Open questions in the quantum many-body problem
Guest editor: Yvan Castin; Carlos Sá de Melo
Yvan Castin is Senior Researcher at the CNRS. A theoretician, he has been working at the Laboratoire Kastler Brossel, École normale supérieure, Paris, since his doctoral thesis on laser cooling of atoms, carried out under the supervision of Jean Dalibard and Claude Cohen-Tannoudji from 1988 to 1992. Together with Klaus Mølmer and Jean Dalibard, he contributed to the development of the Monte Carlo wave function method. Since 1995, he has been working on gaseous atomic Bose-Einstein condensates in the "cold atom" group set up by Claude Cohen-Tannoudji, before adding strongly interacting fermion superfluids as a second string to his bow in 2004, following Christophe Salomon in the "ultracold Fermi gases" group, of which he is responsible for the theoretical part. He is responsible for several original results on the four-body Efimov effect and cluster expansion for the unitary fermion gas, spin squeezing limits and coherence time of a condensate in an isolated Bose gas, and collisionless sound damping in superfluids, in collaboration with Alice Sinatra, Ludovic Pricoupenko, Felix Werner, Shimpei Endo, and others. He received (with Laurent Lafforgue) the Jacques Herbrand prize from the Académie des Sciences in 2001, and in 2012 the Louis D. Foundation team prize, awarded to group leader Christophe Salomon.
Prof. Carlos A. R. Sá de Melo earned a PhD in theoretical physics at Stanford University (1991), specializing in quantum many-body physics, under the supervision of Prof. Sebastian Doniach (Bardeen Prize 2018), and was a postdoctoral fellow at the Science and Technology Center for Superconductivity in Illinois, mentored by Dr. Alexei Abrikosov (Nobel Prize 2003, deceased). After that he moved to the Georgia Institute of the Technology, where he is a professor of physics today. Prof. Sá de Melo is best known for his theoretical contributions to the evolution from Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensation (BEC) superfluidity in single- and two-band systems during the 1990’s and 2000’s, a phenomenon explored experimentally since the mid-2000’s. For his work on ultracold Fermi atoms and superfluids, he was awarded a two-year Visiting Fellow position at the Joint Quantum Institute (UMD-NIST) from 2006-2008, was elected Fellow of the American Physical Society in 2012, was granted a Simons Fellowship in 2017 for an extended visit to the Galileo Galilei Institute of Theoretical Physics (Florence, Italy), was presented the Fibonacci Prize in 2018 at the Quantum Complex Matter conference (Frascati, Italy), was elected Fellow of the American Association for the Advancement of Science in 2021, and was honored with a Mercator Fellowship by the German Research Foundation in 2024. His research on the crossover and quantum phase transitions from the BCS to the BEC regime in superfluids has influenced experimental and theoretical work not only in atomic, but also in nuclear and condensed matter physics.
Yvan Castin; Carlos Sá de Melo (ed). Open questions in the quantum many-body problem. Comptes Rendus. Physique, Volume 25 (2024) no. S6, doi : 10.5802/crphys.sp.3. https://comptes-rendus.academie-sciences.fr/physique/item/CRPHYS_2024__25_S6/
In physics, the quantum many-body problem is a highly unifying current research topic, since it touches a large number of fields, from mathematical physics to condensed matter, atomic physics and quantum optics, and involves numerous systems, from superconductors to quantum gases, spin systems, topological matter, disordered systems and dissipative photonic systems, in dimension three or reduced dimensions, with short- or long-range interactions, etc. It raises particularly challenging questions, requiring the cross-fertilization of a wide range of study methods: mathematical, analytical, macroscopic or effective low-energy, diagrammatic, numerical, experimental, quantum simulation, and more.
Although there are many congresses in this field, they are generally limited to brief presentations of the results already obtained, and specialize in one of the aspects mentioned. As far as we know, very few of them try to take stock of the open questions and the main directions to be explored, in the spirit of the famous Solvay congresses of yesteryear, by bringing together researchers from different fields with sufficient vision and maturity to give long (90-minute) foresight presentations on the blackboard (no projection), with plenty of time for discussion. This is what we did in July 2024, with about fifteen presentations over five days of a symposium open to all in the large Hermite amphitheatre at the Institut Henri Poincaré (IHP) in Paris. The presentations were recorded and posted online on the IHP’s Carmin channel (click here).
To make the exercise as valuable as possible, we wanted the colloquium to leave a written trace – verba volant –, hence the present special issue published in open access in Comptes Rendus Physique, which brings together the various contributions in the form of conference proceedings. We hope this will encourage the community of researchers, PhD students and postdocs to focus on the big questions and to build bridges between the different disciplines of quantum many-body physics.
We would like to express our sincere gratitude to the speakers who accepted the extra work involved in writing the proceedings, and to the management of the IHP, who graciously made their infrastructure and technical team available to us, waiving the cost of renting the amphitheatre. Last but not least, we are grateful to Stephan Fauve for enthusiastically accepting our special issue, and to Isabelle Vallet for efficiently guiding its implementation.
[Open questions for strongly interacting Fermi gases with zero-range interactions]