Programm für das Wintersemester 2019/2020
Fridays, 14 Uhr c.t.
Ort: Institut für Physik, LorentzRaum (05127), Staudingerweg 7
31.10.19  Prof. Dr. Stephen D. Hogan, Department of Physics and Astronomy, University College London, UK  
Rydberg states, the bound quantum states of an attractive 1/r potential, play a central role in many precision spectroscopic tests of fundamental physics with atoms and molecules, e.g., [1,2]. As perhaps the simplest Rydberg system, the positronium atom  composed of an electron bound to its antiparticle the positron, and therefore a purely leptonic system described almost entirely by bound state QED theory  offers unique opportunities for studies of this kind. However, because of its short groundstate annihilation lifetime (142 ns) many precision experiments with positronium must be performed with longerlived excited states  Rydberg states. The efficient preparation of Rydberg states in positronium is now possible following developments in positron beam and trap technologies [3], and the motion of the atoms excited to these states can be controlled and manipulated using inhomogeneous electric fields through the methods of RydbergStark deceleration [4]. In this talk I will describe new precision microwave spectroscopic measurements of the triplet n=2 fine structure in positronium that takes advantage of these developments. I will also present a new technique for performing matterwave interferometry with atoms in Rydberg states that has been developed using helium atoms [5], but in the future could be exploited for accurate gravity measurements with Rydberg positronium.
[1] A. Beyer, L. Maisenbacher, A. Matveev, R. Pohl, K. Khabarova, A. Grinin, T. Lamour, D. C. Yost, Th. W. Hänsch, N. Kolachevsky, and Th. Udem, The Rydberg constant and proton size from atomic hydrogen, Science 358, 79 (2017) [2] N. Hölsch, M. Beyer, E. J. Salumbides, K. S. E. Eikema, W. Ubachs, Ch. Jungen, and F. Merkt, Benchmarking Theory with an Improved Measurement of the Ionization and Dissociation Energies of H2, Phys. Rev. Lett. 122, 103002 (2019) [3] T. E. Wall, A. M. Alonso, B. S. Cooper, A. Deller, S. D. Hogan, and D. B. Cassidy, Selective Production of RydbergStark States of Positronium, Phys. Rev. Lett. 114, 173001 (2015) [4] S. D. Hogan, RydbergStark deceleration of atoms and molecules, EPJ Techniques and Instrumentation 3, 1 (2016) [5] J. E. Palmer and S. D. Hogan, Electric Rydbergatom interferometry, Phys. Rev. Lett. 122, 250404 (2019)
 

08.11.19  Dr. Stephan Schlamminger, National Institute of Standards and Technology, Gaithersburg, USA  
Up to May 20th this year, there was one mass on earth that we knew with absolute precision, i.e., zero uncertainty. This mass was the international prototype of the kilogram. Since May 20th, it is just another mass and thew mass unit is now defined via a fixed value of the Planck constant, h=6.62607015×〖10〗^(34) "J s" with zero uncertainty. In this presentation, I will explain how the unit of mass can be realized at the kilogram scale via the Kibble balance and the Xray crystal density method. In the present SI, it is, however, no longer necessary to realize the unit at the cardinal point of 1 kg, it can be realized at any scale. The talk will present some future possibilities of this scale invariant definition of the mass unit.  
Sondertermin  Bitte um Beachtung! 
14.11.19  Dr. Johannes W. Deiglmayr, FelixBloch Institute, Universität Leipzig  
Exciting an atom or molecule into a highlying electronic state, a Rydberg state, changes its properties in a drastic, but very wellunderstood way. While the binding energy of the Rydberg electron decrease with the principal quantum number n as 1/n^2, the orbital radius and transition dipole moments increase as n^2. This results in the electric polarizability increasing as n^7. I will present recent experiments in which we have exploited these scaling laws and exaggerated properties to perform precision measurements of ionization energies with relative accuracies up to 10^11, to characterize precisely static and alternating electric fields, and to reduce the detrimental role of stray fields in applications of Rydberg atoms. In a second part, I’ll discuss our progress towards extracting accurate scattering phase shifts from the spectroscopy of heteronuclear longrange Rydberg molecules, which are bound by the interaction of the Rydberg electron with groundstate atoms within its orbit, and how we plan to exploit the exotic properties of longrange Rydberg molecules to create ultracold, strongly correlated plasmas.  

