Community Research and Development Information Service - CORDIS

Periodic Report Summary 1 - MAG-QUPT (Exploring magnetic quantum phase transitions with ultra-cold Fermi gases)

Project objectives
This project aims at developing a platform for the experimental simulation of quantum phase transitions and quantum critical phenomena using ultra-cold atomic gases. The final project goal is to exploit the unique properties of ultra-cold Fermi gases trapped in optical lattices of adjustable geometries to study quantum phase transitions between spin systems in different lattice structures. More immediate goals are the construction and validation of an experimental apparatus optimized for this type of studies, and the development of experimental tools for the characterization of quantum critical phenomena in quantum gases.

Work performed
During the first period the experimental apparatus on which the project is based has been designed, constructed and validated, including the development of: (i) a potassium cold atom source (2D MOT); (ii) an ultra-high vacuum science chamber; (iii) a laser system for the manipulation of the three potassium isotopes; (iv) Bitter-type electromagnets and a precise stabilization system for the magnetic trap and the control of interatomic interactions using Feshbach resonances; (v) a crossed optical dipole trap; (vi) a high numerical aperture imaging system. At the end of this period we have our disposal a state-of-the-art experimental apparatus which routinely produces Bose-Einstein condensates (BEC) of the two bosonic isotopes of potassium (41K and 39K), and is already prepared for cooling to quantum degeneracy the fermionic one (40K).

Main results
The main results obtained are: (i) observation of BEC of 41K in our experimental apparatus; (ii) cooling of 39K to BEC by sympathetic cooling with 41K; (iii) first observation of double BEC of 39K and 41K; (iv) Feshbach spectroscopy of 39K-41K mixtures, as well as of spin mixtures of 39K and 41K, and comparison of the results with an asymptotic bound state model and numerical coupled-channel calculations; (v) observation of the miscible-immiscible phase transition in a repulsive 39K-41K mixture; (vi) preliminary experimental results on the quantum mechanical stabilization of collapsing Bose-Bose mixtures due to quantum fluctuations (with spin mixtures of both 39K and 41K).

Expected final results
In the second period of the project, the objectives are two-fold: (i) pursue experiments with harmonically trapped repulsively interacting Bose-Bose mixtures. We plan to use this system as test bed for studying quantum critical phenomena, exploiting the miscible-immiscible quantum phase transition due to its conceptual simplicity, and developing adequate tools to characterize it; (ii) work in parallel on the construction of an optical lattice setup, and on the preparation of a quantum degenerate Fermi gas. Once both objectives are achieved, they will be combined to study quantum criticality in fermionic spin systems, the original objective of the project.

Potential impact
In this period our project has provided two technical results useful outside the quantum simulation community: (ii) a novel method for achieving BEC of 39K by sympathetic cooling with 41K, which has a higher duty cycle than the standard approach using 87Rb and might be useful for atom interferometry experiments; (ii) the precise characterization of 39K-41K scattering properties by Feshbach spectroscopy, which could improve the available model interaction potentials for potassium.

Reported by



Life Sciences
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