Austrian Quantum Talks - Archive : austrian_quantum_talks

1 | Title | Speaker | Date | Location | Abstract | Host Name |
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2 | VCQ Colloquium | Ron Folman (Ben Gurion University) | 05.12.2022 | Lise Meitner Lecture Hall, Boltzmanngasse 5 (UNiversity of Vienna) | The Stern-Gerlach effect, found a century ago, has become a paradigm of quantum mechanics. Unexpectedly, until recently, there has been little evidence that the original scheme with freely propagating atoms exposed to gradients from macroscopic magnets is a fully coherent quantum process. Several theoretical studies have explained why a Stern-Gerlach interferometer is a formidable challenge. Here, we provide a detailed account of the realization of a full-loop Stern-Gerlach interferometer for single atoms and use the acquired understanding to show how this setup may be used to realize an interferometer for macroscopic objects doped with a single spin. Such a realization would open the door to a new era of fundamental probes, including the realization of previously inaccessible tests at the interface of quantum mechanics and gravity. | VCQ Admin |

3 | Discrete fluxes, higher-form symmetries and Ward identities | Siye Wu (National Tsing Hua University, Taiwan) | 06.12.2022 | Erwin-Schrödinger-Hörsaal, Boltzmanngasse 5 (University of Vienna) | We study discrete electric and magnetic fluxes in gauge theories from algebraic and topological viewpoints. We explain that they can not be simultaneously specified in a sector of quantum Hilbert space. This is the uncertainty of fluxes discovered previously in Abelian gauge theories. We further interpret the discrete fluxes as charges of higher-form symmetries, which leads to an enhanced understanding of the latter in terms of cohomology groups of spacetime with coefficients in a group. More generally, higher-form symmetries exist whenever there are constant gauge transformations. Finally, we explore the relations to Noetherâ second theorem and higher Ward identities. | S. Fredenhagen, D. Grumiller, E. Battista, R. Ruzziconi |

4 | Advances in subleading power factorization and resummation | Dr Sebastian Jaskiewicz (Inst. for Particle Physics Phenomenolog, Durham University) | 06.12.2022 | Fakultaet fuer Physik, Erwin Schroedinger-HS, Boltzmanngasse 5, 5. Stock | Precise theoretical predictions are a key ingredient in ongoing tests of the Standard Model and in searches for physics beyond it.Since its inception twenty years ago,Soft Collinear Effective Theory(SCET)has been successfully applied to improve the precision of many important observables in collider physics.It is now standard practice to use SCET to derive factorisation theorems and apply renormalisation group (RG) methods to achieve leading power resummation of large logarithms that appear in regions of phase space with disparate energy scales.In this talk,I will discuss the recent advances in taking the step beyond the leading term in the power expansion.Focusing on the threshold Drell-Yan process, I will explain how the general factorisation formula can be derived and I will discuss new objects that emerge beyond leading power: collinear jet functions and generalised soft functions. | A. Hoang, M. Procura, A. Broggio |

5 | Entangling microwaves with optical light | Johannes Fink (IST Austria) | 07.12.2022 | IQOQI Innsbruck, Erwiing Schrödinger hall | Entanglement is 'the characteristic trait' that distinguishes quantum mechanics from previous theories of physics and it is the essential resource behind scaling advantages in emerging quantum technologies. Today, entanglement between similar systems such as photons, ions, atoms, electronic spins or superconducting circuits is routinely generated and used for basic quantum information processing and quantum communication tasks. However, a full-fledged development of such technologies will make it necessary to share this important resource also across very dissimilar physical platforms. Quantum transducers between microwave and optical photons would offer such a capa! bility bu t the ubiquitous trade-off between low efficiencies and added classical noise have so far prevented the observation of genuine non-classical correlations in such devices. Here we show deterministic entanglement of itinerant microwave and optical fields in the continuous variable domain. We achieve this in a millikelvin environment using a superconducting, triply-resonant electro-optical device that is operated in pulsed mode to minimize added noise. The resulting entangled state is squeezed by 0.72 dB below the vacuum level and violates the Duan-Simon separability criterion >5 standard deviations. This establishes a non-classical communication channel between superconducting microwave circuits and telecom wavelength light with wide-ranging implications for quantum technology applications. | Gerhard Kirchmair |

6 | Francesco Intravaia (Humboldt University of Berlin) | 09.10.2022 | The motion of objects in vacuum has fascinated scientists for centuries. Understanding the physics at work in these circumstances has wide fundamental and technological implications, ranging from nanosciences to cosmology. In particular, the last ten years have witnessed an increasing number of investigations addressing nonequilibrium interactions in which the (quantum) electromagnetic fluctuations in vacuum can behave as a viscous medium. Examples are blackbody and quantum friction, i.e., contactless drag forces that hinder the motion of an object aiming at bringing it to rest. Blackbody and quantum friction are the manifestations of a phenomenon that can be called quantum electromagnetic viscosity. Interestingly, a careful and self-consistent theoretical description of this phenomenon revealed to be challenging and predictions have varied widely in the past. Recently, consensus is | Rene Sedmik | ||

7 | Erwin Schroedinger Lecture: Photonic quantum computing -- a bright future for many applications | Prof. Philip Walther (University of Vienna) | 12.12.2022 | Erwin Schroedinger Institut, Boltzmann Lecture Hall | The precise quantum control of single photons, together with the intrinsic advantage of being mobile make optical quantum system ideally suited for quantum information applications that require communication or the delegation of tasks. Examples include quantum cryptography as well as quantum clouds and quantum computer networks. I present the current architectures for scalable photonic quantum computers and special purpose applications that exploit advantages of photonic quantum system. This is shown by examples for various quantum computations such as quantum machine learning and in particular reinforcement learning, in addition to secure quantum and classical computing tasks that require quantum networks. I will discuss technological challenges for the scale up of photonic quantum computers and remarkable opportunities for special-purpose applications such as neuromorphic circuits. | Erwin Schroedinger Institut |

8 | Distracted by Science-Fiction: The Physics of Reverse-Engineered Metrics | Sebastian Schuster (Charles University, Prague) | 13.12.2022 | Erwin-Schrödinger-Hörsaal, Boltzmanngasse 5 (University of Vienna) | Reverse-engineered metrics are ad-hoc metrics; instead of using the Einstein equation to solve for a metric given a stress-energy tensor as input,the metric is the input and the stress-energy tensor the output. Much of the attention is taken up by metrics inspired by science fiction:Wormholes, warp drives, tractor beams. Historically, however, this was not the case, as both the GÃ¶del universe and regular black holes are similarly reverse-engineered.The goal of this talk will be to demonstrate how the mathematical simplicity (differentiation instead of integration) is gained through physical difficulty. Usually this is reduced to a question of physicality.Worse this question is then in turn answered in an oversimplified way by invoking (point-wise) energy conditions. I will demonstrate why energy condition cannot easily separate the physical wheat from the metric chaff and how . . . | S. Fredenhagen, D. Grumiller, E. Battista, R. Ruzziconi |

9 | Thermal fate and many-body parametric resonances in a driven sine Gordon model | Roberta Citro (University of Salerno, IT) | 16.12.2022 | Atominstitut, Hörsaal | Integrable systems are expected to not thermalize, but it is still an open question if interactions and mode coupling at long times can let the system reach the infinite temperature limit. The questions I will address in this talk are how an integrable quantum system breaks the non-ergodicity and undergoes the thermal fate and how the mode coupling appears at long times. I will give some answers for the many-body Kapitza pendulum and the parametric harmonic oscillator, the so-called driven sine-Gordon model. I will also discuss a proposal for experiments with cold atoms. | Jörg Schmiedmayer |

