Pieter W. Claeys



Max Planck Institute for the Physics of Complex Systems

13 June 2022

The word is out! I am starting my own group as a Research Group Leader at the Max Planck Institute for the Physics of Complex Systems in Dresden. My group on the Dynamics of Quantum Information is embedded in the Division Condensed Matter. Extremely excited about this!

Do check out the group's website!

Two new publications

16 June 2022

Two new papers just appeared online! Our work on Emergent quantum state designs and biunitarity in dual-unitary circuit dynamics was published in Quantum, and our paper on the Absence of Superdiffusion in Certain Random Spin Models appeared in Physical Review Letters. Abstracts below.

Do check out the Quantum page to read more about our article, including a popular summary!

Recent works have investigated the emergence of a new kind of random matrix behaviour in unitary dynamics following a quantum quench. Starting from a time-evolved state, an ensemble of pure states supported on a small subsystem can be generated by performing projective measurements on the remainder of the system, leading to a projected ensemble. In chaotic quantum systems it was conjectured that such projected ensembles become indistinguishable from the uniform Haar-random ensemble and lead to a quantum state design. Exact results were recently presented by Ho and Choi [Phys. Rev. Lett. 128, 060601 (2022)] for the kicked Ising model at the self-dual point. We provide an alternative construction that can be extended to general chaotic dual-unitary circuits with solvable initial states and measurements, highlighting the role of the underlying dual-unitarity and further showing how dual-unitary circuit models exhibit both exact solvability and random matrix behaviour. Building on results from biunitary connections, we show how complex Hadamard matrices and unitary error bases both lead to solvable measurement schemes.

The dynamics of spin at finite temperature in the spin-1/2 Heisenberg chain was found to be superdiffusive in numerous recent numerical and experimental studies. Theoretical approaches to this problem have emphasized the role of nonabelian SU(2) symmetry as well as integrability, but the associated methods cannot be readily applied when integrability is broken. We examine spin transport in a spin-1/2 chain in which the exchange couplings fluctuate in space and time around a nonzero mean J, a model introduced by De Nardis et al. [Phys. Rev. Lett. 127, 057201 (2021).]. We show that operator dynamics in the strong noise limit at infinite temperature can be analyzed using conventional perturbation theory as an expansion in J. We find that regular diffusion persists at long times, albeit with an enhanced diffusion constant. The finite time spin dynamics is analyzed and compared with matrix product operator simulations.

Quantum chaos and holography

31 May 2022

I was one of the invited speakers at the Chahol22 Workshop on Quantum Chaos and Holography, presenting some upcoming works on combining dual-unitary dynamics with projective measurements. A full program, including an impressive list of speakers, can be found here. (The logo might again look familiar!)

This five-day workshop will facilitate an intensive exchange of ideas between string theorists, condensed matter physicists, atomic physicists, mathematical physicists and researchers with other areas of expertise actively working on theory and applications of quantum chaos. The main goals of the workshop is both to introduce researches from different communities to key models and results and to outline unresolved problems actively investigated by these different communities. Such a meeting should allow us to consolidate new ways of quantifying many-body quantum chaos and highlight their implications for important questions of different disciplines. The main themes include studying signatures of chaos in quantum many-body systems, developing physical applications to thermalization and transport, developing new theoretical techniques for studying quantum chaos in complex systems, and exploring implications of chaos to related  fields, such as quantum information and the quantum mechanics of black holes. We now describe key issues of each of these themes more explicitly.