The strontium 87 lab

Quantum magnetism in ensembles of large spin atoms present possibilities beyond those offered by spin ½ electron gases and effective spin ½ atoms, such as magnetic phases with topological properties applicable to quantum information manipulation, or new mechanisms for the emergence of superfluidity. We have built an experimental apparatus that produces ultracold degenerate fermionic gases of strontium 87, with large spin F = 9/2, which we will arranged on periodic potentials produced by interfering lasers (optical lattices).

The large spin of strontium will enable us to emulate situations analog to those encountered by (spin 1/2) electrons in crystalline materials, but also a whole new set of situations that should contrast markedly with those. Furthermore, strontium 87 presents original interaction properties. Indeed, contrary to most species (e.g., chromium), the interactions between two particles do not depend on their spin projections: the Pauli principle, preventing two identical fermionic particles to meet each other and interact, is the only mechanism responsible for magnetism, which leads to an uncommon SU(N) spin rotation symmetry with large consequences on the magnetism.

Our system

On our system, we expect that novel magnetic states will emerge from the interplay between the lattice potential symmetry and the SU(N) spin rotation symmetry: while cubic lattices are suited for long range antiferromagnetic ordering of spin 1/2 particles, they are not expected to be for a large number of spin states. Conversely, triangular geometry may be more suited to antiferromagnetic ordering with three spin states than two. We aim at exploring the effect of these original properties on:

  • the emergence of exotic magnetic phases, ranging from non-conventional spin ordering expected, e.g., for 3 populated spin states in a triangular lattice, to disordered phases such as chiral spin liquids for large number of populated spin states (up to 10 in our experiment). The latter present strong analogies with quantum frustrated magnets and with the topological properties of the quantum Hall states, and present possible applications to quantum information processing.
  • the interplay between exotic magnetic properties and conduction properties when particle transport is allowed, in analogy with the “doping” of magnetic materials which led to the observation of high-Tc electron superconductors.

To reach these goals, our approach is to take advantage of the spectroscopic properties of strontium 87, using know-how from the frequency metrology community. We use the narrow lines of this atomic species – one of which is used in the context of optical clocks – to manipulate and probe the spin degree of freedom of the atomic ensembles. The narrow linewidths lead to unrivaled energy resolution, which we can use, e.g., to target the spins of specific atoms within inhomogeneous external fields (tomography), and to prepare deterministically specific spin patterns and reach towards low energy, low entropy many-body states.