10 | Beyond quantum computation: the physics of can and can’t | Chiara Marletto (Research Fellow at Wolfson College, University of Oxford) | 9.1.2023 | Lise Meitner Lecture Hall, University of Vienna | The theory of the universal quantum computer has brought us rapid technological developments, together with remarkable improvements in how we understand quantum theory. There are, however, reasons to believe that quantum theory may ultimately have to be modified into a new theory: for instance, it will have to be merged with general relativity, to incorporate gravity; and some claim that it may be impossible to have quantum effects beyond a certain macroscopic scale. So what lies ahead of quantum theory, and of the universal quantum computer? To shed some light on these questions, we need a conceptual shift. Specifically, we can harness general principles about possible/impossible transformations, rather than dynamical laws and initial conditions. These general principles are ideal to describe the physics of ‘hybrid quantum systems’ – which include a quantum system interacting with another system whose exact dynamics are intractable or not fully known. I will describe my recent work in developing applications of this new approach to a number of interconnected problems within information theory and thermodynamics. I will also describe a few experimental implementations that I co-designed to illustrate these theoretical ideas. | Časlav Brukner |

11 | 101 Fun Things to Do with a Quantum Entanglement Source | Paul Kwiat (University of Illinois at Urbana-Champaign) | 11.1.2023 | online | The Quantum Information Revolution is in full swing, and entanglement — the spooky nonclassical, nonlocal connection that can be shared by quantum particles — is the key ingredient. In this talkwe’ll discuss how to create (photon) entanglement, and several applications for secure communication and quantum-enhanced sensing. Time permitting, we’ll include a lesson in quantum cooking. | Armando Rastelli |

12 | The Impact of Imperfect Timekeeping on Quantum Computation | Jake Xuereb (TU Wien) | 11.1.2023 | Atominstitut, Hörsaal | In order to unitarily evolve a quantum system, an agent requires knowledge of time, a parameter which no physical clock can ever perfectly characterise. In this talk, I will communicate how limitations on acquiring knowledge of time impact quantum computation. The quality of timekeeping an agent has access to impacts the gate complexity they are able to achieve within a computation. Although some tasks such as cooling a qubit can be achieved using a timer of arbitrary quality for control. To carry out these investigations, I will introduce tick distributions, a tool developed in the field of autonomous quantum clocks [1,2] which allows us to understand the operational performance of a clock and the average gate fidelity of a noisy channel introduced by the randomized benchmarking [3,4] community which allows one to investigate the quality of a quantum computation. Putting these techniques together we'll understand how access to robust timekeeping is essential for accurate quantum computation. [1] - P. Erker, M. T. Mitchison, R. Silva, M. P. Woods, N. Brunner, and M. Huber, Autonomous quantum clocks: Does thermodynamics limit our ability to measure time?, Phys. Rev. X 7, 031022 (2017) [2] - M. P. Woods, Autonomous Ticking Clocks from Axiomatic Principles, Quantum 5, 381 (2021) [3] - J. Emerson, R. Alicki, and K. Zyczkowski, Scalable noise estimation with random unitary operators, Journal of Optics B: Quantum and Semiclassical Optics 7, S347 (2005) [4] - M. A. Nielsen, A simple formula for the average gate fidelity of a quantum dynamical operation, Physics Letters A 303, 249 (2002). | Maximilian Prüfer |

13 | On the Quantum Nature of the Coulombic Interaction | Abhay Ashtekar (The Pennsylvania State University) | 16.1.2023 | Lise Meitner Lecture Hall, University of Vienna | The interface between Quantum Information and Quantum Field Theory – especially Quantum Gravity – is emerging as a forefront area of fundamental physics. But there is some tension between the way the basic concept of ‘locality’ is commonly understood by the two communities. This tension descends to the issues of interpretation of precisely what would be tested by experiments that have been proposed to probe the quantum nature of gravity. Recall that Hilbert spaces H_grav and H_ph of gravitons and photons know only about the ‘radiative modes’ of the gravitational and electromagnetic fields. But matter sour! ces also give rise to ‘Coulombic modes’. Are the ‘Coulombic’ parts of the gravitational and electromagnetic fields produced by quantum matter also quantum mechanical, then? If so, in what sense? The ‘Coulombic modes’ are not even ‘registered’ in the Hilbert spaces H_grav and H_ph! Will the proposed experiments directly test the quantum nature of the ‘radiative aspects’ or ‘Coulombic aspects’? The talk will examine such elementary issues by drawing on an exactly soluble, non-perturbative quantum gravity model that is especially well-suited for this purpose. | Markus Aspelmeyer |

14 | Towards Driving Quantum Systems with the Nonradiating Near-Field of a Modulated Electron Beam | Matthias Kolb (TU Wien) | 18.1.2023 | Atominstitut, Hörsaal | When manipulating quantum systems with electromagnetic radiation, the spatial resolution is usually constrained by the diffraction limit. To overcome this limitation, we have developed a fundamentally new approach, in which we attempt to coherently transmit electromagnetic excitation through the nonradiating near-field of a modulated electron beam. This could open a path to spectrally selective quantum control with nanoscale spatial resolution by exploiting the small de Broglie wavelength of electrons. In a proof of principle experiment we will use a spatially modulated electron beam generated by a fast cathode ray tube from an analog oscilloscope to coherently drive the hyperfine levels of potassium [1]. To also show coherent manipulation of a solid state quantum system, we are currently striving to perform Electron Spin Resonance with a BDPA sample. In this experimental realization a microcoil is used to detect the decay of the excited spins. The deflection of the electron beam in two dimensions might allow for generating optimized painted potentials. References: [1] D. Rätzel, D. Hartley, O. Schwartz, and P. Haslinger, “Controlling Quantum systems with modulated electron beams”, Phys. Rev. Research 3, 023247 (2021) | Maximilian Prüfer |

15 | Towards coupling an atom array to an optical cavity | Stephan Roschinsky (TU Wien) | 25.1.2023 | Atominstitut, Hörsaal | A central goal of current research is to efficiently create entangled states among an increasing number of qubits. While atomic platforms provide great scalability, they mostly rely on local interactions, for instance, collisional or Rydberg interactions. We describe the progress to build a novel platform to entangle atoms with non-local operations using photon-mediated interactions. The atoms will be trapped within individual optical tweezers which are coupled to the field of an optical cavity. Large optical access through a high-resolution microscope objective will enable us to individually address each atom and control its coupling with all-to-all connectivity. Furth! er advant ages of this platform include partial non-destructive readout and efficient multi-qubit entanglement operations. In the long term, the proposed platform provides a scalable path to studying many-body systems with programmable connectivity, as well as an efficient atom-photon interface for quantum communication applications. | Julian Leonard |

16 | Tests of local realism and macrorealism | Johannes Kofler | 7.2.2023 | Johannes Kepler Universität Linz | Local realism is the worldview in which physical properties of objects exist independently of measurement and where physical influences cannot travel faster than the speed of light. Bell’s theorem states that this worldview is incompatible with the predictions of quantum mechanics, as is expressed in Bell’s inequalities. Experimental violations of Bell inequalities are in general vulnerable to so-called “loopholes.” A loophole-free Bell test, closing all major loopholes – the localit! y, freedo m-of-choice, fair-sampling, coincidence-time, and memory loopholes – simultaneously in a single experiment, has been an outstanding goal in the quantum foundations community for many years, even decades. In this talk, I will present our 2015 experiment that closed all major loopholes simultaneously, using a well-optimized source of entangled photons, rapid setting generation, and highly efficient superconducting detectors [1]. In particular, I will discuss the procedure to compute the statistical significance with which we were able to reject local realism by the observed data [2]. Tests of local realism and macrorealism have historically been discussed in very similar terms: Leggett-Garg inequalities follow Bell inequalities as necessary conditions for classical behavior. In the second part of this talk, I compare the probability polytopes spanned by all measurable probability distributions for both scenarios and show that their structure differs strongly between spatially and temporally separated measurements. We arrive at the conclusion that, in contrast to tests of local realism where Bell inequalities form a necessary and sufficient set of conditions, no set of inequalities can ever be necessary and sufficient for a macrorealistic description. Fine’s famous proof that Bell inequalities are necessary and sufficient for the existence of a local realistic model, therefore cannot be transferred to macrorealism. A recently proposed condition, no-signaling in time [3], fulfills this criterion, and we show why it is better suited for future experimenta! l tests a nd theoretical studies of macrorealism. Our work thereby identifies a major difference between the mathematical structures of local realism and macrorealism [4]. [1] M. Giustina, M. A. M. Versteegh, S. Wengerowsky, J. Handsteiner, A. Hochrainer, K. Phelan, F. Steinlechner, J. Kofler, J.- Å. Larsson, C. Abellán, W. Amaya, V. Pruneri, M. W. Mitchell, J. Beyer, T. Gerrits, A. E. Lita, L. K. Shalm, S. W. Nam, T. Scheidl, R. Ursin, B. Wittmann, and A. Zeilinger, Phys. Rev. Lett. 115, 250401 (2015) [2] J. Kofler, M. Giustina, J.-Å. Larsson, and M. W. Mitchell, Phys. Rev. A 93, 032115 (2016) [3] J. Kofler and Č. Brukner, Phys. Rev. A 87, 052115 (2013) [4] L. Clemente and J. Kofler, Phys. Rev. Lett. 116, 150401 (2016) | Armando Rastelli |