28.11.19  Dr. Juan Manuel CornejoGarcia, Institut für Quantenoptik, Universität Hannover  
Cosmological observations point to an apparent imbalance of matter and antimatter in our universe, which contrasts with the nearly perfect symmetry arising on the level of single particles. Tests for hypothetical limits to this symmetry rest on high precision comparisons of the fundamental properties of particles and antiparticles  for example, with measurements of the proton and antiproton gfactors in Penning traps. However, these measurements rely on cooling and detections schemes that are highly sensitive on the particle's motional energy [1,2].
In this talk, it will be shown an alternative experimental method which enables a speed up of the particles' preparation and a boost in readout fidelity in the respective experiments [3]. Our method allows for sympathetic cooling of a proton or antiproton to its quantum mechanical ground state and provides readout of their spin state, by means of coupling to a laser cooled 9Be+ ion cotrapped in a double well potential. In addition, an overview of the current experimental setup featuring a cryogenic Penning trap stack for first demonstrations of motional coupling between two 9Be+ ions will be presented.
[1] C. Smorra et al., Nature 550, 371374 (2017) [2] G. Schneider et al., Science 358, 10811084 (2017) [3] D. J. Wineland et al., J. Res. NIST 103, 259328 (1998)
 

12.12.19  Dr. Guillaume Salomon, MaxPlanckInstitut für Quantenoptik, Garching  
Developing new approaches to study quantum manybody systems is of fundamental importance in various felds of physics ranging from high energy and condensed matter physics to quantum information and quantum computation. It also holds promise for a better understanding of materials, such as highTc superconductors, and faulttolerant quantum computing which could strongly impact our modern societies. Ultracold atoms have emerged as versatile and well controlled platforms to study fundamental problems in quantum manybody physics. In particular, spinresolved quantum gas microscopy enables to probe strongly correlated fermions with a resolution down to the single particle and offers fascinating opportunities for experiments. I will detail here this technique and discuss our recent experimental studies of the interplay between magnetism and doping in the FermiHubbard model, a minimal model for highTc superconductivity.
 

19.12.19  Prof. Dr. Sile Nic Chormaic, OIST Graduate University, Okinawa, Japan  
Ultrathin optical fibres, with diameters on the order of the propagating light wavelength, have already proven their versatility across a variety of different areas, such as sensing, particle manipulation, cold atom physics, and as optical couplers. The intense evanescent field at the fibre waist is one of the main advantages offered by these systems as it allows us to achieve ultrahigh light intensities that may otherwise not be attainable in a standard laboratory. In this talk, I will present work conducted at OIST with particular focus on our work on optical nanofibremediated multiphoton processes for the generation of highly excited Rydberg atoms and for exploring some other effects, such as quadrupole transitions and stimulated emission from Rb atoms. Overall, the versatility of these fibres for many different experimental platforms particularly if one goes beyond the basic, single mode fibre design will be promoted.  

09.01.20  Jun.Prof. Dr. Jamir Marino, Institut für Physik, Universität Mainz  
The talk will discuss instances of dynamical phases of interacting quantum many body models where coherent and dissipative dynamics occur on equal footing, shaping novel nonequilibrium phase diagrams. The first part of the talk will discuss longrange interacting quantum simulators where an external periodically driven field can stabilise phases without equilibrium counterpart against instabilities triggered by many body quantum fluctuations. In the second part, I will present an instance of ‘cold' time crystal occurring in open quantum systems, where neither MBL or prethermalisation are required to stabilise a strongly interacting nonequilibrium steady state. Time permitting, I will advertise some novel results on a purely dissipative analogue of longrange interacting quantum simulators, which can be implemented in quantum optics or solid state platforms.  

15.01.20  Brian Rost and Lorenzo Del Re , Georgetown, USA  
The driven dissipative many body problem is one of the longest standing unsolved problems in physics and it has experienced a renewed interest in the last decade. In fact, dissipation has been theoretically proposed as a resource for quantum computation and experimentally has been demonstrated that it can be employed to prepare maximally entangled states.
Thus, quantum computers could shed some light on the unsolved problem of drivendissipative quantum systems but there are many choices for how one engineers the reservoir. An attractive approach is to integrate the bath degrees of freedom out via a master equation. Here we show how accurate this approach is by comparing it to an exact solution in the case of a tightbinding dissipativedriven model of fermions coupled to an external fermionic bath, and how to actually simulate it on a currently available IBM quantum computer. We also address the case of an interacting dissipativedriven finite size system, i.e. a threesite Hubbard model with onsite interaction driven by an external field and coupled to a bath. Here, we obtain many of the qualitative features already displayed in the thermodynamic limit. The biggest challenge in implementing these ideas on current quantum computers lies with the need for partial resetting of qubits. We discuss strategies to implement on commercially available hardware and what might be possible with academic machines (such as those available at Mainz).
 
Sondertermin und ort 
16.01.20  Shane P. Kelly, Theoretical Division, LANL, Los Alamos, USA  
In recent years, many experimental platforms have succeeded in producing quantumsystems that, on relevant time scales, are completely isolated from an environment.
This opens the possibility of observing equilibrium states that are not described by standard thermal ensembles and long time dynamics that indefinitely maintain memory of initial states.
In this talk, I discuss two mechanisms for this to occur: many body localization (MBL) and a novel mechanism which occurs in the semiclassical limit of a large spin.
In the first part of my talk, I will discuss the phenomenon of MBL in a disordered spin chain and its effects when coupled to a small environment.
We model this small environment as a clean spin chain and find that, under sufficient coupling and disorder, the dirty chain can induce an MBL effect in the clean chain.
In the second part of my talk, I will discuss the dynamics of a large spin evolving with a nonlinear hamiltonian.
Using semiclassical techniques, we identify when the spin does and does not thermalize.
In doing so, we find a novel mechanism for the breakdown of thermalization based on the slow dynamics of an unstable fixed point.
 

