# Lithium Lab

#### Former Group Members

Diploma/Master’s Student

Postdoc (2015-2018)

Postdoc (2012-2015)

Diploma/Master’s Student

We have built a second-generation quantum gas microscope for fermionic atoms. Our implementation is based on ultracold $^6\mathrm{Li}$ atoms trapped in an optical lattice with 569 nm spacing. We have demonstrated single-site resolved fluorescence imaging for these atoms by using pulsed Raman sideband cooling in a mK deep optical lattice. These techniques are required to overcome the strong recoil heating associated with the light mass of lithium.

##### String patterns in the doped Hubbard model
10/2018
C. S. Chiu, G. Ji, Annabelle Bohrdt, M. Xu, Michael Knap, Eugene Demler, Fabian Grusdt, M. Greiner, D. Greif
Understanding strongly correlated quantum many-body states is one of the most thought-provoking challenges in modern research. For example, the Hubbard model, describing strongly correlated electrons in solids, still contains fundamental open questions on its phase diagram. In this work we realize the Hubbard Hamiltonian and search for specific patterns within many individual images of realizations of strongly correlated ultracold fermions in an optical lattice. Upon doping a cold-atom antiferromagnet we find signatures of geometric strings, entities suggested to explain the relationship between hole motion and spin order, in both pattern-based and conventional observables. Our results demonstrate the potential for pattern recognition and more advanced computational algorithms including machine learning to provide key insights into cold-atom quantum many-body systems.
##### Implementation of a stable, high-power optical lattice for quantum gas microscopy
06/2018
We describe the design and implementation of a stable high-power 1064 nm laser system to generate optical lattices for experiments with ultracold quantum gases. The system is based on a low-noise laser amplified by an array of four heavily modified, high-power fiber amplifiers. The beam intensity is stabilized and controlled with a nonlinear feedback loop. Using real-time monitoring of the resulting optical lattice, we find the stability of the lattice site positions to be well below the lattice spacing over the course of hours. The position of the harmonic trap produced by the Gaussian envelope of the lattice beams is stable to about one lattice spacing and the long-term (six-month) relative RMS stability of the lattice spacing itself is 0.5%.
##### Quantum state engineering of a Hubbard system with ultracold fermions
06/2018
Accessing new regimes in quantum simulation requires the development of new techniques for quantum state preparation. We demonstrate the quantum state engineering of a strongly correlated many-body state of the two-component repulsive Fermi-Hubbard model on a square lattice. Our scheme makes use of an ultralow entropy doublon band insulator created through entropy redistribution. After isolating the band insulator, we change the underlying potential to expand it into a half-filled system. The final many-body state realized shows strong antiferromagnetic correlations and a temperature below the exchange energy. We observe an increase in entropy, which we find is likely caused by the many-body physics in the last step of the scheme. This technique is promising for low-temperature studies of cold-atom-based lattice models.
##### A cold-atom Fermi-Hubbard antiferromagnet
05/2017
A. Mazurenko, C. S. Chiu, G. Ji, M. F. Parsons, M. Kanasz-Nagy, R. Schmidt, F. Grusdt, E. Demler, D. Greif, M. Greiner
09/2016
02/2016
08/2015
05/2015