17 | Blackbody Radiation Induced Effects and Phenomena | various | 13.-17.2.2023 | ESI Boltzmann Lecture Hall, University of Vienna | Planck's description of blackbody radiation and Einstein's quantum theory of light are arguably the historic foundation of quantum optics. Later, the development of the laser allowed for the coherent control of atoms, which is the basis of today's success of the field. The "optics" part of quantum optics therefore evolved from incoherent, broadband thermal radiation to ultra-stable and narrow-bandwidth lasers. However, the ever growing precision of quantum optics experiments is sparking new interest in describing and understanding how matter interacts with blackbody radiation. This workshop will bring together experimentalists and theoreticians whose research is concerned with, or affected by the interaction of matter with thermal or other broadband radiation. For some, this radiation is a source of noise in their experiments (e.g. for atomic clocks or atom interferometers). Other results demonstrate that broadband radiation induces novel forces and effective interactions of matter. At the workshop we will discuss these and related topics to explore new opportunities and challenges in physics, astrophysics and cosmology. A general outline of the topics covered by the workshop will be given by invited speakers (abstract submission via the online form on this website until January 16th 2023). Additionally, we encourage application for posters by sending a title and a short (one paragraph) abstract to bbriep.workshop@gmail.com until January 16th 2023 (non-registered applicants please include their affiliation, contact details and specify whether they want to apply for financial support or cover their participation fully from own funds). The workshop is financially supported by the Cluster of Excellence QuantumFrontiers - Light and Matter at the Quantum Frontier https://www.quantumfrontiers.de/en/ | Philipp Haslinger (TU Vienna) Francesco Intravaia (HU Berlin) Arkadiusz Kosior (U of Innsbruck) Dennis Rätzel (ZARM, Bremen) |

18 | 1st Symposium on Correlated Quantum Materials & Solid State Quantum Systems | Assaad, F. F.; Belzig, W.; Brinkman, A.; Felser, C.; Higginbotham, A. P.; Huber, M.; Katsaros, G.; Modic, K.; Pixley, J. H.; Scheer, E.; Serbyn, M. | 22.02.2023 | TU Wien, TUtheSky, Getreidemarkt 9 | Dear Colleague! It is our pleasure to invite you to attend this symposium, which is the kickoff event of the SFB project Correlated Quantum Materials & Solid State Quantum Systems (Q-M&S) https://www.fwf.ac.at/de/wissenschaft-konkret/im-fokus-schwerpunkte/f-86-silke-buehler-paschen (the official website https://q-ms.org will be active soon), and will be held as a hybrid event. Please join us online via the Zoom invitation link in the symposium program (see table headers on page 4 and 5), which you can download here: https://owncloud.tuwien.ac.at/index.php/s/eez6b2ckEBBzlLU Should you wish to participate in person, we kindly ask you to register by emailing angelika.bosak@tuwien.ac.at by Friday, 17.02.2023, indicating also which day(s) you wish to attend. We are looking forward to welcoming you at the symposium! Kind regards, Angelika Bosak on behalf of Prof. Dr. Silke Buehler-Paschen Chair 1st Symposium on Correlated Quantum Materials & Solid State Quantum Systems Coordinator SFB Correlated Quantum Materials & Solid State Quantum Systems (Q-M&S) Institute of Solid State Physics - Quantum Materials, TU Wien Wiedner Hauptstr. 8-10/138, 1040 Vienna, Austria and all SFB PIs | Silke Buehler-Paschen, Symposium Chair and Coordinator SFB Q-M&S |

19 | Alpichshev, Z.; Barisic, N.; Gibert, M.; Held, K.; Paschen, S.; Schuch, N.; Walther, P. | 23.2.2023 | TU Wien; Kontaktraum, Gußhausstraße 25-29 | |||

20 | Driven-dissipative crystals of matter and light - from topological pumps to metastable structures | Tobias Donner (Institute for Quantum Electronics, ETH Zurich, Switzerland) | 2.3.2023 | Ernst-Mach Lecture Hall, Boltzmanngasse 5 | Exposing a many-body system to external drives and losses can fundamentally transform the nature of its phases, and opens perspectives for engineering new properties of matter. How such characteristics are related to the underlying microscopic processes is a central question for our understanding of materials. A versatile platform to address it are quantum gases coupled to the dynamic light fields inside optical resonators. This setting allows to create synthetic many-body systems with cavity-mediated long-range atom-atom interactions. If these are sufficiently strong, the system undergoes a structural phase transition to a crystal of matter and light. By engineering the involved light field modes, we study in real-time the dynamics of a first-order phase transition between two such superradiant crystals. When the dissipation via cavity losses and the coherent timescales are comparable, we find a regime of limit cycle oscillations leading to a topological pumping of the atoms. Furthermore, I will report on the exploration of metastable sub- and superradiant atomic structures with lifetimes exceeding any characteristic time scale of the system. | Uros Delic |

21 | Cold atoms from quantum optimization to the simulation of holographic duality | Philipp Hauke (University of Toronto) | 3.3.2023 | Atominstitut, Hörsaal | We are in an era where the pristine level of control over cold atoms and similar platforms is opening unprecedented possibilities to design and probe strongly-correlated many-body systems. In this talk, I want to showcase a few recent developments on the theory side.
First, I will discuss recent advances towards simulating the Sachdev-Ye-Kitaev (SYK) model. Initially introduced as a prototype of strange metals, this model displays a large variety of intriguing phenomena ranging from maximal scrambling to emergent conformal symmetry and holographic duality to black holes. However, a laboratory realization of this rich physics comes with the major challenge of implementing infinite-ranged interactions that are random and uncorrelated. I will highlight some of theory explorations that we have done on that model [1] and explain a proposal for a scalable implementation in a cloud of fermionic atoms trapped in a multi-mode optical cavity. As a preliminary step towards this direction, I will also discuss a recent realization of a disordered Lipkin-Meshkov-Glick model using atoms in a cavity [2]. Moreover, I will put the realization of disordered many-body models into context of quantum optimization, wherein hard optimization problems are rephrased as the task of finding the ground state of a spin glass. In particular, I will discuss the role of entanglement therein and illustrate how the fields of cold-atom quantum metrology and quantum optimization can learn from each other. | Julian Leonard |

22 | Andrew Niels Kanagin (TU Wien) | 8.3.2023 | Atominstitut, Hörsaal | Here I present a novel platform for quantum technologies, where we grow crystals of solid noble gasses (p-H2, Ne, Ar…) which host an ensemble of alkali impurities (Rb, Na, Cs…) at high densities atop a superconducting resonator. The noble gas crystal offers an inert, soft, and versatile matrix which aims to minimize the interaction between the matrix and impurity in hopes to preserve the favorable atomic properties. Additionally, these crystals offer a modular platform for a wide range of impurities to be embedded and studied. The alkali impurities have hyperfine transitions of roughly 1-10GHz, which are coupled to superconducting microwave resonators at temperatures of 50mK. Leveraging the high densities of the alkali impurities, in particular sodium in a solid neon matrix, we achieved strong coupling between the resonator and the ensemble via the collective enhancement coupling factor known from the Tavis-Cummings Hamiltonian. Moreover, I will describe details about the experiment and possible future goals. | RugWay Wu | |