20.01.20  Dr. Guanghua Du, Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, China  
When heavy ion beam with energy from MeV to GeV is incident on the target material, the target material distributed along the ion trajectory will be excited or ionized, which will cause lattice damage, polymer chain break or crosslinking in the material and then result in nanoscale latent track, cluster damage and single event effect. The high energy microbeam facility of Lanzhou National Laboratory of Heavy Ion Accelerator is the highest energy microbeam system in the world which uses tripletquadrupole magnets to produce micron sized high energy ion beams of up to several GeVs. This talk first introduces the accelerator complex and nuclear physics activity at Lanzhou National Lab, and then focuses on the interdisciplinary application of the high energy microbeam facility, including single event effect studies, single ion hitting, nanomaterials, and biomedical studies.  
Sondertermin und ort 
23.01.20  Dr. Maria Chekhova, Institut für Optik, Information und Photonik, Universität Erlangen  
Spontaneous parametric downconversion is the workhorse of quantum optics. This process is used to generate entangled photon pairs and heralded single photons. When strongly pumped, spontaneous parametric downconversion generates so many photon pairs that they overlap and form radiation with almost laser brightness. Despite being bright, this radiation manifests nonclassical effects: quadrature squeezing, photonnumber correlations, and macroscopic entanglement. It has no coherent component and can be considered as amplified vacuum noise; it is therefore often called bright squeezed vacuum. In addition, strong photonnumber fluctuations of bright squeezed vacuum make it extremely efficient for pumping multiphoton effects.
My talk will cover this and other applications of strongly pumped parametric downconversion. In addition, I will talk about the other extreme case of this process. Namely, if photon pairs are generated in a very thin nonlinear layer, the process does not require phase matching – in other words, the momentum of the pump photon is not conserved by the daughter photons. To demonstrate this, I will show the results of generating photon pairs from a 300 nm layer. This nanoscale generation of entangled photons offers unique radiative characteristics: the frequencyangular spectrum is extremely broad and as such it promises subwavelength and subcycle twophoton correlation widths in position and time, respectively. Additionally, it gives an insight into the subwavelength resonances for vacuum fluctuations.
 

30.01.20  Prof. Dr. Philipp Haslinger, Atominstitut, TU Wien, Österreich  
Atom interferometry has proven within the last decades its surprising versatility to sense with high precision tiniest forces. In this talk I will give an overview of our recent work using an optical cavity enhanced atom interferometer to sense with gravitational strength for fifths forces [1,2] and for an on the firstplace counterintuitive inertial property of blackbody radiation [3].
Blackbody (thermal) radiation is emitted by objects at finite temperature with an outward energymomentum flow, which exerts an outward radiation pressure. At room temperature e. g. a cesium atom scatters on average less than one of these blackbody radiation photons every 10^8 years. Thus, it is generally assumed that any scattering force exerted on atoms by such radiation is negligible. However, particles also interact coherently with the thermal electromagnetic field [4] and this leads to a surprisingly strong force acting in the opposite direction of the radiation pressure [3].
If dark energy, which drives the accelerated expansion of the universe, consists of a light scalar field it might be detectable as a “fifth force” between normalmatter objects. In order to be consistent with cosmological observations and laboratory experiments, some leading theories use a screening mechanism to suppress this interaction. However, atominterferometry presents a tool to reduce this screening [5] on socalled chameleon models [6]. By sensing the gravitational acceleration of a 0.19 kg in vacuum source mass which is 10^8 times weaker than Earth´s gravity, we reach a natural bound for cosmological motivated scalar field theories and were able to place tight constraints [1,2].
[1] P. Hamilton, M. Jaffe, P. Haslinger, Q. Simmons, H. Müller, J. Khoury, Atominterferometry constraints on dark energy, Science. 349 (2015) 849–851.
[2] M. Jaffe, P. Haslinger, V. Xu, P. Hamilton, A. Upadhye, B. Elder, J. Khoury, H. Müller, Testing subgravitational forces on atoms from a miniature, invacuum source mass, Nat. Phys. 13 (2017) 938–942.
[3] P. Haslinger, M. Jaffe, V. Xu, O. Schwartz, M. Sonnleitner, M. RitschMarte, H. Ritsch, H. Müller, Attractive force on atoms due to blackbody radiation, Nat. Phys. 14 (2018) 257–260.
[4] M. Sonnleitner, M. RitschMarte, H. Ritsch, Attractive Optical Forces from Blackbody Radiation, Phys. Rev. Lett. 111 (2013) 23601.
[5] C. Burrage, E.J. Copeland, E.A. Hinds, Probing dark energy with atom interferometry, J. Cosmol. Astropart. Phys. 2015 (2015) 042–042. doi:10.1088/14757516/2015/03/042.
[6] B. Elder, J. Khoury, P. Haslinger, M. Jaffe, H. Müller, P. Hamilton, Chameleon dark energy and atom interferometry, Phys. Rev. D. 94 (2016) 44051.
 

Koordination:  
Prof. Dr. Klaus Wendt 