Thread by @fgrosshans

Now at #QuPa (at @InHenriPoincare), Bruno Laburthe-Tolra from @univ_paris13 on “Some aspects of quantum simulation using cold atoms”
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@InHenriPoincare @univ_paris13 Bruno Laburthe-Tolra: works with quantum gases, with density 10¹²–10¹⁵ at/cm³, at nK or µK, with de Broglie wavelengths and inter-atomic distance > 100nm.
These systems (boson or fermions) are “clean” analogues of condensed matter systems.
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@InHenriPoincare @univ_paris13 Bruno Laburthe-Tolra: Optical lattices are periodic (spin indeendent) potentials induced by stationary optical waves. This allows to make 1D, 2D and 3D potential, making 2D, 1D and strongly correlated spin gases.
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@InHenriPoincare @univ_paris13 Bruno Laburthe-Tolra:Effective spin–spin (Heisenberg like) interaction can arise through Coulomb (condensed matter)/ van der Waals (optical lattice) interaction.
This allows to revisit the Hubbard model from solid-state physics experimentally with cold atoms
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@InHenriPoincare @univ_paris13 Bruno Laburthe-Tolra: The Hubbard model is only an approximate Hamiltonian (dipolar interactions, density assisted tunneling), and the “corrections” can change qualitatively the behaviour

@InHenriPoincare @univ_paris13 Bruno Laburthe-Trola: With cold atoms in periodic potentials, we can directly dive into regime which are intractable by classical computers.
E.g. Interacting spin-less bosons, spin ½ interactiong bosons and fermions, super-exchange interaction
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@InHenriPoincare @univ_paris13 Bruno LAburthe-Tolra: With trapped ions, one can investigate long-range spin-spin interaction.
Bruno LAurthe-Tolra’s main interest is simulation with dipolar particles
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@InHenriPoincare @univ_paris13 Bruno Laburthe-Tolra: Some optical systems allow to change the lattice topology, moving e.g. between decorated triangular, 1D and KAgomé lattices. #LTQI #QuPa

@InHenriPoincare @univ_paris13 Bruno Laburthe-Tolra: Some settings (but not his) have site-resolved imaging. But it needs spaced site ⇒ slow tunneling.
It allows to see the SF–Mott transition atom bu atom (Greiner group) #LTQI #QuPa

@InHenriPoincare @univ_paris13 SF=superfluid #PreviousTweet

@InHenriPoincare @univ_paris13 Bruno Laburthe-Tolra: Greiner‘s group observed the checkerboard pattern with anti-ferromagnetic correlations (s=½ fermions).
Adding doping (away to ½full lattice) is easy experimentally (add holes) but very hard theoretically. Allows to explore a strange metal phase
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@InHenriPoincare @univ_paris13 Brun Laburthe-Tolra: The hard thing experimentally is low temperature, because of spin entropy (close to log(2): ∄ direct way to cool the spins.
The usual strategy relies on super-exchange, but it is VERY long
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Bruno Laburthe-Tolra: It is actually impossible, because the potential is spin insensitive, and conservation laws. The initial spin is ∝√N, because of statistical fluctuations, and we want a regime of total spin close to 0
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Bruno Laburthe-Tolra: It is possible to play with local density, on order to have low spin-entropy regions.
Another way (more promising) is to use spin-dependent hamiltonian. E.g. arxiv:1803.10663 arxiv.org/abs/1803.10663 but other strategies are possible
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Bruno Laburthe-Tolra: For example, unsing spin-orbit coupling allows to copule singlet and triplet and adiabitically engineer the ground state (arxiv.org/abs/1106.1628 / doi.org/10.1103/PhysRe…)
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Bruno Laburthe-Tolra: Has experimental data showing his system is not described by mean-field theory arXiv:1803.02628 arxiv.org/abs/1803.02628 : Helps from theoreticians is needed now to describe current systems!
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