23 | Can we prove that cosmic structures are of quantum mechanical origin? | Vincent Vennin (APC Paris) | 10.3.2023 | Atominstitut, Hörsaal | In the early universe, quantum vacuum fluctuations are amplified and stretched to large distances, giving rise to cosmological over-densities that seed the large-scale structure of our universe. However, astronomers usually analyse the data with purely classical techniques and apparently never need to rely on the quantum formalism to understand them. So are there observational signatures of the quantum origins of primordial perturbations? If confirmed, what would we learn about quantum physics in gravitational contexts? | |

24 | Quantum measurements and equilibration: modelling the emergence of objectivity via entropy maximisation | Maximilian Lock | 15.3.2023 | Atominstitut, Hörsaal | Textbook quantum physics features two types of dynamics: reversible unitary dynamics and irreversible measurements. The latter stands in conflict with the laws of thermodynamics and has evoked much debate. With the help of modern quantum statistical mechanics, we take the first step in formalising the hypothesis that quantum measurements are instead driven by the natural tendency of closed systems to maximise entropy, a notion that we call the Measurement-Equilibration Hypothesis. In this paradigm, we investigate how objective measurement outcomes can emerge within an purely unitary framework, and find that: (i) the interactions used in standard measurement models fail to spontaneously feature emergent objectivity and (ii) while ideal projective measurements are impossible, we can (for a given form of interaction) approximate them exponentially well as we collect more physical systems together into an "observer system". We thus lay the groundwork for self-contained models of quantum measurement, and conclude by proposing some improvements to our simple scheme. | Maximilian Prüfer |

25 | Landau's Fermi liquids with hidden quasiparticles | Prof. Michele Fabrizio (Scuola Internazionale Superiore di Studi Avanzati di Trieste) | 16.3.2023 | TU Wien, Freihaus Hörsaal 3 | Landau’s Fermi liquids, paradigm of interacting electrons, are characterized by the existence of single-particle excitations, the ‘quasiparticles’, with well-defined energy dispersion in momentum space and whose lifetime grows to infinity approaching the quasiparticle ‘Fermi surface’, i.e., the location in the Brillouin zone of the zeros of the quasiparticle energy measured with respect to the chemical potential. Those quasiparticles fully determine the long-wavelength, low-energy, and low-temperature behavi! or of the interacting system. The traditional microscopic derivation of Landau’s Fermi liquid theory relies on the validity of perturbation theory. In that case, quasiparticles appear as peaks in the spectral function that grow and narrow approaching the quasiparticle ‘Fermi surface’, rigorously defined through the poles in momentum space of the single-particle Green’s function at zero energy and temperature. Therefore, each time quasiparticle peaks are absent in the spectral function, that lack is attributed to a breakdown of Landau’s Fermi liquid theory, and often happens in strongly-correlated materials, most notably, in the pseudo-gap phase of underdoped cuprates. However, many purported non-Fermi liquids missing quasiparticle peaks have physical properties that instead hint at the existence of quasiparticles. The most striking example are quantum oscillations, another fingerprint of quasiparticles, and finite specific heat coefficients in the Kondo insulators SmB6 and YbB12. Here, we show that this Janus-faced behavior can be perfectly reconciled with Landau’s Fermi liquid theory. Specifically, we demonstrate that Landau’s Fermi liquid theory can be microscopically derived even when the single-particle Green’s function at zero energy and temperature has a surface of zeros, the so-called Luttinger surface breaking perturbation theory, instead of the Fermi surface poles. Quasiparticles at the Luttinger surface, invisible in the spectral function, are incompressible, do not contribute to the Drude weight, and yet they yield linear in temperature specific heat and thermal conductivity, Pauli-like magnetic susceptibility and, possibly, quantum oscillations. Therefore, for instance, a Mott insulator with a Luttinger surface realizes a spin-liquid insulator, with the Luttinger surface playing the role of the ‘spinon’ Fermi surface. | Sabine Andergassen |

26 | Quantum devices as a meeting point for thermodynamics and machine learning | Natalia Ares | 17.3.2023 | Atominstitut, Hörsaal | As we miniaturize devices to reach the quantum regime, the need arises to test the laws of thermodynamics in a new realm, in which fluctuations and quantum effects play a very important role. I will discuss how to explore the thermodynamics of semiconductor devices at nanometer scales, and I will explain how we measured the thermodynamic cost of recording the passage of time. Electromechanical devices have great potential to build nanoscale motors. Fully suspended carbon nanotube devices allow us to control mechanical and electronic degrees of freedom with high accuracy. Using these devices we show that the transport of an electron can strongly couple to the nanotube motion. I will discuss how these experiments can be extended to study engines where the gas is one or two electrons and the piston is the movement of the nanotube. These experiments and many others require increased levels of sophistication in quantum device control. The calibration and detailed characterization of these devices are tasks that become impossible as the number and complexity of the quantum devices we use grows. I will show that artificial intelligence algorithms are capable of characterizing and calibrating quantum devices fully automatically and even more efficiently than human experts. | Marcus Huber |

27 | Efficient Control and Characterization of quantum dynamics using calculus: A numerical approach | Priya Batra (IISER Pune) | 21.3.2023 | Institute of Science and Technology Austria (ISTA) | In this talk, I will briefly discuss a few numerical techniques to control and characterize quantum dynamics. Understanding quantum dynamics is a backbone for various quantum technologies and condensed matter systems. In my work, I have developed many techniques, including machine learning to control the system efficiently. We have used a machine learning algorithm called the Recommender system to characterize the dynamics regarding quantum correlations. We have! also use d the same algorithm to expedite the control problem. I hope to give you a brief idea of the field in my talk. | Maksym Serbyn |

28 | Nano-optics with free electrons | Mathieu Kociak (CNRS/Université Paris Saclay, Orsay, France) | 21.04.2023 | Atominstitut, Hörsaal | Semiconductor quantum dots embedded in photonic nanostructures offer a highly efficient and coherent deterministic photon-emitter interface [1,2]. It constitutes an on-demand single-photon Electron spectroscopy using free electrons in electron microscopes (EM) probably entered the field of nano-optics at the end of the 20th century, with among other the pivotal paper of Yamamoto1 showing the mapping of plasmonic modes with deep sub-wavelength resolution. Since then, the field has kept growing exponentially, with applications from plasmons, phonons or exciton mapping at near atomic resolution, to quantum optics of nanomaterials or of the free electrons themselves2. These results have been boosted by constant disruptions in technology – monochromation, fs sources of pulsed electrons, high efficiency light injection and detection system in the EM - and theory – introduction of concepts of optics or nano-optics in the realm of EM, such as EMLDOS or quantum statistics, to name a few. In this talk, I will try to cover some of these results. Given the audience, I will put a little bit more emphasis on few examples where quantum coherence may, or not, play a role. With this in mind, I will first present a rapid overview of recent development in nanooptics with free electron beams. I will then focus on two major issues in the fields. The first one relates to the study of high-quality factor photonic cavities, which are limited by the spectral resolution of common EM techniques. I will show how we can use a new type of spectroscopy that allies the spectral resolution of lasers to the spatial resolution of free electrons to resolve these photonic cavity modes3. The second relates to the relation between the energy transferred from a free electron to a nanomaterial, as detected by electron energy loss spectroscopy (EELS) and the subsequent emission of light (aka cathodoluminescence, CL). The relation between the two events has been for a long time totally elusive. We will see that the coincident measurement of these two signals brings our understanding a step further by unveiling the fate of optical excitations, from their creation through absorption to their annihilation through emission4. References 1. Yamamoto, N., Araya, K. & García de Abajo, F. J. Photon emission from silver particles induced by a high-energy electron beam. Phys. Rev. B - Condens. Matter Mater. Phys. 64, 2054191–2054199 (2001). 2. Polman, A., Kociak, M. & García de Abajo, F. J. Electron-beam spectroscopy for nanophotonics. Nat. Mater. 18, 1158–1171 (2019). 3. Auad, Y. et al. µeV electron spectromicroscopy using free-space light. arXiv:2212.12457 (2022). 4. Varkentina, N. et al. Cathodoluminescence excitation spectroscopy: Nanoscale imaging of excitation pathways. Sci. Adv. 8, (2022). | Philipp Haslinger |

