New light shed on the development of quantum technologies
Ions immersed in a Bose-Einstein condensate can produce polarons, with properties quite different from those of bare ions. Two separate polarons can interact via condensate density modulation forming a two-body bound state that resembles a bipolaron. In experiments, an optical tweezer is used to place ions in a Paul trap or to freeze ions’ motion, as shown in the image.
Using quantum gas as a coolant sheds new light on the development of future quantum technologies. This is demonstrated by a team of international scientists—including researcher Grigori Astrakharchik, from the UPC’s Department of Physics—who have used state-of-the-art numerical techniques to study how two ionic quasiparticles interact with each other. The results are published in the journal Nature Communications.
Jun 02, 2023
Positively charged ions repel each other. However, when they are immersed in a Bose-Einstein condensate, which is a gas displaying quantum properties at very low temperatures (−273.15°C), the two ions can be attracted to each other. The physical mechanism underlying this attraction is due to the attractive interactions induced by the quantum gas. Despite the fact that even in realistic setups the potential energy of ions is very strong, using a quantum gas as a coolant may bring interesting perspectives for future quantum technologies, such as a quantum computer based on ion chains.
This has been demonstrated by an international team of researchers, including Grigori Astrakharchik, from the Department of Physics of the Universitat Politècnica de Catalunya - BarcelonaTech (UPC). They have used state-of-the-art numerical techniques to study how two ionic quasiparticles interact with each other. The results are published in the journal Nature Communications.
When a single ion is immersed in a Bose-Einstein condensate, it forms a quasiparticle called an ionic Bose polaron. The ion, together with the low-energy excitations of the Bose-Einstein condensate, forms a new quasiparticle.
The authors found different regimes ranging from the quasiparticle picture, where ions slightly perturb the medium, up to a strongly correlated regime, where induced interactions are boosted by the presence of many-body bound states. According to the work, the induced interaction between the ions in this system has unique properties that are not reproducible using neutral impurities.
Researchers have discovered that the occurrence of a many-body bound state, in which many bosons are found close to the ion, strongly modifies the form of the induced quasiparticle interaction (polaron-polaron) as well as its energy scale. A polaron is a quasiparticle composed of an electron and an associated deformation field. Therefore, the study introduces a new class of bipolaronic state in quantum matter.
Furthermore, the paper shows that analytical approaches such as those based on diagrammatic methods are not adequate to describe the many-body properties of atom-ion quantum mixtures.
The findings are of great significance from both a theoretical and an experimental perspective. They are of interest not only for atom-ion physics research, but also for quantum simulation of impurity models and quantum computing with trapped ions. It is the first step towards more complex induced interactions among charged impurities. With the perspective to control such interactions in the laboratory, novel quantum matter interaction phenomena can be explored in the near future.
The international team includes scientists from the Department of Quantum Physics and Astrophysics, and the Institute of Cosmos Sciences (ICCUB) of the University of Barcelona; the Institut für Theoretische Physik of the Leibniz Universität Hannover; the School of Physics of the University of Warsaw (Poland); and the Zentrum für Optische Quantentechnologien, Fachbereich Physik, in Hamburg (Germany).
The work is supported by the Deutsche Forschungsgemeinschaft, the Polish National Agency for Academic Exchange (NAWA), the Secretariat for Universities and Research of the Ministry of Business and Knowledge of the Government of Catalonia, co-funded by the European Regional Development Fund under the FEDER Catalunya programme, and the Spanish Ministry of Economic Affairs and Digital Transformation (MINECO).
