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Theoretical physicists working at a blackboard collaboration pod in the Beecroft building.
Credit: Jack Hobhouse

Dr Adam Nahum

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Sub department

  • Rudolf Peierls Centre for Theoretical Physics

Research groups

  • Condensed Matter Theory
  • About
  • Publications

Spacetime picture for entanglement generation in noisy fermion chains

Physical Review B American Physical Society (APS) 112:6 (2025) 064301

Authors:

Tobias Swann, Denis Bernard, Adam Nahum

Abstract:

Studies of random unitary circuits have shown that the calculation of Rényi entropies of entanglement can be mapped to classical statistical mechanics problems in spacetime. In this paper, we develop an analogous spacetime picture of entanglement generation for random free or weakly interacting fermion systems without conservation laws. We first study a free-fermion model, namely a one-dimensional chain of Majorana modes with nearest-neighbor hoppings, random in both space and time. We analyze the N th Rényi entropy of entanglement using a replica formalism, and we show that the effective model is equivalent to an SO ( 2 N ) Heisenberg spin chain evolving in imaginary time. By applying a saddle-point approximation to the coherent states path integral for the N = 2 case, we arrive at a semiclassical picture for the dynamics of the entanglement purity, in terms of two classical fields in spacetime. The classical solutions involve a smooth domain wall that interpolates between two values, with the width of this smooth domain wall spreading diffusively in time. We then study how adding weak interactions to the free-fermion model modifies this spacetime picture. Interactions reduce the symmetry of the effective continuum description. As a result the width of the entanglement domain wall remains finite, rather than growing diffusively in time. This yields a crossover from diffusive to ballistic spreading of information.
More details from the publisher

Bayesian critical points in classical lattice models

(2025)

Authors:

Adam Nahum, Jesper Lykke Jacobsen
Details from ArXiV

Monitored fermions with conserved U(1) charge

Physical Review Research American Physical Society (APS) 6:4 (2024) 043246

Authors:

Michele Fava, Lorenzo Piroli, Denis Bernard, Adam Nahum
More details from the publisher

Heisenberg spin chain with random-sign couplings

Proceedings of the National Academy of Sciences of the United States of America Proceedings of the National Academy of Sciences 121:36 (2024) e2401292121

Authors:

Michele Fava, Jesper Lykke Jacobsen, Adam Nahum
More details from the publisher
More details

Worldsheet patching, 1-form symmetries, and Landau* phase transitions

Physical Review B American Physical Society (APS) 110:11 (2024) 115102

Authors:

Pablo Serna, Andrés M Somoza, Adam Nahum
More details from the publisher

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