29 | Can we observe non-perturbative vacuum shifts in cavity QED? | Rocio Saez Blazquez (TU Wien) | 26.04.2023 | Atominstitut, Hörsaal | In recent years, vacuum-induced modifications of molecular properties have regained considerable attention in the context of cavity QED, where the coupling of matter to individual electromagnetic modes is strongly enhanced by a tight confinement of the field. It has been speculated that under such ultrastrong coupling conditions, the electromagnetic vacuum could change the rate of chemical reactions or modify work functions, phase transitions and (super-)conductivity, even without externally driving the cavity mode.In this work we investigate the ground state energy shift of a single dipole due to its coupling to the electromagnetic vacuum in a confined geometry and address the fundamental question of whether or not it is possible to achieve conditions under which the light-matter coupling can result in non-perturbative corrections to the dipole’s ground state. To do so we consider two simplified, but otherwise rather generic cavity QED setups, which allow us to derive analytic expressions for the total ground state energy and to distinguish explicitly between purely electrostatic and genuine vacuum-induced contributions. Importantly, this derivation takes the full electromagnetic spectrum into account while avoiding any ambiguities arising from an ad-hoc mode truncation. Our findings show that while the effect of confinement per se is not enough to result in substantial vacuum-induced corrections, the presence of high-impedance modes, such as plasmons or engineered LC resonances, can drastically increase these effects.References 1. Yamamoto, N., Araya, K. & García de Abajo, F. J. Photon emission from silver particles induced by a high-energy electron beam. Phys. Rev. B - Condens. Matter Mater. Phys. 64, 2054191–2054199 (2001). 2. Polman, A., Kociak, M. & García de Abajo, F. J. Electron-beam spectroscopy for nanophotonics. Nat. Mater. 18, 1158–1171 (2019). 3. Auad, Y. et al. µeV electron spectromicroscopy using free-space light. arXiv:2212.12457 (2022). 4. Varkentina, N. et al. Cathodoluminescence excitation spectroscopy: Nanoscale imaging of excitation pathways. Sci. Adv. 8, (2022). | Sebastian Erne |

30 | Phase Encoding for Super-Resolution Magnetic Microscopy with Diamond NV Centers | Shawn Storm (TU München) | 28.04.2023 | Atominstitut, Seminarraum ZA | Over the last two decades, NV centers have gained interest in the life sciences due to their nanoscale sensing and imaging abilities. Real-space imaging techniques with NV centers are either limited by the optical diffraction limit of approximately 400 nm or require cumbersome point-by-point scanning probe techniques for nanoscale resolution. An alternative technique in Fourier imaging from conventional magnetic resonance imaging (MRI) has been shown to go beyond this limit, however, with scanning probe microscopy. This thesis provides a proof of concept of the Fourier imaging technique with widefield microscopy. The design is simulated with the use of COMSOL Multiphysics, and the theoretical spatial resolution is discussed.1. Yamamoto, N., Araya, K. & García de Abajo, F. J. Photon emission from silver particles induced by a high-energy electron beam. Phys. Rev. B - Condens. Matter Mater. Phys. 64, 2054191–2054199 (2001). 2. Polman, A., Kociak, M. & García de Abajo, F. J. Electron-beam spectroscopy for nanophotonics. Nat. Mater. 18, 1158–1171 (2019). 3. Auad, Y. et al. µeV electron spectromicroscopy using free-space light. arXiv:2212.12457 (2022). 4. Varkentina, N. et al. Cathodoluminescence excitation spectroscopy: Nanoscale imaging of excitation pathways. Sci. Adv. 8, (2022). | Julian Leonard |

31 | Dark dimension and a unification of the dark sector | Cumrun Vafa (Harvard University) | 3.5.2023 | Schrödinger Lecture Hall, ESI, Boltzmanngasse 9/2 | In this talk I apply consistency conditions of quantum gravity to the dark sector. Motivated by the smallness of the dark energy combined with other experimental data, one is naturally led to a corner of the quantum gravity landscape with one extra mesoscopic dimension in the micron range. Interestingly this also leads to graviton excitations in the 5th dimension as an unavoidable candidate for the dark matter. Moreover, TCC conjecture applied to the late time cosmology motivates specific initial conditions in this scenario, leading to the right abundance of dark matter gravitons and an explanation of the cosmological coincidence problem. I also explain how the cosmological S8 tension gets resolved. References 1. Yamamoto, N., Araya, K. & García de Abajo, F. J. Photon emission from silver particles induced by a high-energy electron beam. Phys. Rev. B - Condens. Matter Mater. Phys. 64, 2054191–2054199 (2001). 2. Polman, A., Kociak, M. & García de Abajo, F. J. Electron-beam spectroscopy for nanophotonics. Nat. Mater. 18, 1158–1171 (2019). 3. Auad, Y. et al. µeV electron spectromicroscopy using free-space light. arXiv:2212.12457 (2022). 4. Varkentina, N. et al. Cathodoluminescence excitation spectroscopy: Nanoscale imaging of excitation pathways. Sci. Adv. 8, (2022). | Markus Aspelmeyer |

32 | Femtosecond and attosecond electron microscopy: Seeing atoms and electrons in space and time the dark sector | Peter Baum | 3.5.2023 | Univ. Wien, Lise Meitner lecture hall, 1st floor Boltzmanngasse 5, 1090 Vienna | The fundamental reason behind almost any light-matter interaction are atomic and electronic motion in space and time. In order to provide a movie-like access to such dynamics, we unify electron microscopy with attosecond and femtosecond laser technology. In this way, we combine the awesome spatial resolution of modern electron beams with the spectacular time resolution that is offered by the cycle period of light [1-2]. Selected results will be reported on the electric fields within metamaterials [2-3], the Einstein-de-Haas effect on atomic dimensions [4], the reaction path of phase transitions [5] and the formation of free-electron qubit states [6]. Many breakthroughs in science and technology have been achieved by novel imaging techniques, and we will discuss how our ultrafast electron microscopy may contribute. [1] D. Nabben, J. Kuttruff, L. Stolz, A. Ryabov, P. Baum, "Attosecond electron microscopy of sub-cycle optical dynamics“, Nature, accepted (2023). [2] C. Kealhofer, W. Schneider, D. Ehberger, A. Ryabov, F. Krausz, P. Baum, “All-optical control and metrology of electron pulses”, Science 352, 429 (2016). [3] A. Ryabov and P. Baum, “Electron microscopy of electromagnetic waveforms”, Science 353, 374 (2016). [4] S. R. Tauchert, M. Volkov, D. Ehberger, D. Kazenwadel, M. Evers, H. Lange, A. Donges, A. Book, W. Kreuzpaintner, U. Nowak, P. Baum, “Polarized phonons carry angular momentum in femtosecond demagnetization”, Nature 602, 73 (2022). [5] P. Baum, Ding-Shyue Yang, A. H. Zewail, “4D Visualization of Transitional Structures in Phase Transformations by Electron Diffraction”, Science 318, 788 (2007). [6] M. Tsarev, A. Ryabov, P. Baum, “Free-Electron Qubits and Maximum-Contrast Attosecond Pulses via Temporal Talbot Revivals”, Phys. Rev. Res. 3, 043033 (2021). 1. Yamamoto, N., Araya, K. & García de Abajo, F. J. Photon emission from silver particles induced by a high-energy electron beam. Phys. Rev. B - Condens. Matter Mater. Phys. 64, 2054191–2054199 (2001). 2. Polman, A., Kociak, M. & García de Abajo, F. J. Electron-beam spectroscopy for nanophotonics. Nat. Mater. 18, 1158–1171 (2019). 3. Auad, Y. et al. µeV electron spectromicroscopy using free-space light. arXiv:2212.12457 (2022). 4. Varkentina, N. et al. Cathodoluminescence excitation spectroscopy: Nanoscale imaging of excitation pathways. Sci. Adv. 8, (2022). | Thomas Juffmann |

