Lossy Fermionic Quantum Simulator – LOQUST

The question of dissipation in quantum many-body systems is a subject of considerable interest, for fundamental reasons – associated with the understanding of how many-body quantum correlations survive in presence of decoherence – and for the development of realistic platforms for quantum technologies. In parallel to the question of how dissipation may harm quantum coherences, it has also been suggested to use dissipation in order to create interesting many-body systems – a concept that generalizes that of optical pumping. The idea of dissipative-state engineering is to introduce a controlled coupling to an environment that can induce correlations or symmetries, and can produce or stabilize quantum correlated states. Our project is to combine experimental and theoretical efforts, to explore the dissipative engineering of collective spin states that are relevant for quantum sensing and quantum simulation.
The platform is an ultracold-atom quantum simulator that realizes the Hubbard Hamiltonian in an optical lattice. We will use strontium 87 atoms, a fermionic spin-9/2 species exhibiting a SU(N) spin symmetry – corresponding to an invariance of the system when permuting any two spin states within N spin states, where the number N can be controlled at will from 2 to 10. Based on prior theoretical work, two-body losses in SU(2) or SU(3) systems provide an opportunity to engineer highly-entangled generalized Dicke states, that are of interest to quantum sensing. Our project is to first experimentally verify this possibility, and then study its generalization for SU(N>3) systems, both from the experimental and the theoretical standpoint. For this we will make use of an exceptional tunability that is offered by the narrow lines of strontium atoms, that are of interest to the precision measurement community. In practice, we will use these transitions to engineer losses via photo-association. By simply tuning the magnetic field, these losses can be made either spin-sensitive or spin insensitive, which allows full control over both the strength and the spin selectivity of dissipation. We will also develop a new scheme to drive at will two-body or three-body losses. Due to the local character of losses and the anti-symmetric nature of the few-body wavefunction, those two- and three- body losses specifically target respectively SU(2) or SU(3) singlet states. These capacities will enable an investigation of dissipative quantum dynamics with a full control of the symmetry of the Hamiltonian, from SU(2) to SU(10), and of the symmetry of dissipation.
When losses are low, we generally expect the system to be driven into stationary states that favour triplet correlations. We will study these states, and perform Ramsey sequences to characterize their metrological quality. Furthermore, we will also perform the first study of dynamics of SU(N) lattice gases in the regime of strong dissipation, where the quantum Zeno effect is at play, so that long-lived, strongly correlated many-body states should emerge, with similarities to those that arise in the quantum t-J model at low energy. In both regimes, we will study the robustness of dynamics and of the stationary or metastable states in presence of inhomogeneities, in order to assess the practical usefulness of the highly symmetric novel quantum many-body states that can spontaneously arise in these systems. Therefore, outcomes of this project can find applications to quantum sensing and quantum simulation, that would be directly relevant to alkaline-earth-like species that are currently at the core of optical clocks and atom interferometers.