## QUANTUM MANY BODY THEORY GROUP @ LMU

Welcome to our webpage! Our group is based at LMU Munich, part of the chair of Theoretical Nanophysics, the Arnold Sommerfeld Center for Theoretical Physics, and the Munich Center for Quantum Science an Technology (MCQST).

>> 11/2023: We published a series of papers 1, 2, 3 on arXiv.org shedding light on the origins of high-Tc superconductivity in bilayer nickelates LNO under pressure!

>> 10/2023: We published a pre-print of our review on Cold-atom quantum simulators of gauge theories!

>> 06/2023: Our paper on realizing 1/2-Laughlin states with ultracold atoms has been published in Nature! See e.g. physicsworld coverage for a summary.

>> 01/2023: Our paper on magnetically mediated hole pairing has been published in Nature! See the accompanying Nature research briefing for a crisp description.

>> 12/2022: Video streams of our ITAMP workshop on "Quantum Simulation of doped Hubbard Systems" are available on the ITAMP YouYube channel now!

>> 11/2022: We're organizing an ITAMP workshop on "Quantum Simulation of doped Hubbard Systems" from Nov. 14-16, 2022. Sign up here if you want to participate!

>> 10/2022: Our incoming PhD students received prestigious fellowships: Hannah Lange (IMPRS-QST fellowship) and Tim Harris (MQV fellowship) - congratulations!

>> 05/2022: Strong hole-pairing covered by Phys.org!

>> 04/2022: Our paper on strong pairing in bilayer antiferromagnets has been published in Nature physics, and highlighted in a News & Views article: "Pairing with strings attached"!

>> 04/2022: Our Heraeus conference on Frontiers of Quantum Gas Microscopy starts on Apr. 03 with an amazing lineup of speakers!

>> 12/2021: Our review on the Exploration of doped quantum magnets with ultracold atoms has been published!

>> 12/2021: Applications are now accepted (here) for our upcoming Heraeus conference on Frontiers of Quantum Gas Microscopy!

>> 10/2021: Our PI, Fabian Grusdt, holds a tenure-track professorship at LMU!

>> 09/2021: Our group member, Lukas Homeier, received a PhD fellowship by the Studienstiftung - congratulations!

>> 08/2021: Our collaborator Annabelle Bohrdt receives the 2nd place Quantum Future Award 2021 - congratulations!

>> 08/2020: ERC Starting Grant awarded for our upcoming project (featured by MCQST): Simulating ultracold correlated quantum matter (SimUcQuam)

>> 06/2020: Our collaborator Christie Chiu receives the Deborah Jin thesis prize at DAMOP!

>> 01/2020: MCQST START fellowship starts.

>> 12/2019: Harvard Physics Newsletter - cover story.

>> 11/2019: MCQST News: Making synthetic gauge fields quantum.

>> 09/2019: News & Views: "Engaged in gauge theory".

>> 08/2019: Nature cover: " A magnetic moment".

>> 07/2019: Science Perspective: "Polarons leave a trace".

>> 07/2019: TUM: "Which one is the perfect quantum theory?".

>> 05/2018: APS Synopsis: "ARPES with Cold Atoms".

>> 06/2017: Phys.org: "Physicists create antiferromagnet..." & Nature News & Views: "A firmer grip on the Hubbard model".

>> 06/2017: Nature News & Views: "Interactions propel a magnetic dance".

>> 06/2016: Nat. Phys. Research Highlight: "Impurities for sensors".

### Join the group:

Open positions will be posted here as they become available!

### Research interests:

Here is a quick list summarizing my key research interests:

Strongly correlated quantum many-body systems

Quantum simulation with ultracold atoms and photons

Many-body systems with topological order

Fractional quantum Hall effect & frustrated quantum magnets

Interacting electrons and high-temperature superconductivity

Non-equilibrium dynamics in quantum systems

Impurity and polaron physics

Here is a more detailed summary of my research accessible also for non-experts:

The main goal of my research is to learn more about nature. As a condensed-matter physicist, this primarily means I am interested in the behavior of exotic phases of matter. Sometimes interactions become dominant and they determine all key properties of a physical phase. Such effects can have immediate practical relevance, like in the case of high-temperature superconductors, or they can be more of academic interest. Often one can't even tell, and problems that are considered of purely academic interest suddenly turn out to be of immense practical importance, or real-world observations pose immense challenges in their theoretical explanation.

There are many ways to make progress in understanding strongly correlated materials, ranging from purely experimental approaches to highly developed mathematical treatments. My research is theoretical, but with a strong connection to ongoing experiments. Besides consistent theoretical descriptions of physical effects I'm always searching for clear and simple explanations. This approach is particularly powerful in the context of quantum simulations, where the underlying models are very well defined and elementary enough to uncover the most fundamental mechanisms how nature works.

With the introduction of a variety of quantum simulation platforms during the last decade - ranging from ultracold atoms and strongly interacting photons to arrays of superconducting qubits - my generation of physicists has the unique opportunity to explore strongly correlated many-body systems from an entirely new perspective. Not only can the most interesting model systems, like the two-dimensional Fermi-Hubbard Hamiltonian, be studied. New experimental capabilities also allow to directly measure exotic non-local order parameters and resolve quantum effects taking place inside complicated many-body systems on the level of single particles on individual lattice sites.

The theoretical approaches used in my research are directly related to the new experimental capabilities. To fully understand the behavior of a system as a whole, it is crucial to understand its microscopic details. One promising strategy is to start by studying impurity physics. For example, a single hole inside an anti-ferromagnet can be understood as an impurity. When it becomes mobile it interacts with the surrounding spin system, and these interactions strongly modify (or dress) its properties. Loosely speaking, a high-temperature superconductor is obtained when the number of holes in such a system is increased. One of my long-term research goals is to develop a better microscopic understanding of high-temperature superconductivity which fully includes the mechanisms that dress a single hole inside an anti-ferromagnet.

Impurities can behave very differently depending on the many-body system through which they are moving. In my research I am interested as much in the properties of the impurities themselves, as in the properties of the surrounding many-body systems. Examples include spin-full impurity particles inside fractional quantum Hall systems or quantum spin liquids (with possible applications for topological quantum computation), light atoms interacting strongly with a surrounding Bose-Einstein condensate or impurities inside strongly correlated one-dimensional systems. My most recent research focuses on light holes doped into quantum magnets and their role in the problem of understanding high-temperature superconductivity and the elusive pseudogap phase in particular.