Programm für das Wintersemester 2023/2024
Thursdays, 14 Uhr c.t.
Institut für Physik
IPH Lorentzraum 05127
26.10.23  Prof. Dr. Alexandre Obertelli, TU Darmstadt Institut für Kernphysik  
Rare isotope facilities have given access to the neutronrich side of the nuclear landscape. In this seminar, the recent results obtained at the RIBF, RIKEN, on the structure of the most neutronrich nuclear systems studied so far, 4n and 28O, will be presented together with the challenges faced by ab initio theory. The neutron excess in neutronrich nuclei develop as a neutron skin or halo at the nuclear surface. The extension of neutrons at the nuclear surface remains relatively unconstrained.
The new experiment PUMA (antiProton Unstable Matter Annihilation) at CERN aims at investigating the neutron to proton content of the nuclear density tail of stable and unstable nuclei by use of trapped antiprotons as a probe. The principle and status of the experiment will be given.  
14:00 Uhr s.t., IPH Lorentzraum 05127  

02.11.23  Prof. Dr. Jörn MüllerQuade, KIT Karlsruhe Kryptographie & Sicherheit  
Classical cryptographic tasks, like key distribution, need computational assumptions and are vulnerable to attacks breaking these assumptions in the future. Classical security is not everlasting. For key distribution Quantum Cryptography offers a huge advantage, unconditionally secure protocols are possible. This success, however, could not be repeated for other important cryptographic tasks, e.g. bit commitment or coin tossing. What is more, it could even be proven that all cryptographic tasks which are sufficent for confidential computing cannot be realized with unconditional security even if a quantum channel is available. This nogo result overshadowed the research on confidential computing with quantum cryptography and the term quantum cryptography is now largely seen as a synonym for quantum key distribution.
This talk shows that in spite of the nogo theorems there still are advantages of quantum cryptography over classical solutions. In particular the talk will present a yet unpublished result, that under therealistic assumption that quantum storage has a limited lifetime “everlasting security” can be achieved. I.e. computational assumptions are still needed, but the cryptographic protocol eventually becomes unconditionally secure after the quantum information used has decayed.  
14:00 Uhr s.t., IPH Lorentzraum 05127  

09.11.23  Dr. Hendrik Poulsen Nautrup & Dr. Sofiène Jerbi, Universität Innsbruck Institut für Theoretische Physik  
Measurementbased quantum computation (MBQC) offers a fundamentally unique paradigm to design quantum algorithms. Indeed, due to the inherent randomness of quantum measurements, the natural operations in MBQC are not deterministic and unitary, but are rather augmented with probabilistic byproducts. Yet, the main algorithmic use of MBQC so far has been to completely counteract this probabilistic nature in order to simulate unitary computations expressed in the circuit model.
In this talk, we are going to introduce MBQC as an ansatz for parameterized learning models that embraces this inherent randomness and treat random byproducts in MBQC as a resource for computation. We demonstrate numerically, that such models can lead to significant gains in learning performance in certain generative modeling tasks. We finish with a proposal for an experimental implementation of such an MBQCbased learning model for shuttlingbased ion traps.  
14:00 Uhr s.t., IPH Lorentzraum 05127  

16.11.23  Prof. Dr. Wilfried Nörtershäuser, TU Darmstadt Institut für Kernphysik  
Nuclear charge radii of radioactive isotopes are typically referenced to a stable nucleus in the isotopic chain through an atomic isotope shift measurement. In some cases, this can limit the uncertainty of the obtained charge radii of radioactive nuclei to the uncertainty of the reference measurements from elastic electron scattering or muonic atom spectroscopy. To overcome this limit in light mass nuclei like 10,11B, an alloptical approach for the charge radius determination purely from laser spectroscopy measurements and nonrelativistic QED calculations was tested with the wellknown nucleus of 12C through laser excitation of heliumlike 12C4+ from the metastable 2 3S1 state with a lifetime of 21 ms to the 2 3P𝐽 states. The highprecision collinear laser spectroscopy of 12C4+ has been performed at the Collinear Apparatus for Laser Spectroscopy and Applied Physics (COALA) at at TU Darmstadt in the Institute of Nuclear Physics and meanwhile extended to 13C4+.
I will give an overview of the project and present the results including the extracted alloptical nuclear charge radius of 12C. An outlook on planned measurements at COALA and a potential application on shortlived isotopes at ISOLDE will be provided.
This project is supported by DFG (ProjectID 279384907  SFB 1245).  
14:00 Uhr s.t., IPH Lorentzraum 05127  

