Bavaria, Germany

I'm a computational physicists an **research software engineer** with a focus on high-performance
computing (HPC). As part of the National High-Performance
Computing Alliance (NHR), I
optimize - and help other people optimize - HPC codes and develop tools for monitoring and tuning
the (parallel-)performance of software.

In my research as a **scientist**, I develop and use a variety of novel methods and technologies
to gain insights into quantum systems. In particular, I've developed a **quantum monte carlo**
code (in Julia) to study metallic quantum
criticality, I've used **machine learning** to identify phase transitions
and non-Fermi liquid
physics, I've used the **functional renormalization group** to study the effect of
interactions in graphene, and I've used a (real) **quantum computer** to run parallel
quantum chemistry simulations.

I actively contribute to many free and **open source software projects**, mostly focused on
scientific computing and Julia. In particular, I am a
co-organizer of JuliaCon and, until recently, was
editor-in-chief of the Julia Proceedings.

As a **freelancer**, I offer consulting services and deliver workshops
at public and private institutions. (Feel free to reach out.)

I obtained my PhD in theoretical physics in the Computational Condensed Matter Physics
group of Prof. Simon Trebst
at the University of Cologne. Previously, I worked with Prof. Peter Kopietz and Prof. Roser Valenti
at the Goethe University and the University of Florida. Fortunately, I also had the distinct pleasure
of conducting multi-month research stays at Stanford
University (Prof. Steve Kivelson), the University of
Chicago, and the Weizmann Institute of
Science (Prof. Erez Berg). Besides physics, I took various computer science courses at TU Darmstadt.

In this work, we present numerically exact results from sign-problem free quantum Monte Carlo
simulations for a spin-fermion model near an \(O(3)\) symmetric antiferromagnetic (AFM) quantum
critical point. We find a hierarchy of energy scales (see figure) that emerges near the quantum
critical point, indicating the onset of Landau damping and a transition into a superconducting
\(d-\)wave state.

Reading: paper, talk, code, numerics paper, numerics package, thesis

We demonstrate that a machine learning technique dubbed
quantum loop topography (QLT) can be used to directly probe
transport properties by machine learning current-current correlations in imaginary time. We showcase
this approach by studying the emergence of relevant fluctuations in three systems: the negative-U
Hubbard model, a spin-fermion model for a metallic quantum critical point, and a similar model
describing nematic order. For all systems, we find that the
QLT approach detects a change in transport in very good agreement with their established phase
diagrams. For the models describing spin-density wave and nematic order, QLT reveals an extended
dome-shaped non-Fermi liquid regime.

Reading: paper1, book
article, paper2, thesis

We present a novel parallel hybrid quantum-classical algorithm for the solution of the quantum-chemical
ground-state energy problem on gate-based quantum computers. This approach is based on
the reduced density-matrix functional theory (RDMFT) formulation of the electronic structure
problem. For that purpose, the density-matrix functional of the full system is decomposed into an
indirectly coupled sum of density-matrix functionals for all its subsystems using the adaptive
cluster approximation to RDMFT. The approximations involved in the decomposition and the adaptive
cluster approximation itself can be systematically converged to the exact result. The solutions for
the density-matrix functionals of the effective subsystems involves a constrained minimization over
many-particle states that are approximated by parametrized trial states on the quantum computer
similarly to the variational quantum eigensolver. The independence of the density-matrix functionals
of the effective subsystems introduces a new level of parallelization and allows for the
computational treatment of much larger molecules on a quantum computer with a given qubit count. In
addition, for the proposed algorithm techniques are presented to reduce the qubit count, the number
of quantum programs, as well as its depth. The new approach is demonstrated for Hubbard-like systems
on IBM quantum computers based on superconducting transmon qubits.

Reading: paper,
code

In this work, we take a systematic functional renormalization group (FRG) approach in studying
graphene many-body effects at the Dirac point due to long-range Coulomb interactions. In particular,
we examine the renormalization of the quasiparticle velocity, as observed in experiments, by
establishing a low-energy effective QFT and deriving an infinite hierarchy of exact flow equations.
By means of a scaling dimension analysis, we
deduce a system of coupled integro-differential equations describing the
renormalized quasiparticle velocity and dielectric function in graphene at arbitrary scales.
In the static screening limit, the full numerical solutions indicates that the Dirac cone gets strongly modified by long-range Coulomb interactions in the
vicinity of the Dirac point.

