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.

Marts 2026: Hvis du gerne vil læse om sandsynligheden for overrepræsentation ved danske folketingsvalg klik her.

Hvis du er journalist kan du kontakte mig på +45 40372316.

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

Preprints on the mathematics of electoral systems. Explaination in Danish in March 2026.

Denne artikel udregner sandsynligheden for at Folketingets største parti får flere kredsmandater end det mandattal deres samlede stemmetal svarer til.
• F. R. Klausen.
  Sandsynligheden for overrepræsentation ved Folketingsvalg, 2025. Download (PDF)
Forholdet mellem geografisk repræsentation og proportionel repræsentation er en udfordring for alle valgsystemer. Faktisk kan man bevise at et valgsystem ikke kan have perfekt geografisk repræsentation, proportionel repræsentation og en fast parlamentstørrelse. Det førte blandt andet til at størrelsen på Tysklands parlament voksede med over 100 medlemmer.
• S. Holdum, F. R. Klausen.
  Impossibility Theorem for Two-Tier Electoral Systems, 2025. Download (PDF)
Hvis man kun interesserer sig for blokkenes størrelse hvornår kan det så betale sig at stemme på et parti tæt på spærregrænsen? Det har jeg regnet ud i det følgende. Hvis man stemmer på et parti der i en meningsmåling er lige på spærregrænsen vægter stemmen ca. dobbelt.
• F. R. Klausen.
  The Disproportionate Power of Votes Near Electoral Thresholds, 2025. Download (PDF)

Publications

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

• 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.

• 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.

• 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, A. Lauritzen.
  A stochastic cellular automaton model of culture formation , Phys. Rev. E, 108, 054307, 2023.


• 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.


• 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 , 2014.


• 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, 2014.

Preprints

• U. T. Hansen, J. Jiang, F. R. Klausen
  General coupling for Ising models and beyond , 2025.

• F. R. Klausen, A. Werner.
  Spectra of Lindbladians on the infinite line: From non-Hermitian to full evolution via tridiagonal Laurent matrices , 2022.
• J. Elklit, S. Holudm, F. R. Klausen.
  What is wrong with the proportionality in the Parliamentary Elections Act—and what can be done about it? , (accepted in) Politica, 2025.