Neutron Source. This talk will describe the physics reach of CEvNS, as well as COHERENT's measurements, status and future plans.

Quantum electrodynamics (QED) is part of the standard model and the best understood quantum field theory. Many tests exist, from free particles (electron and muon anomalous magnetic moment) to bound states. From the historical measurement of the Lamb-shift which lead to the advent of QED and field theories, many systems have been studied and compared to the most advanced calculations. One can cite hydrogen, positronium, muonium, highly charged, few electron ions[1] and exotic atoms (atoms in which the electron is replaced by a heavier particle like a muon, a pion or an antiproton). In this talk I will present a few cases of highly charged ions high-precision results (few ppm accuracy) obtained with our Double Crystal Spectrometer in Paris[2-4] for medium-Z elements, and preliminary results obtained at GSI on few-electron uranium. I will then present new ideas [5] and first demonstration results on QED tests using muonic atoms and transition-edge sensor micro-calorimeter at JPARC [6, 7], and their extension to antiprotonic atoms at ELENA in the future. Detailed comparison with QED and relativistic many-body calculations when relevant will be made. [1]Topical Review: QED tests with highly-charged ions, P. Indelicato. J. Phys. B 52, 232001 (2019). [2]High-precision measurements of n=2->n=1 transition energies and level widths in He- and Be-like Argon Ions, J. Machado, C.I. Szabo, J.P. Santos et al. Phys. Rev. A 97, 032517 (2018). [3]Reference-free measurements of the 1s 2s 2p 2P1/2,3/2 → 1s2 2s 2S1/2 and 1s 2s 2p 4P5/2 → 1s2 2s 2S1/2 transition energies and widths in lithiumlike sulfur and argon ions, J. Machado, G. Bian, N. Paul et al. Phys. Rev. A 101, 062505 (2020). [4]Absolute measurement of the relativistic magnetic dipole transition in He-like sulfur, J. Machado, N. Paul, G. Soum-Sidikov et al. Phys. Rev. A in press, (2023). [5]Testing Quantum Electrodynamics with Exotic Atoms, N. Paul, G. Bian, T. Azuma et al. Phys. Rev. Lett. 126, 173001 (2021). [6]Deexcitation Dynamics of Muonic Atoms Revealed by High-Precision Spectroscopy of Electronic K X Rays, T. Okumura, T. Azuma, D.A. Bennett et al. Phys. Rev. Lett. 127, 053001 (2021). [7]Proof-of-Principle Experiment for Testing Strong-Field Quantum Electrodynamics with Exotic Atoms: High Precision X-ray Spectroscopy of Muonic Neon, T. Okumura, T. Azuma, D.A. Bennett et al. Phys. Rev. Lett. in press, (2023).

Magnetic field sensors have a mature and transversal level of implementation in the market, from automotive to biomedical domains. The impressive technological progress in thin film preparation and characterization, combined with nano-microfabrication tools offer presently large spectra for device design. The materials discussed include several varieties of thin film materials combined onto multilayer stacks. In addition, the noise mechanisms (the “killing factor” that limits the MR sensor performance) will be discussed, and I will show successful strategies for improving the signal-to-noise ratio, improving the ultimate field detectable by an MR sensor. Examples where spintronic sensors are useful tools for precision sensing will be provided, including integration with microfluidics, optical and MEMS micromachined actuators. During my talk, I will show how challenging applications have identified creative solutions, requiring joint skills in transversal areas as physics, materials, electronics and mechanical engineering.

Research on and with ions has been the subject of current scientific activities for some time. In particular, heavy ions with very different particle energies are of increasing interest. The provision of electrically charged "heavy" particle fluxes of high density and the acceleration of these particle beams is therefore of particular importance and has grown into an almost independent focus of research and development. In the talk, a brief outline of the past development of key technologies for accelerating heavy ions, especially in linear accelerators, will be given. The heavy ion linear accelerator at GSI in Darmstadt has to be upgraded for the future as a synchrotron-injector for highest intensities. In addition, the HElmholtz LInear ACcelerator HELIAC, a superconducting accelerator with the highest continuous wave intensities for heavy ion beams in the medium energy segment, is currently being designed and construction has already begun. These brand-new developments will also be presented. Die Forschung an und mit Ionen ist seit längere Zeit Gegenstand aktueller wissenschaftlicher Aktivitäten. Insbesondere schwere Ionen mit sehr unterschiedlicher Teilchenenergie sind dabei von zunehmendem Interesse. Die Bereitstellung elektrisch geladener "schwerer" Teilchenflüsse hoher Dichte und der Beschleunigung dieser Teilchenstrahlen kommt daher besondere Bedeutung zu und ist zu einem fast eigenständigen Schwerpunkt der Forschung und Entwicklung gewachsen. Im Vortrag soll ein kurzer Abriss der vergangenen Entwicklung der Schlüsseltechnologien zur Beschleunigung schwere Ionen insbesondere in Linear-beschleunigern gegeben werden. Der Schwerionenlinearbeschleuniger der GSI in Darmstadt muss für die Zukunft als Synchrotron-Injektor für höchste Intensitäten aufgerüstet werden. Darüber hinaus wird zurzeit mit dem HElmholtz LInear ACcelerator HELIAC ein supraleitender Beschleuniger mit höchstem Dauerstrichintensitäten für Schwerionenstrahlen im mittleren Energiesegment konzipiert und auch bereits begonnen zu bauen. Diese brandaktuellen Neuentwicklungen sollen ebenfalls dargestellt werden.