Collaborations 

Project publications

Coherent control over the high-dimensional space of the nuclear spin of alkaline-earth atoms
16/06/2025
Andrea Litvinov, Benjamin Pasquiou, Bruno Laburthe-Tolra, Etienne Maréchal, Husain Ahmed, John H. Huckans, Martin Robert-de-Saint-Vincent, Pauline Guesdon
We demonstrate coherent manipulation of the nuclear degrees of freedom of ultracold ground-state strontium-87 atoms, thus providing a toolkit for fully exploiting the corresponding large Hilbert space as a quantum resource and for quantum simulation experiments with 𝔰u(𝑁)-symmetric matter. arXiv:2501.01731 (2025) / PRX Quantum 6, 020352 (2025)
Effective light-induced Hamiltonian for atoms with large nuclear spin
07/10/2024
Domantas Burba, Emilia Witkowska, Gediminas Juzeliūnas, Hubert Dunikowski, Martin Robert-de-Saint-Vincent
In this paper, we present a systematic derivation of the effective Hamiltonian for the nuclear spin states of ultracold fermionic atoms due to such an off-resonance light. We obtain compact expressions for the scalar, vector, and tensor light shifts taking into account both linear and quadratic contributions to the hyperfine splitting. arXiv:2404.12429 (2024) / Phys. Rev. Research 6, 033293 (2024)
Scalable spin squeezing from spontaneous breaking of a continuous symmetry
17/02/2022
Fabio Mezzacapo, Martin Robert-de-Saint-Vincent, Tommaso Comparin, Tommaso Roscilde
Spontaneous symmetry breaking is a property of Hamiltonian equilibrium states which, in the thermodynamic limit, retain a finite average value of an order parameter even after a field coupled to it is adiabatically turned off. In the case of quantum spin models with continuous symmetry, we show that this adiabatic process is also accompanied by the suppression of the fluctuations of the symmetry generator—namely, the collective spin component along an axis of symmetry. arXiv:2202.08607 (2022) / Phys. Rev. Lett. 129, 113201 (2022)
Measuring densities of cold atomic clouds smaller than the resolution limit
08/09/2021
Andrea Litvinov, Bruno Laburthe-Tolra, Etienne Maréchal, John H. Huckans, Martin Robert-de-Saint-Vincent, Olivier Gorceix, Paolo Pedri, Pierre Bataille
We propose and demonstrate an experimental method to measure by absorption imaging the size and local column density of a cloud of atoms, even when its smallest dimension is smaller than the resolution of the imaging system. arXiv:2105.10296 (2021) / Physical Review A 104, 033309 (2021)
Shelving spectroscopy of the strontium intercombination line
25/10/2019
Anais Molineri, Bruno Laburthe-Tolra, C. Duval, Clémence Briosne-Fréjaville, Etienne Maréchal, Fabrice Wiotte, Isam Manai, Marc Cheneau, Martin Robert-de-Saint-Vincent, Pierre Bataille, Romaric Journet
We present a spectroscopy scheme for the 7 kHz wide 689 nm intercombination line of strontium. We rely on shelving detection, where electrons are first excited to a metastable state by the spectroscopy laser before their state is probed using the broad transition at 461 nm. arXiv:1910.11718 (2019) / J. Phys. B: At. Mol. Opt. Phys. 53 085005 (2020)
Dissipative cooling of spin chains by a bath of dipolar particles
28/03/2018
Bruno Laburthe-Tolra, Martin Robert-de-Saint-Vincent, Paolo Pedri
We consider a spin chain of fermionic atoms in an optical lattice, interacting with each other by super-exchange interactions. We theoretically investigate the dissipative evolution of the spin chain when it is coupled by magnetic dipole–dipole interaction to a bath consisting of atoms with a strong magnetic moment. arXiv:1803.10663 (2018) / New J. Phys. 20 073037 (2018)
Note on the reflectance of mirrors exposed to a strontium beam
23/02/2018
Bruno Laburthe-Tolra, Etienne Maréchal, John H. Huckans, Martin Robert-de-Saint-Vincent, Olivier Gorceix, William Dubosclard
While a number of experiments use heated sapphire windows to reduce strontium deposition and increase the viewport lifetime, here we study another possibility, consisting of sending the laser beam into the atomic flux by reflecting it off a mirror at 45 degree exposed to the strontium flux. We present our attempt to find a substrate that can be exposed to strontium and maintain high reflectivity. arXiv:1802.08499 (2018)

Project news

Generators of the SU(10) group
15/06/2025
Now, with the implementation of evolution operators deriving from the generators of the SU(10) group, complete control over the quantum state of the nuclear spins is achievable. This is an opportunity to use the full Hilbert space of strontium 87 atoms in experiments and for quantum technologies, that we explore in our published paper. For example, we use it to measure simultaneously two non-commuting observables of pseudo-spin ensembles!
New spectroscopy scheme
24/10/2019
We concluded a great collaborative work with Marc Cheneau and his team, at Laboratoire Charles Fabry, on a new spectroscopy scheme for the intercombination line for strontium. For a large spectroscopy signal and a low complexity, look here.
Fermionic degeneracy
01/03/2019
Fermionic degeneracy reached! We now produce 10-component spinor Fermi gases of strontium 87, around half the Fermi temperature.
End of bakeout
01/03/2017
The bake-out is completed, the blue laser system is in place. Oven loading and laser cooling come next.

Funding agencies

ANR, DIM Nano’K, DIM Sirteq, DIM Quantip, Labex FIRST-TF.