Frederik Ravn Klausen

Postdoctoral Researcher
University of Cambridge

Email: frk23@cam.ac.uk

Mathematician working quantitatively with complex systems: quantum, classical and electoral at University of Cambridge. Before that I was at Princeton and in QMATH and NQCP at the University of Copenhagen.

Contact: Danish code, 40 37 23 16.

Below you will find an overview of my research interests as well as a list of publications.

Publications

A list of my publications can also be found on Google Scholar.

Percolation and the Ising model

• J. Jiang, F. R. Klausen.
  A simple proof of exponential decay for the near-critical planar Ising model, Letters in Mathematical Physics, 116, 125, 2026.
• U. T. Hansen, J. Jiang, F. R. Klausen.
  A general coupling for Ising models and beyond, Electronic Journal of Probability, 31, 1-32, 2026.
• R. Gross, E. Kammerer, F. R. Klausen.
  From Kreweras walks to branching perimeter processes of percolated triangulations, Preprint, 2026.
• U. T. Hansen, F. R. Klausen.
  The End of the Double Random Current, Preprint, 2026.
• U. T. Hansen, F. R. Klausen.
  The Supercritical Loop O(1) and Random Current models: Uniqueness and Mixing, Preprint, 2026.
• F. R. Klausen, N. Kravitz.
  Half-plane non-coexistence without FKG, Preprint, 2026.
• U. Thinggaard Hansen, F. R. Klausen, P. Wildemann.
  Non-uniqueness of phase transitions for graphical representations of the Ising model on tree-like graphs, ALEA, Latin American Journal of Probability and Mathematical Statistics, 22, 889-904, 2025.
• U. Hansen, B. Kjær, F. R. Klausen.
  The Uniform Even Subgraph and Its Connection to Phase Transitions of Graphical Representations of the Ising Model, Communications in Mathematical Physics, 2025.
• U. Hansen, F. R. Klausen.
  Strict monotonicity, continuity and bounds on the Kertész line for the random-cluster model on ℤ^d, Journal of Mathematical Physics, 2023.
• F. R. Klausen, A. Raoufi.
  Mass scaling of the near-critical 2D Ising model using random currents, Journal of Statistical Physics, 2022.
• F. R. Klausen.
  On monotonicity and couplings of random currents and the loop-O(1)-model, ALEA, Latin American Journal of Probability and Mathematical Statistics, 2022.

Electoral systems

• S. T. Holdum, F. R. Klausen.
  Impossibility theorem for two-tier electoral systems, Annals of Operations Research, 2026.
• F. R. Klausen.
  Sandsynligheden for overrepræsentation ved Folketingsvalg, Politica, 2026.
• F. R. Klausen.
  Ensuring proportionality: a logical model for compensatory seats added to multi-member constituencies, Preprint, 2026.
• F. R. Klausen.
  The Disproportionate Power of Votes Near Electoral Thresholds, Preprint, 2025.
• J. Elklit, S. Holdum, F. R. Klausen.
  What is wrong with the proportionality in the Parliamentary Elections Act—and what can be done about it?, Politica, 2025.

Quantum information

• A. J. Bay-Smidt, F. R. Klausen, C. Sünderhauf, R. Izsák, G. C. Solomon, N. S. Blunt.
  Fault-Tolerant Quantum Simulation of Generalized Hubbard Models, PRX Quantum, 6, 030348, 2025.
• F. R. Klausen, S. Warzel.
  Decoherence is an echo of Anderson localization in open quantum systems, Annales Henri Poincaré, 2025.
• D. Harley, I. Datta, F. R. Klausen, A. Bluhm, D. S. França, A. Werner, M. Christandl.
  Going Beyond Gadgets: The Importance of Scalability for Analogue Quantum Simulators, Nature Communications, 2024.
• F. R. Klausen.
  Spectra of generators of Markovian evolution in the thermodynamic limit: From non-Hermitian to full evolution via tridiagonal Laurent matrices, Preprint, 2022.

Miscellaneous

• F. R. Klausen, A. Lauritsen.
  A stochastic cellular automaton model of culture formation, Phys. Rev. E, 108, 054307, 2023.
• A. Bluhm, M. Christandl, F. Gesmundo, F. R. Klausen, L. Mančinska, V. Steffan, D. S. França, A. Werner.
  SARS-CoV-2 transmission routes from genetic data: A Danish case study, PloS One, 2020.
• P. Jensen, F. R. Klausen, P. Rasmussen.
  Combinatorial classification of quantum lens spaces, Pacific Journal of Mathematics, 2018.
• S. Holdum, F. R. Klausen, P. Rasmussen.
  Powers in Prime Bases and a Problem on the Central Binomial Coefficient, Integers: Electronic Journal of Combinatorial Number Theory, 2015.
• S. Holdum, F. R. Klausen, P. Rasmussen.
  On a Conjecture on the Representation of Positive Integers as the Sum of Three Terms of the Sequence ⌊n² / a⌋, The Journal of Integer Sequences, 2015.

Coauthors

Andreas Bay-Smidt, Andreas Bluhm, Nick Blunt, Matthias Christandl, Ishaun Datta, Jørgen Elklit, Daniel Stilck França, Fulvio Gesmundo, Renan Gross, Ulrik Thinggaard Hansen, Dylan Harley, Sebastian Holdum, Róbert Izsák, Peter Lunding Jensen, Jianping Jiang, Emmanuel Kammerer, Boris Kjær, Noah Kravitz, Asbjørn Bækgaard Lauritsen, Laura Mančinska, Aran Raoufi, Peter M. R. Rasmussen, Gemma C. Solomon, Vincent Steffan, Christoph Sünderhauf, Simone Warzel, Albert H. Werner, Peter Wildemann