33 | Electron-light coupling in photonic nanostructures: From coherent electron acceleration to a quantum-coherent coupling | Peter Hommelhoff | 3.5.2023 | Univ. Wien, Lise Meitner lecture hall, 1st floor Boltzmanngasse 5, 1090 Vienna | It is well known that electrons and light do not couple efficiently in free space -- but with the introduction of appropriate nanostructures, they do. Based on this, we have built a nanoscale version of a classical RF accelerator, including optical forces to not only accelerate electrons but also collimate them in the 225 nm narrow nanophotonic channel, representing the first demonstration of the accelerator on a chip reaching substantial energy gains. In the second part, I will briefly show how a high-resolution spectrometer inside of a scanning elec! tron micr oscope allowed us to demonstrate that the electron-light coupling works in a quantum-coherent fashion. The talk will give an overview of the nascent yet already vibrant field of efficient free electron-light coupling. [1] D. Nabben, J. Kuttruff, L. Stolz, A. Ryabov, P. Baum, "Attosecond electron microscopy of sub-cycle optical dynamics“, Nature, accepted (2023). [2] C. Kealhofer, W. Schneider, D. Ehberger, A. Ryabov, F. Krausz, P. Baum, “All-optical control and metrology of electron pulses”, Science 352, 429 (2016). [3] A. Ryabov and P. Baum, “Electron microscopy of electromagnetic waveforms”, Science 353, 374 (2016). [4] S. R. Tauchert, M. Volkov, D. Ehberger, D. Kazenwadel, M. Evers, H. Lange, A. Donges, A. Book, W. Kreuzpaintner, U. Nowak, P. Baum, “Polarized phonons carry angular momentum in femtosecond demagnetization”, Nature 602, 73 (2022). [5] P. Baum, Ding-Shyue Yang, A. H. Zewail, “4D Visualization of Transitional Structures in Phase Transformations by Electron Diffraction”, Science 318, 788 (2007). [6] M. Tsarev, A. Ryabov, P. Baum, “Free-Electron Qubits and Maximum-Contrast Attosecond Pulses via Temporal Talbot Revivals”, Phys. Rev. Res. 3, 043033 (2021). 1. Yamamoto, N., Araya, K. & García de Abajo, F. J. Photon emission from silver particles induced by a high-energy electron beam. Phys. Rev. B - Condens. Matter Mater. Phys. 64, 2054191–2054199 (2001). 2. Polman, A., Kociak, M. & García de Abajo, F. J. Electron-beam spectroscopy for nanophotonics. Nat. Mater. 18, 1158–1171 (2019). 3. Auad, Y. et al. µeV electron spectromicroscopy using free-space light. arXiv:2212.12457 (2022). 4. Varkentina, N. et al. Cathodoluminescence excitation spectroscopy: Nanoscale imaging of excitation pathways. Sci. Adv. 8, (2022). | Thomas Juffmann |

34 | Towards an Artificial Muse for new ideas in Physics | Mario Krenn | 4.5.2023 | Max Perutz Labs, Dep. for Structural Biology, Campus Vienna Biocenter 5, 1030 Wien | Artificial intelligence (AI) is a potentially disruptive tool for physics and science in general. One crucial question is how this technology can contribute at a conceptual level to help acquire new scientific understanding or inspire new surprising ideas. I will talk about how AI can be used as an artificial muse in quantum physics, which suggests surprising and unconventional ideas and techniques that the human scientist can interpret, understand and generalize to its fullest potential. [1] Krenn, Kottmann, Tischler, Aspuru-Guzik, Conceptual understanding through efficient automated design of quantum optical experiments. Physical Review X 11(3), 031044 (2021). [2] Krenn, Pollice, Guo, Aldeghi, Cervera-Lierta, Friederich, Gomes, Häse, Jinich, Nigam, Yao, Aspuru-Guzik, On scientific understanding with artificial intelligence. Nature Reviews Physics 4, 761–769 (2022). [3] Krenn, Zeilinger, Predicting research trends with semantic and neural networks with an application in quantum physics. PNAS 117(4), 1910-1916 (2020). [2] C. Kealhofer, W. Schneider, D. Ehberger, A. Ryabov, F. Krausz, P. Baum, “All-optical control and metrology of electron pulses”, Science 352, 429 (2016). [3] A. Ryabov and P. Baum, “Electron microscopy of electromagnetic waveforms”, Science 353, 374 (2016). [4] S. R. Tauchert, M. Volkov, D. Ehberger, D. Kazenwadel, M. Evers, H. Lange, A. Donges, A. Book, W. Kreuzpaintner, U. Nowak, P. Baum, “Polarized phonons carry angular momentum in femtosecond demagnetization”, Nature 602, 73 (2022). [5] P. Baum, Ding-Shyue Yang, A. H. Zewail, “4D Visualization of Transitional Structures in Phase Transformations by Electron Diffraction”, Science 318, 788 (2007). [6] M. Tsarev, A. Ryabov, P. Baum, “Free-Electron Qubits and Maximum-Contrast Attosecond Pulses via Temporal Talbot Revivals”, Phys. Rev. Res. 3, 043033 (2021). 1. Yamamoto, N., Araya, K. & García de Abajo, F. J. Photon emission from silver particles induced by a high-energy electron beam. Phys. Rev. B - Condens. Matter Mater. Phys. 64, 2054191–2054199 (2001). 2. Polman, A., Kociak, M. & García de Abajo, F. J. Electron-beam spectroscopy for nanophotonics. Nat. Mater. 18, 1158–1171 (2019). 3. Auad, Y. et al. µeV electron spectromicroscopy using free-space light. arXiv:2212.12457 (2022). 4. Varkentina, N. et al. Cathodoluminescence excitation spectroscopy: Nanoscale imaging of excitation pathways. Sci. Adv. 8, (2022). | Thomas Juffmann |

