The 12th Workshop on Quantum Chaos and Localisation Phenomena was held in Warsaw, Poland, on May 23–24, 2025, in the Institute of Physics of the Polish Academy of Sciences. Once again, it was fully virtual and took place on the Zoom platform. The Workshop was organized by the Institute of Physics of the Polish Academy of Sciences, the Center for Theoretical Physics of the Polish Academy of Sciences, and the Foundation "Pro-Physica". The first of these biennial workshops was organized in 2003. Selected articles of the invited lectures, starting from the second Workshop, were published in the journal Acta Physica Polonica A [1–10]. The main objectives of these workshops are to assess achievements and formulate directions for new research on quantum chaos and localisation phenomena. 
 
The Workshop gathered 30 officially registered participants from Afghanistan, China, the Czech Republic, France, Germany, Israel, Mexico, Poland, Sweden, the United Kingdom, and the USA, representing experimental and theoretical physicists. Additionally, about 20 participants (mainly Ph.D. students and doctors) had the opportunity to join the Workshop via the Zoom platform. The lectures were also attended by non-registered researchers and Ph.D. students of the Institute of Physics and the Center for Theoretical Physics on the Institute's YouTube channel. During the meeting, 16 invited lectures and 2 posters were presented. The presentations focused on the following topics: quantum chaos and non-linear classical systems, quantum and microwave graphs and billiards, localisation phenomena, topological effects, and physics of low-dimensional systems. Talks and poster presentations addressed theoretical and experimental problems from various fields of solid state, atomic and molecular, and mathematical physics and quantum computers. It is noteworthy to mention that, although most of the lectures were devoted to the theory of quantum chaos and many-body systems, there were also very interesting, quite new topics, such as topological effects and the applications of chaotic systems to the modelling of metamaterials. In most of the theoretical presentations, the mathematical aspects of the discussed topics played a dominant role. On the other hand, several presentations focused on the experimental validation of new theoretical findings.

Since the meeting was held online, this time scientific discussions, traditionally held during coffee breaks and social events, took place between lectures and during visits to the "rooms", where the posters were displayed.

On behalf of the organizers, we would like to express our gratitude to all the speakers and the authors of the poster presentations for their contribution to the success of the Workshop. 

We present the Proceedings of the 12th Workshop on Quantum Chaos and Localisation Phenomena, in which 7 invited articles of the Workshop participants are published. We would like to thank the reviewers who contributed to achieving such an outstanding scientific level of the presented works.

Szymon Bauch
Michał Ławniczak
Leszek Sirko

Editors of the Proceedings

[1] L. Sirko, S. Bauch, Acta Phys. Pol. A 109 (1), (2006)

[2] L. Sirko, S. Bauch, Acta Phys. Pol. A 112 (4), (2007)

[3] L. Sirko, S. Bauch, Acta Phys. Pol. A 116 (5), (2009)

[4] L. Sirko, S. Bauch, Acta Phys. Pol. A 120 (6-A), (2011)

[5] L. Sirko, S. Bauch, Acta Phys. Pol. A 124 (6), (2013)

[6] L. Sirko, S. Bauch, Acta Phys. Pol. A 128 (6), (2015)

[7] L. Sirko, S. Bauch, Acta Phys. Pol. A 132 (6), (2017)

[8] L. Sirko, S. Bauch, Acta Phys. Pol. A 136 (5), (2019)

[9] S. Bauch, L. Sirko, Acta Phys. Pol. A 140 (6), (2021)

[10] S. Bauch, L. Sirko, Acta Phys. Pol. A 144 (6), (2023)