23.11.23  Dr. Nils Huntemann, PTB Nationales Metrologieinstitut  
The 171Yb+ ion features two narrow optical transitions: an electric octupole (E3) transition as well as an electric quadrupole (E2) transition. Both transitions are suitable for the realization of an optical clock and accepted as secondary representations of the SI unit second and a composite system that relies on the spectroscopic information provided by both transitions can even provide superior clock performance.
Because both transitions also show a large differential sensitivity to the fine structure constant á, its possible variations can be probed by comparing the transition frequencies at various positions in spacetime. We find improved bounds on a linear temporal drift of á, as well as its coupling to the gravitational potential of the sun, from a longterm optical clock comparison [1,2]. Additionally, the couplings of socalled ultralight bosonic dark matter (m « 1 eV/c^2) to standard model particles would lead to coherent oscillations of constants, with an oscillation frequency corresponding to the Compton frequency of the dark matter mass [3]. We conduct a broadband darkmatter search by comparing the frequency of the E3 transition to that of the E2 transition, and to that of the 1S0 ↔ 3P0 transition in 87Sr. We find no indication for significant oscillations in our experimental data. Consequently, we put limits on oscillations of the finestructure constant and thus improve existing bounds on the scalar coupling of ultralight dark matter to photons for darkmatter masses of about 1E−24 to 1E−17 eV/c^2 [2]. Couplings to quarks and gluons can also be investigated with optical frequency ratio measurements by considering the effect an oscillating nuclear charge radius would have on electronic transitions [4].
Finally, I will report on our efforts towards clocks in which cotrapped 88Sr+ ions [5] enable even superior 171Yb+ clock performance.
[1] Lange et al., Phys. Rev. Lett. 126, 011102 (2021).
[2] Filzinger et al., Phys. Rev. Lett. 130, 253001 (2023).
[3] Arvanitaki et al., Phys. Rev. D 91, 015015 (2015).
[4] Banerjee et al., arXiv:2301.10784 (2023).
[5] Steinel et al., Phys. Rev. Lett. 131, 083002 (2023).  
14:00 Uhr s.t., IPH Lorentzraum 05127  

30.11.23  Prof. Dr. Catalina Curceanu, INFN, Rom/Italy  
We are experimentally investigating possible departures from the standard quantum mechanics’ predictions at the Gran Sasso underground laboratory in Italy.
In particular, with refined radiation detectors, we are searching signals predicted by the dynamical collapse models (spontaneous emission of radiation) which were proposed to solve the “measurement problem” in quantum physics, and signals indicating a possible violation of the Pauli Exclusion Principle.
I shall discuss our recent results which ruled out the natural parameterfree version of the gravityrelated collapse model. I shall then present more generic results on testing CSL (Continuous Spontaneous Localization) collapse models and discuss future perspectives.
Finally, I shall present the VIP experiment, with which we search for possible violations of the Pauli Exclusion Principle manifested as “impossible” atomic transitions, and muse about the impact of this research in relation to Quantum Gravity models.  
14:00 Uhr s.t., IPH Lorentzraum 05127  

07.12.23  Dr.Ing. Steffen Kurth, Fraunhofer Institut for Electronic Nano Systems ENAS  
The ion trap chip is considered to be the heart of quantum computing based on trapped ions. An ideal case is to have available a devices with all subcomponents that are necessary for the operation in a small package. First approaches to fabricated integrated miniaturized ion traps are followed by different groups worldwide. Latest directions are to combine multiple registers, that are connected to each other, to use micro optical components such as micro lenses or even photonic integrated circuits for coupling laser radiation to the ions, to integrate photo detectors (e.g. single photon avalanche diodes) close to or within the ion trap chip. The integration of electronic components (e.g. digital/analogconverters) to provide the electric potentials for the trap electrodes is a further goal that becomes an enabler for integrated ion traps with a higher number of registers.
This talk will show how wafer level micro technologies contribute to the above described target. It starts with the vision of an integrated ion trap. Wafer level technologies for fabricating of the different layers are discussed. It covers different material deposition procedures and etching. A next section is about optical subcomponents and their manufacturing procedures. Furthermore, a broad variety of assembly technologies and of ways for electric signal routing and connecting is shown with examples.  
14:00 Uhr s.t., IPH Lorentzraum 05127  

21.12.23  Prof. Jörg Pretz, Forschungszentrum Jülich  
Electric Dipole Moments (EDMs) of elementary particles, including hadrons, are considered as one of the most powerful tool to study CPviolation beyond the Standard Model. Such CPviolating mechanisms are searched for to explain the dominance of matter over antimatter in our universe. Hypothetical dark matter particles, like axions or axionlikeparticles, induce an oscillating EDM. EDMs of charged particles can be measured in storage rings. Due to an EDM, the spin vector will experience a torque resulting in a change of the original spin direction which can be determined with the help of a polarimeter. Although the principle of the measurement is simple, the smallness of the expected effect makes this a challenging experiment requiring new developments in various experimental areas.
The talk will focus on first results obtained at the Cooler Synchrotron COSY at Forschungszentrum Jülich and will also discuss future plans.  
14:00 Uhr s.t., IPH Lorentzraum 05127  

11.01.24  Prof. Dr. Stefan Eriksson, Department of Physics, Faculty of Science and Engineering, Swansea University, UK  
Precision measurements of the properties of trapped antihydrogen offer stringent tests of fundamental principles underlying particle physics and general relativity, such as Lorentz and CPT invariance and the Einstein Equivalence Principle. In this presentation I will give an overview of the ALPHA antihydrogen experiment at CERN including recent results from spectroscopy and observations of the effect of gravity. I will review how results are interpreted as tests of fundamental physics with a discussion of how a hypothetical CPT violation could result in matterantimatter asymmetry. I will give an outline of the prospects for future highprecision spectroscopy, freefall and gravitational redshift experiments with antihydrogen.  
14:00 Uhr s.t., IPH Lorentzraum 05127  

