Quantum Many Body Systems

Max Planck Institute of Quantum Optics

Hans-Kopfermann-Str. 1

85748 Garching

Group Webpage


Research focus: quantum many-body physics, ultracold quantum gases, quantum simulation

We experimentally study synthetic quantum many-body systems formed out of ultracold atoms in optical lattices. This platform provides a very well isolated and fully controlled quantum system, of which the microscopic properties can be tailored in a wide parameter range. We aim at perfecting the control over this system to explore the intriguing dynamics and correlations in quantum many-body systems at the level of single atoms.

Realizing the Hubbard model

The Hubbard model is the most prominent electronic toy model for the electronic degrees of freedom in high temperature superconductors. We aim to study this model in a clean system, thereby performing a quantum simulation of this in certain regimes computationally intractable problem. To this end, we developed a so called quantum gas microscope for fermionic lithium atoms in an optical lattice. The defining property of a quantum gas microscope is the ability to measure single atoms, in our realization even the spin state of single atoms, in the strongly correlated many-body system. This gives access to novel potentially non-local observable, such as string correlators, and we use them to shed new light onto these systems. We aim to explore the equilibrium correlations between spins and holes at the lowest reachable temperatures, as well as their dynamics in controlled out-of equilibrium situations.

Laser controlled long-range interactions

Quantum magnets are not only often used toy models for the many-body physics in real materials, perfect control over them also enables new technologies in the fields of quantum metrology, simulation and information. In magnets, the only degree of freedom is the local spin and non-trivial systems require interaction between spins at a finite distance. A very promising and flexible way to realize such a setting with ultracold atoms in optical lattices is to use state selective laser coupling to Rydberg states. The Rydberg states feature large electron orbits and hence a large polarizability, with results in very strong interactions extending of the distance of several micrometer. This includes several sites of the optical lattice. Even more, the interaction between the atoms can be tailored by the choice of the Rydberg states and switched almost at will by controlling the laser intensity. We aim to explore the quantum dynamics in such fully controlled quantum magnets and by pushing the limits of control and coherence we aim to realize an artificial quantum system, which can serve as a platform for quantum many-body physics and quantum technologies.


Raman sideband cooling in optical tweezer arrays for Rydberg dressing

N. Lorenz, L. Festa, L.-M. Steinert, C. Gross

Scipost Physics 10, 052 (2021).

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Single neutral atoms trapped in optical tweezers and laser-coupled to Rydberg states provide a fast and flexible platform to generate configurable atomic arrays for quantum simulation. The platform is especially suited to study quantum spin systems in various geometries. However, for experiments requiring continuous trapping, inhomogeneous light shifts induced by the trapping potential and temperature broadening impose severe limitations. Here we show how Raman sideband cooling allows one to overcome those limitations, thus, preparing the stage for Rydberg dressing in tweezer arrays.

DOI: 10.21468/SciPostPhys.10.3.052

Robust Bilayer Charge Pumping for Spin- and Density-Resolved Quantum Gas Microscopy

J. Koepsell, S. Hirthe, D. Bourgund, P. Sompet, J. Vijayan, G. Salomon, C. Gross, I. Bloch

Physical Review Letters 125 (1), 010403 (2020).

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Quantum gas microscopy has emerged as a powerful new way to probe quantum many-body systems at the microscopic level. However, layered or efficient spin-resolved readout methods have remained scarce as they impose strong demands on the specific atomic species and constrain the simulated lattice geometry and size. Here we present a novel high-fidelity bilayer readout, which can be used for full spin- and density-resolved quantum gas microscopy of two-dimensional systems with arbitrary geometry. Our technique makes use of an initial Stern-Gerlach splitting into adjacent layers of a highly stable vertical superlattice and subsequent charge pumping to separate the layers by 21 mu m. This separation enables independent high-resolution images of each layer. We benchmark our method by spin- and density-resolving two-dimensional Fermi-Hubbard systems. Our technique furthermore enables the access to advanced entropy engineering schemes, spectroscopic methods, or the realization of tunable bilayer systems.

DOI: 10.1103/PhysRevLett.125.010403

Time-resolved observation of spin-charge deconfinement in fermionic Hubbard chains

J. Vijayan, P. Sompet, G. Salomon, J. Koepsell, S. Hirthe, A. Bohrdt, F. Grusdt, I. Bloch, C. Gross

Science 10, 186-189 (2020).

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Elementary particles carry several quantum numbers, such as charge and spin. However, in an ensemble of strongly interacting particles, the emerging degrees of freedom can fundamentally differ from those of the individual constituents. For example, one-dimensional systems are described by independent quasiparticles carrying either spin (spinon) or charge (holon). Here, we report on the dynamical deconfinement of spin and charge excitations in real space after the removal of a particle in Fermi-Hubbard chains of ultracold atoms. Using space- and time-resolved quantum gas microscopy, we tracked the evolution of the excitations through their signatures in spin and charge correlations. By evaluating multipoint correlators, we quantified the spatial separation of the excitations in the context of fractionalization into single spinons and holons at finite temperatures.


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