Description
Collisions between ultracold quantum gases provide a fertile ground for generating nonclassical correlations, entanglement, and momentum-space analogues of optical quantum states using massive particles. Such phenomena have been studied extensively in bosonic systems, in particular in collisions of metastable $^4$He$^\ast$ Bose--Einstein condensates. These studies led to some of the foundational experiments in quantum-atom optics, including demonstrations of the atomic analogues of the Hanbury Brown--Twiss effect, the Hong--Ou--Mandel effect, violation of the classical Cauchy--Schwarz inequality with matter waves, and demonstrations of Bell correlations between momentum-entangled $^4$He$^\ast$ atoms.
Related phenomena involving mixed Bose--Fermi gases have, however, remained largely unexplored and are becoming the focus of next-generation collision experiments. Here, we present a theoretical study of collisions between Bose and Fermi gases of metastable helium, motivated by the recent dual-species experiments with $^4$He$^\ast$ and $^3$He$^\ast$.
The unique combination of Bose and Fermi quantum statistics, together with single-atom-resolved detection available in metastable-helium experiments, enables direct access to atom--atom correlation functions and momentum-space entanglement. We develop a microscopic description of Bose--Fermi collisions and analyse the resulting Bose--Bose, Fermi--Fermi, and Bose--Fermi correlations.
Our results predict characteristic signatures of the Bose--Fermi collisional halo and cross-species correlations that have no analogue in purely bosonic or purely fermionic collision systems. These correlations provide a pathway towards the generation of entangled states involving atoms of different masses and quantum statistics, opening new opportunities for fundamental tests of quantum mechanics, including Bell tests with entangled atoms of different masses, quantum tests of the weak equivalence principle, and potential probes of quantum gravity involving entanglement between massive particles.
| I am the presenting author | Yes |
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