25.01.24  Dr. Aleksandra Zoilkowska, JGU NEUQUAM Research Group  
Cold atom experiments offer a distinctive platform for the investigation of manybody quantum physics, especially in nonequilibrium scenarios. The complexity inherent in these experiments often poses challenges to conventional theoretical methods. Nevertheless, exact analytical solutions become feasible when the underlying theory is integrable. Integrability plays a pivotal role in constraining the dynamics of manybody systems, enabling the derivation of, for instance, precise timedependent density and velocity profiles after inhomogeneous quenches. This unique characteristic establishes a direct correspondence between theoretical predictions and experimental outcomes.
In this talk, I will delve into the essence of quantum integrability and its efficacy in nonequilibrium manybody calculations, utilizing the framework of Generalized Hydrodynamics. An examination of the LiebLiniger Hamiltonian will exemplify how integrability has been applied in cold atom setups, resulting in the experimental realization of Quantum Newton's Cradle. Furthermore, I will draw upon my own research to provide insights into other quantum ''beasts'' emerging in outofequilibrium physics, rooted in an integrable theory known as the Homogeneous SineGordon Model.  
14:00 Uhr s.t., IPH Lorentzraum 05127  

01.02.24  Prof. Piet van Duppen, KU Leuven, Belgien  
The thorium229 nucleus contains an isomeric state with a low excitation energy, making it possible to probe using lasers. It is one of the best candidates for the development of a nuclear clock [1,2] which will enable the ability to test fundamental principles in physics (see e.g. [4]). However, to accomplish such a nuclear clock, the nuclear properties of the isomer need to be determined more precisely and two approaches are being followed.
VUV spectroscopy revealed the radiative decay of the thorium229 isomer in a study at ISOLDECERN by populating the isomer via the beta decay of actinium229, implanting the beam in large bandgap crystals (CaF2 and MgF2). A reduced uncertainty of the isomer’s excitation energy (8.338±0.024 eV) and a first determination of the halflife (670±102 s) in MgF2 was reported [5]. During a followup campaign, different crystals were tested, the energy was determined with a better precision and the halflife behaviour of the VUV signal in the different crystals was studied.
Preparatory work to perform laser ionization spectroscopy of the thorium229 ground and isomeric states, populated in the alpha decay of uranium233, is performed in an argon gasjet based system. These studies, aimed to deduce the meansquare charge radii and moments of both ground and isomeric state, are based on singly charged thorium ions and necessitates a search for efficient and effective laser ionization schemes of thorium giving rise to a more precise determination of the first and second ionization potential. Results from these off and online studies will be presented and outlook to future work discussed.
[1] E. Peik and C. Tamm, EPL 61, 181 (2003).
[2] C. Campbell et al., Phys. Rev. Lett. 108, 120802 (2012).
[3] L. von der Wense et al. Nature 533 (7601), 47–51 (2016).
[4] E. Peik et al., Quantum Sci. Technol. 6, 034002 (2021).
[5] Kraemer et al., Nature 617, 706–710 (2023).  
14:00 Uhr s.t., IPH Lorentzraum 05127  

08.02.24  Prof. J.C. Séamus Davis, University of Oxford, Oxford, UK  
Although UTe2 appears to be the first 3D spintriplet topological superconductor, its superconductive orderparameter Δ_k has not yet been established. If spintriplet, it should have odd parity so that Δ_(k)=Δ_k and, in addition, may break timereversal symmetry. A distinctive identifier of 3D spintriplet topological superconductors is the appearance of an Andreev bound state (ABS) on all surfaces parallel to a nodal axis, due to the presence of a topological surface band (TSB). Moreover, theory shows that specific ABS characteristics observable in tunneling to an swave superconductor distinguish between chiral and nonchiral Δ_k. To search for such phenomena in UTe2 we employ swave superconductive scantip imaging of UTe2 [1] to discover a powerful zeroenergy ABS signature at the (011) crystal termination [2]. Its imaging yields quasiparticle scattering interference signatures of two Δ_k nodes aligned with the crystal aaxis. Most critically, development of the zeroenergy Andreev conductance peak into two finiteenergy particlehole symmetric conductance maxima as the tunnel barrier is reduced, signifies that UTe2 superconductivity is nonchiral. Overall, the discovery of a TSB, of its a zeroenergy ABS, of internodal scattering along the aaxis, and of splitting the zeroenergy Andreev conductance maximum due to swave proximity, categorizes the superconductive Δ_k as the oddparity nonchiral B3u state [2], which is equivalent to the planar state of superfluid 3He.
[1] Nature 618, 921 (2023)
[3] Gu, Wang, et al. Science (2023)  
14:00 Uhr s.t., IPH Lorentzraum 05127  

Koordination:  Kontakt: 
Dr. Christian Smorra Dr. Lars von der Wense  Andrea Graham 