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Topological states with Spin-Dependent potentials for ultracold lithium

Periodic Reporting for period 1 - TopSpiD (Topological states with Spin-Dependent potentials for ultracold lithium)

Reporting period: 2018-07-01 to 2020-06-30

Majorana fermions are a type of fermions that is its own antiparticle. They exhibit non-trivial braiding properties. Producing such excitations is an important challenge of experimental physics since it is predicted to allow for protected topological quantum computing. While particles with such a statistics have not yet been found, the existence of excitations of strongly correlated systems with the same properties as Majorana Fermions has been predicted. This project was aimed at creating topological excitations such as Majorana Fermions on an ultracold atom experimental setup suited for studying transport phenomena.

This task is bound to be challenging for an ultracold atom experiment because one needs both a fermionic superfluid and implement a spin-orbit coupling mechanism. While the former is easily achieved for lithium 6 atoms thanks to its broad Feshbach resonance, the latter is more involved since the small fine structure splitting leads to increased heating when using near-resonant light beams. In the course of this fellowship, several steps have been taken to produce this kind of excitations.
Technical improvements of the existing experimental setup:
The experimental setup has been adapted to produce novel atomtronics structures and these excitations. This has involved implementing far- and near-resonant beams with light-shaping techniques using digital micromirror devices. Therefore, the power, frequency and shape of the potentials can be accurately tuned.

Realization of a spin filter:
By properly choosing the frequency of a near-resonant beam, we have realized a spin-filter for ultracold atoms [2]. We have demonstrated that dissipation effects due to the scattering of photons can be modeled and are not preventing the observation of quantized plateaus of conductance [1].

Investigating possible realizations of topological systems:
In the course of this fellowship, many theory collaborations have been established to fully understand the possibilities offered by the system. This has resulted in the publication of a theoretical proposal on the realization of a Hall geometry using synthetic dimensions [3].

Investigating strongly correlated systems:
In order to realize topological excitations, one needs to combine near-resonant Raman beams together with a paired fermionic superfluid. Previous studies on the experimental setup and theory collaborations have shown the complexity of transport through a structured central region combined with a normal to superfluid transition. Therefore, data is being analyzed on the transport of heat and particles both at unitarity and in non-interacting configurations. In addition, a theory collaboration was established to study the spin drag in transport through a one-dimensional wire with a publication under review [4].

[1] Laura Corman, Philipp Fabritius, Samuel Häusler, Jeffrey Mohan, Lena H Dogra, Dominik Husmann, Martin Lebrat, and Tilman Esslinger. Quantized conductance through a dissipative atomic point contact. Physical Review A , 100(5):053605, 2019.
[2] Martin Lebrat, Samuel Häusler, Philipp Fabritius, Dominik Husmann, Laura Corman, and Tilman Esslinger. Quantized conductance through a spin-selective atomic point contact. Physical review letters , 123(19):193605, 2019.
[3] Grazia Salerno, Hannah M Price, Martin Lebrat, Samuel Häusler, Tilman Esslinger, Laura Corman, J-P Brantut, and Nathan Goldman. Quantized hall conductance of a single atomic wire: A proposal based on synthetic dimensions. Physical Review X , 9(4):041001, 2019.
[4] A-M Visuri, M Lebrat, S Häusler, L Corman, and T Giamarchi. Spin transport in a one-dimensional quantum wire. arXiv preprint arXiv:2001.08035 , 2020

The researcher has disseminated the results in 6 presentations (conference contributions / invitations / seminars), as well as during two outreach events.
The projects has enabled significant understanding of the optical manipulation of the internal state of ultracold atoms which will be used in the future to investigate strongly correlated systems.
The theoretical proposals in which the researcher was involved propose new way to simulate and detect topological regions in experiments as well as unveil new many-body effects in the spin transport in a finite 1D system.
Illustration of the spin filter.