35 | Engineering exotic superfluids with optically-dressed Bose-Einstein condensates | Letizia Tarruell (ICFO Barcelona) | 5.5.2023 | Atominstitut, Helmut Rauch Lecture Hall | Spin-orbit coupled Bose-Einstein condensates, where the internal state of the atoms is linked to their momentum through optical coupling, are a flexible experimental platform to engineer synthetic quantum many-body systems. In my talk, I will present recent work where we have exploited the interplay of spin-orbit coupling and tunable interactions in potassium BECs to realize two unconventional superfluid phases. In a first series of experiments, we optically couple two internal states of 39K with very unequal scattering lengths using two-photon Raman transitions. This results in a BEC where the interactions are effectively chiral, i.e. depend on the propagation direction of the atoms. We show that under appropriate conditions the Hamiltonian of the system corresponds to the chiral BF theory: a one-dimensional reduction of the celebrated Chern-Simons gauge that effectively describes fractional quantum Hall states [1]. Our chiral BECs allow us to reveal the key properties of the chiral BF theory: the formation of chiral solitons and the emergence of an electric field generated by the system itself [2]. Our results thus expand the scope of quantum simulation to topological gauge theories and open a route to implement analogous theories in higher dimensions. In a second series of experiments, we address instead the regime of weak optical coupling, where the dispersion relation of the atoms acquires a characteristic double-well structure. When the intrawell interactions dominate over the interwell ones, both minima are occupied and their populations interfere, leading to a system with a modulated (striped) density profile. The BEC then behaves as a supersolid: a phase that spontaneously breaks both gauge and translation symmetry, and which combines the frictionless flow of a superfluid and the crystalline structure of a solid. We realize this situation in a spin-orbit coupled 41K, where the difference of intraspin and interspin scattering lengths results in a stable supersolid stripe phase over a broad range of Raman coupling parameters. Using a matter-wave lensing technique, we magnify the density profile of the cloud and measure in situ the contrast and spacing of the stripes. Our experiments visualize the crystalline nature of the supersolid stripe phase, and provide an excellent starting point to investigate its excitations. [1] C. S. Chisholm, A. Frölian, E. Neri, R. Ramos, L. Tarruell, and A. Celi Encoding a one-dimensional topological gauge theory in a Raman-coupled Bose-Einstein condensate Phys. Rev. Research 4, 043088 (2022) [2] A. Frölian, C. S. Chisholm, E. Neri, C. R. Cabrera, R. Ramos, A. Celi, and L. Tarruell Realizing a 1D topological gauge theory in an optically dressed BEC Nature 608, 293–297 (2022) [1] Krenn, Kottmann, Tischler, Aspuru-Guzik, Conceptual understanding through efficient automated design of quantum optical experiments. Physical Review X 11(3), 031044 (2021). [2] Krenn, Pollice, Guo, Aldeghi, Cervera-Lierta, Friederich, Gomes, Häse, Jinich, Nigam, Yao, Aspuru-Guzik, On scientific understanding with artificial intelligence. Nature Reviews Physics 4, 761–769 (2022). [3] Krenn, Zeilinger, Predicting research trends with semantic and neural networks with an application in quantum physics. PNAS 117(4), 1910-1916 (2020). [2] C. Kealhofer, W. Schneider, D. Ehberger, A. Ryabov, F. Krausz, P. Baum, “All-optical control and metrology of electron pulses”, Science 352, 429 (2016). [3] A. Ryabov and P. Baum, “Electron microscopy of electromagnetic waveforms”, Science 353, 374 (2016). [4] S. R. Tauchert, M. Volkov, D. Ehberger, D. Kazenwadel, M. Evers, H. Lange, A. Donges, A. Book, W. Kreuzpaintner, U. Nowak, P. Baum, “Polarized phonons carry angular momentum in femtosecond demagnetization”, Nature 602, 73 (2022). [5] P. Baum, Ding-Shyue Yang, A. H. Zewail, “4D Visualization of Transitional Structures in Phase Transformations by Electron Diffraction”, Science 318, 788 (2007). [6] M. Tsarev, A. Ryabov, P. Baum, “Free-Electron Qubits and Maximum-Contrast Attosecond Pulses via Temporal Talbot Revivals”, Phys. Rev. Res. 3, 043033 (2021). 1. Yamamoto, N., Araya, K. & García de Abajo, F. J. Photon emission from silver particles induced by a high-energy electron beam. Phys. Rev. B - Condens. Matter Mater. Phys. 64, 2054191–2054199 (2001). 2. Polman, A., Kociak, M. & García de Abajo, F. J. Electron-beam spectroscopy for nanophotonics. Nat. Mater. 18, 1158–1171 (2019). 3. Auad, Y. et al. µeV electron spectromicroscopy using free-space light. arXiv:2212.12457 (2022). 4. Varkentina, N. et al. Cathodoluminescence excitation spectroscopy: Nanoscale imaging of excitation pathways. Sci. Adv. 8, (2022). | Julian Leonard |

36 | Sculpted light nano and microsystems | Halina Rubinsztein-Dunlop (The University of Queensland, Australia) | 11.5.2023 | Atominstitut, Helmut Rauch Lecture Hall | Sculpted light refers to the generation of custom designed light fields. These light fields can be applied in many diverse fields ranging from interrogating single atoms or atom assembly to using these fields for optical micromanipulation and optical tweezers as well as creating new quantum devices and sensors. We consider here the study and application of light with structured intensity, polarization and phase. We can create custom fields in multiple planes using dynamic and geometric phase control. Sculpted light can be generated using spatial light modulators (SLM) or digital micromirror devices (DMD) and enable the production of configurable and flexible confining potentials at the nano and micron-scale. This results in production of highly configurable time-averaged traps. All these methods achieve dynamical and flexible sculpted light fields and enable imaging of the amplitude patterns, phase and polarization. These sculpted light fields can be used for intricate studies of light -matter interactions in a variety of environments. I will describe their applications to trapping and manipulating nano and micron-size objects with examples ranging from atomtronics to measurements in-vivo inside biological cells and for studies of active matter. | Jörg Schmiedmayer |

37 | Quantum Gas in a box | Zoran Hadzibabic (University of Cambridge) | 12.5.2023 | Atominstitut, Helmut Rauch Lecture Hall | For nearly three decades ultracold atomic gases have been used with great success to study fundamental many-body phenomena such as Bose-Einstein condensation and superfluidity. While traditionally they were produced in harmonic electromagnetic traps and thus had inhomogeneous densities, it is now also possible to create homogeneous samples in the uniform potential of an optical box trap [1]. Box trapping simplifies the interpretation of experimental results, provides more direct connections with theory and, in some cases, allows qualitatively new, hitherto impossible experiments. I will give an overview of our recent experiments with box-trapped three- and two-dimensional Bose gases, focusing on a series of related experiments on far-from-equilibrium phenomena, including turbulence [2-4] and dynamic scaling in driven disordered gases [5]. [1] Quantum gases in optical boxes (review), N. Navon, R. P. Smith, and Z. Hadzibabic, Nat. Phys. 17, 1334 (2021). [2] Emergence of a turbulent cascade in a quantum gas, N. Navon, A. L. Gaunt, R. P. Smith, and Z. Hadzibabic, Nature 539, 72 (2016). [3] Emergence of isotropy and dynamic scaling in 2D wave turbulence in a homogeneous Bose gas, M. Galka et al., Phys. Rev. Lett. 129, 190402 (2022). [4] Universal equation of state for wave turbulence in a quantum gas, L. H. Dogra et al., arXiv:2212.08652 [5] Observation of subdiffusive dynamic scaling in a driven and disordered box-trapped Bose gas, G. Martirosyan et al., arXiv:2304.06697 | Jörg Schmiedmayer |

38 | From Superconducting Circuits to Topological Insulator Floquet Modes: Singal Amplification and Generating Entanglement | Seyed Shabir Barzanjeh (University of Calgary | CA) | 16.5.2023 | Heinzel Seminarraum, ISTA | Seyed Shabir Barzanjeh (University of Calgary | CA) | Johannes Fink |

39 | “Quantum Biology”: how nature harnesses quantum processes to function optimally, and how might we control such quantum processes to therapeutic and tech advantage | Clarice D. Aiello (University of California, Los Angeles) | 6.10.2023 | Atominstitut, Helmut Rauch Lecture Hall | Imagine driving cell activities to treat injuries and disease simply by using tailored magnetic fields. Many relevant physiological processes, such as: the regulation of oxidative stress, proliferation, and respiration rates in cells; wound healing; ion channel functioning; and DNA repair were all demonstrated to be controlled by weak magnetic fields (with a strength on the order of that produced by your cell phone). Such macroscopic physiological responses to magnetic fields are consistent with being driven by chemical reactions that depend on the electron quantum property of spin. In the long-term, the electromagnetic fine-tuning of endogenous “quantum knobs” existing in nature could enable the development of drugs and therapeutic devices that could heal the human body — in a way that is non-invasive, remotely actuated, and easily accessible by anyone with a mobile phone. However, whereas spin-dependent chemical reactions have been unambiguously established for test-tube chemistry (bearing uncanny similarities with what physicists call “spin quantum sensing”), current research has not been able to deterministically link spin states to physiological outcomes in vivo and in real time. With novel quantum instrumentation, we are learning to control spin states within cells and tissues, having as a goal to write the “codebook” on how to deterministically alter physiology with weak magnetic fields to therapeutic and technological advantage. Bio Prof. Clarice D. Aiello is a quantum engineer interested in how quantum physics informs biology at the nanoscale. She is an expert on nanosensors harnessing room-temperature quantum effects in noisy environments. Aiello received her B.S. in Physics from the Ecole Polytechnique; her M.Phil. in Physics from the University of Cambridge, Trinity College; and her Ph.D. from MIT in Electrical Engineering. She also held postdoctoral appointments in Bioengineering at Stanford, and in Chemistry at Berkeley. Two months before the pandemic, she joined UCLA, where she leads the Quantum Biology Tech (QuBiT) Lab. | Amin Tajik |

