22. November 2021

Gemma de la Cuevas (Universität Innsbruck)

From simplicity to universality and undecidability

29. November 2021

Monika Aidelsburger (LMU Munich)

Quantum simulation with ultracold atoms – from Hubbard models to gauge theories

Well-controlled synthetic quantum systems, such as ultracold atoms in optical
lattices, offer intriguing possibilities to study complex many-body problems in
regimes that are beyond reach using state-of-the-art numerical techniques. This
enables us, for instance, to shed new light on fundamental questions about the
thermalization of isolated quantum many-body systems. Recently, a class of models
has been identified that lies in between the extreme limits of thermal and localizing
behavior. Here ergodicity-breaking occurs due to an emergent fragmentation of the
many-body Hilbert space. A versatile platform that paves the way towards studying
these phenomena is the 1D Fermi-Hubbard model with a strong linear potential.
During the last years the range of accessible condensed matter model Hamiltonians
has been extended towards topological systems. One important ingredient was the
realization of artificial gauge fields via the technique of periodic driving, also known
as Floquet engineering, which further allows the realization of genuine out-ofequilibrium
topological phases that do not have any static counterpart. The success
of Floquet engineering triggered new efforts among experimentalists to build on this
vast toolbox and realize non-trivial matter-gauge couplings – a central ingredient for
the simulation of so-called lattice gauge theories (LGTs). LGTs play a fundamental
role in a variety of areas including high-energy physics and topological quantum
computation. So far successful experimental implementations, however, were limited
to small building blocks of few sites due to the complex local structure of the theory.
We are currently developing a new scheme based on correlated tunneling of
fermionic atoms and local state-dependent control using optical tweezers to realize a
scalable platform for the simulation of U(1) LGTs, relevant for quantum
electrodynamics.

6. December 2021

Miguel Navascués (Austrian Academy of Sciences - IQOQI)

The world is not real

Although most theories of physics are based on real numbers, quantum theory was the first to be formulated in terms of operators acting on complex Hilbert spaces. This has puzzled countless physicists, including the fathers of the theory, for whom a real version of quantum theory, with real operators and states, seemed much more natural. In fact, previous works showed that such a "real quantum theory" can reproduce the outcomes of any multipartite experiment, as long as the parts share arbitrary real quantum states. In this talk I will show that real and complex quantum theory make different predictions in network scenarios comprising independent states and measurements. This allows us to devise a Bell-like experiment whose successful realization would disprove real quantum theory, just as standard Bell experiments disproved classical physics.

13. December 2021

Norbert Schuch (University of Vienna)

Quantum Information and Quantum Many-Body Systems

Quantum Information and Quantum Many-Body Systems share a common theme: The study of the rich collective phenomena which arise from the complex quantum correlations - entanglement - which build up between the constitutents of the system. This covers exotic phases of matter just as much as the ability of a quantum computer - itself a system of many qubits - to carry out complex computational taks. In my presentation, I will highlight cases where these two fields fruitfully interplay: How insights from entanglement theory provide us with novel tools to probe quantum many-body systems, and how quantum many-body problems yield ways to both verify and use near-term quantum devices.

10. January 2022

Terry Rudolph (Imperial College London)

Quantum computing at the speed of light

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17. January 2022

Paolo Mataloni (University of Rome)

Generalizing spreading phenomena in Optical Quantum Walks

Besides their proposed applications for quantum computing, Quantum Walks (QWs) provide a
general framework to describe coherent propagation phenomena. They allow indeed to describe how quantum
particles move or spread among the sites of a discretized space, for instance, inside a material. Facing real
systems, most of the times very far from being ideal, the difficulty to describe exactly the system itself could
bring to manage very complex problems. In this perspective QWs, in which a finely controlled insertion of
various levels of disorder during the evolution of the walker have been introduced, furnish a suitable
framework to model such systems.
I will report on two experiments in which two different kinds of optical disordered QWs have been adopted
to realize quantum simulators able to model both superdiffusive and transient subdiffusive phenomena,
exhibiting anomalous spreading in space over time. The introduction of a suitable level of disorder within
the QWs makes possible to explore the full range of superdiffusive and subdiffusive behaviors, ranging, for
all experimentally accessible step numbers of the network, from normal diffusion to superdiffusion in the
first experiment and from anomalous Anderson-like localization to normal diffusion in the second one.
Single particle QW evolution has been proven to not possess genuine quantum features since it can be
described by classical wave theory. QW evolution of multiple particles, instead, needs to be featured by
non-classical correlations, such as indistinguishability and entanglement. I will present further
experimental results regarding multiparticle QWs adopted to observe the spreading properties of nonclassical correlations, also in presence of disorder.
In general, QWs can be useful tools for the study of any kind of propagation. For instance, looking at the
system from an informational point of view it is possible to understand the way Quantum Information travels
coherently through a suitable disordered network. In the same context of investigating the Quantum
Information dynamics in a network, recent experimental results dealing with a quantum state discrimination
protocol based on a generalization of the QW model will be also presented.

24. January 2022

Georgios Katsaros (IST Austria)

Semiconductor nanodevices: from basic physics
to quantum information

It is impossible to picture modern life without thinking of the vast amount of microelectronic applications that surround us. However, such development has only been made possible with the invention of the transistor in 1947. This, back at that time few centimeters large device, led to a technological revolution. Today the size of the transistors is less than 14 nm. At such length scales quantum physics comes into play and while this poses a limitation for the classical semiconductor computer, for fundamental physics it represents an amazing challenge. Can semiconductor devices still play a role in the future of computing while moving into the quantum era? In this talk I will discuss the potential of nanoscale semiconductor devices on the path towards a universal quantum computer, covering aspects ranging from basic physics to quantum bits.