Reading: paper, thesis, talk

I regularly give workshops at universities and private research institutions, mostly with a focus on scientific numerical computing, high-performance computing and research software engineering. If you're curious, feel free to reach out. I'm looking forward to your inquiry!

Julia is a beautiful programming language for numerical computing that is free to use and open source. It explores the tradeoffs in language design for dynamic programming languages and aims to be as accessible as Python while still being as fast as statically compiled languages (eg. C, Fortran). My 4-day course is targeted at researchers who are interested in numerical computing and who want to learn how to write high-performance codes in Julia. To get an impression of the content, check out e.g. this GitHub repository.

"Noctua 2 Supercomputer"**Carsten
Bauer**, Tobias Kenter, Michael Lass, Lukas Mazur, Marius Meyer, Holger Nitsche, Heinrich
Riebler,

Robert Schade, Michael Schwarz, Nils Winnwa, Alex Wiens, Xin Wu, Christian Plessl, and
Jens Simon

Journal of Large-Scale Research Facilities **9**

PC2 /
NHR

"Bridging HPC Communities through the Julia
Programming Language"

Valentin Churavy, William F Godoy, **Carsten Bauer**,
Hendrik Ranocha, Michael Schlottke-Lakemper, Ludovic Räss,

Johannes Blaschke, Mosè Giordano,
Erik Schnetter, Samuel Omlin, Jeffrey S. Vetter, and Alan Edelman

arXiv:2211.02740

PC2 - MIT - ORNL - NERSC - HLRS - CSCS - and more

"Parallel
Quantum Chemistry on Noisy Intermediate-Scale Quantum Computers"

Robert Schade,
**Carsten Bauer**, Konstantin Tamoev, Lukas Mazur, Christian Plessl, and Thomas D. Kühne

Phys.
Rev. Research **4**, 033160

PC2 / NHR

"Identification
of Non-Fermi Liquid Physics in a Quantum Critical Metal via Quantum Loop
Topography"

George Driskell, Samuel Lederer, **Carsten Bauer**, Simon Trebst, and
Eun-Ah Kim

Phys. Rev. Lett. **127**, 046601

Cologne -
Cornell

PhD thesis: "Simulating and machine
learning quantum criticality in a nearly antiferromagnetic metal"

Advisor: Prof. Dr.
Simon Trebst

Thesis PDF, Defense Talk

"Fast and stable determinant
Quantum Monte Carlo"**Carsten Bauer**

SciPost Phys. Core 2, 2 (source code @ GitHub)

Cologne

"Hierarchy of energy scales
in an O(3) symmetric
antiferromagnetic quantum critical metal: a Monte Carlo study"

**Carsten Bauer**, Yoni Schattner, Simon Trebst, and Erez Berg

Phys. Rev. Research **2**, 023008 (source code @
GitHub)

Cologne - Stanford - Weizmann

"Machine
Learning Transport Properties in Quantum
Many-Fermion Simulations" (record
entry)**Carsten Bauer**, Simon Trebst

In NIC Symposium 2020, Vol. 50, pp. 85–92,
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag

Cologne

"Probing transport in
quantum many-fermion simulations via quantum loop topography"

Yi Zhang, **Carsten
Bauer**, Peter Broecker, Simon Trebst, and Eun-Ah Kim

Phys. Rev. B **99**, 161120(R),
Editors' Suggestion

Cologne - Cornell

"Nonperturbative
renormalization group calculation of quasiparticle velocity and dielectric function of
graphene"**Carsten Bauer**, Andreas Rückriegel, Anand Sharma, and Peter
Kopietz

Phys. Rev. B **92**, 121409(R)

Frankfurt

Master's thesis: "Quasi-particle velocity
renormalization in graphene"

Invited talk @ University of Cologne: "Quasi-particle velocity
renormalization in graphene"

Advisor: Prof.
Dr. Peter Kopietz

"Microwave-based
tumor localization in moderate heterogeneous breast tissue"

Jochen Moll, **Carsten
Bauer**, and Viktor Krozer

International Radar Symposium (Dresden,
Germany), pp.877-884

Frankfurt