40 | Error-robust implementations of Quantum Signal Processing using Rydberg atoms | Sina Zeytinoglu , NTT Research (Japan) | 10.10.2023 | Atominstitut, Helmut Rauch Lecture Hall | Reducing the errors induced by gate implementations is crucial for building reliable quantum computers out of externally controlled quantum devices. An experimentalist attempting to control a microscopic quantum mechanical device harnesses the interactions between the device and its environment, an act that inevitably induces errors. Hence, an overarching goal of quantum control theory has been developing error-robust control protocols that leverage the structure of small-scale quantum systems to reduce gate-induced errors. However, until recently, employing a similar strategy for large-scale quantum systems was infeasible because of a lack of known general structures describing quantum algorithms, let alone those that can be leveraged for error-robust implementations. Here, we design error-robust implementations of a broad range of quantum algorithms by studying the structures unveiled by a recently developed iterative compilation method called Quantum Signal Processing (QSP) [2]. We observe that the gate-induced error probability associated with a QSP protocol depends strongly on the error characteristics of single controlled unitary operations. In particular, we show that if controlled unitary gates are perfectly error-biased (i.e., they induce errors only when the control register occupies a certain bitstring), then each QSP iterate can be implemented with only constant error probability. Through numerical simulations, we demonstrate that an experimentally feasible Rydberg atom implementation of controlled unitary gates [3] can achieve an error bias of more than a hundredfold. Our results indicate that gate-induced error probability, rather than the number of gates, is the fundamental metric for evaluating the performance of quantum protocols. [1] S. Zeytinoglu. , S. Sugiura, Error-Robust Quantum Signal Processing using Rydberg Atoms arXiv:2201.04665 [2] G.H. Low, I. Chuang, Optimal Hamiltonian Simulation by Quantum Signal Processing, Phys. Rev. Lett. 118, 010501 (2017) [3] M. Müller, I. Lesanovsky, H. Weimer, H.P. Bühler, and P. Zoller, Mesoscopic Rydberg Gate based on Electromagnetically Induced Transparency, Phys. Rev. Lett. 102, 170502 (2009) | Paul Erker |

41 | Experimental tests of Bell’s inequalities at Institut d’Optique (1980-82): past achievements and future directions | Philippe Grangier (Institut d’Optique Graduate School, CNRS, Université Paris-Saclay | 6.11.2023 | Lise Meitner Lecture Hall, University of Vienna | We will review the motivations and history of the experiments that lead to the Nobel Prize in Physics 2022, attributed to Alain Aspect, John Clauser and Anton Zeilinger. We will then discuss some future perpectives, both on the side of quantum technologies, and on the side of the more philosophical issues that motivated initially these experiments. | Anton Zeilinger, Borivoje Dakic |

42 | Quantum many body physics far from equilibrium from a Quantum Information point of view: Measurement induced dynamics and its breakdown via a spin-glass transition | Yuri Minoguchi (TU Wien) | 8.11.2023 | Atominstitut, Helmut Rauch Lecture Hall | Quantum (and even classical) many body physics far from equilibrium is still a widely uncharted territory with no immediate hope for a deep underlying principle as is available in equilibrium. In a quest for a better understanding of many body dynamics, condensed matter physicists turned to quantum information. There it is common practice to classify the physics according to whether they constitute a resource to accomplish a “useful" task. Recently this program was applied to classify the dynamics of many body systems. The question there is whether some time evolution is good at hiding information from an eavesdropping third party’s measurements i.e. a good quantum errror correcting code. This line of research has become wildly popular and is sometimes also referred to by as “measurement induced dynamics”. In this talk we present our recent results on the extending this program from one eavesdropper to the experimentally more relevant situation of many eavesdroppers, also known as a “bath". We find that these situations are separated by a sharp transition which we characterize by a mapping to the statistical mechanics of a spin-glass which we solve using a replica field theory. This talk is meant to be self contained and to include scientist from all backgrounds at ATI so I will make an effort to explain all scary sounding terms like “quantum error correction”, “spin-glass” and “replica field theory”. | Maximilian Prüfer |

43 | Quantum Systems under Drive: From Micro- to Macrophysics | Sebastian Diehl (Universität Köln) | 10.11.2023 | Atominstitut, Helmut Rauch Lecture Hall | Recent developments in diverse areas - ranging from cold atomic gases over light-driven semiconductors to microcavity arrays - move systems into the focus, which are located on the interface of quantum optics, many-body physics and statistical mechanics. These driven open quantum systems share in common that coherent and driven-dissipative quantum dynamics occur on an equal footing, placing them far away from thermodynamic equilibrium. We will highlight two phenomena, which witness the microscopic breaking of equilibrium conditions on a macroscopic scale, and thus do not have immediate counterparts in equilibrium many-body physics. First, we investigate the fate of the famous Kosterlitz-Thouless phase transition — a topological phase transition in two dimensions — under driving conditions. We show that an infinitesimal non-equilibrium perturbation is sufficient to suppress this transition in large systems. On the other hand, we point out a new intrinsic non-equilibrium phase transition characterized by the onset of deterministic chaos. Second, we argue that drive and dissipation need not to act destructively on fragile quantum mechanical correlations such as phase coherence, entanglement or topological order, but on the contrary the latter can be even created by suitably combing the former to a new dynamical resource. | Julian Leonard |

44 | New platforms for quantum sensing and quantum computing | Nathalie P. de Leon, Department of Electrical and Computer Engineering (Princeton University) | 17.11.2023 | Atominstitut, Helmut Rauch Lecture Hall | The nitrogen vacancy (NV) center in diamond exhibits spin-dependent fluorescence and long spin coherence times under ambient conditions, enabling applications in quantum information processing and sensing. NV centers near the surface can have strong interactions with external materials and spins, enabling new forms of nanoscale spectroscopy. However, NV spin coherence degrades within 100 nanometers of the surface, suggesting that diamond surfaces are plagued with ubiquitous defects. I will describe our recent efforts to correlate direct materials characterization with single spin measurements to devise methods to stabilize highly coherent NV centers within nanometers of the surface. We deploy these coherent shallow NV centers for a new nanoscale sensing technique, whereby we use covariance measurements of two or more NV centers to measure two-point magnetic field correlators. Our approach for correlating surface spectroscopy techniques with single qubit measurements to realize directed improvements is generally applicable to many systems. Separately, I will describe our recent efforts to tackle noise and microwave losses in superconducting qubits. Building large, useful quantum systems based on transmon qubits will require significant improvements in qubit relaxation and coherence times, which are orders of magnitude shorter than limits imposed by bulk properties of the constituent materials. This indicates that loss likely originates from uncontrolled surfaces, interfaces, and contaminants. Previous efforts to improve qubit lifetimes have focused primarily on designs that minimize contributions from surfaces. However, significant improvements in the lifetime of planar transmon qubits have remained elusive for several years. We have recently fabricated planar transmon qubits that have both lifetimes and coherence times exceeding 0.3 milliseconds by using tantalum as the material in the capacitor. Following this discovery, we have parametrized the remaining sources of loss in state-of-the-art devices using systematic measurements of the dependence of loss on temperature, power, and geometry. This parametrization, complemented by direct materials characterization, allows for rational, directed improvement of superconducting qubits. | Andrew Kanagin |

45 | Fiber Fabry-Pérot Fabrication for Enhanced Atom-Cavity Coupling | Isabelle Safa (TU wien) | 22.11.2023 | Atominstitut, Helmut Rauch Lecture Hall | Cold atoms are a leading platform for quantum computation thanks to their coherence properties, microscopic controllability, and scalability. While current quantum processors with neutral atoms are limited to local interactions, our experiment aims to reach programmable and large scale connectivity between Rubidium atoms by means of optical cavity-generated interactions. For this purpose, a small yet open cavity with compact mode geometry is required. Suitable devices are thereupon fiber Fabry-Pérot cavities (FFPC), the mirrors of which are directly machined on the end facets of two face-to-face optical fibers. These micrometer-scale, concave mirrors thus form a miniaturized Fabry-Pérot interferometer. In this talk, I will present the work done during my master thesis at the ATI in the group of Julian Léonard, in which I started to build a setup for this micro-mirror machining. The process consists of three main steps : the glass ablation on the fiber end facet with a CO2 laser, the imaging of the machined fiber by interferometry, and the numerical reconstruction of the mirror surface. | Julian Leonard |