IFA-researcher is lead author in recent paper on single particle density matrices in optical lattices
IFA's Luis Ardila and coworkers study ultracold atoms in optical lattices in Physical Review Letters
![Amplitude and phase deivation versus polarization. Illustration from the paper. Amplitude and phase deivation versus polarization. Illustration from the paper.](/fileadmin/site_files/nyheder/PhysRevLett.121_vifte_1.jpg)
The fact that atomic quantum gases in optical lattices are highly tunable (also in a time-dependent fashion) and well isolated from their environment, makes them an ideal platform for studying coherent many-body quantum dynamics. A striking example is the experimental investigation of many-body localization, a disorder-induced effect where an interacting system does not fully relax to a thermal states but retains a memory of its initial state. Recent experimental results for two-dimensional systems [Science 352, 1547 (2016)] are already beyond what can be investigated numerically on classical computers.
Recently, it has also been achieved to measure densities in optical lattices with single-lattice-site resolution, using quantum-gas microscopes. However, despite this success, it has still not been possible to measure the single-particle density matrix. Having experimental access to this basic quantity, which allows for reconstructing all single-particle expectation values of a given state of matter, would be highly desirable. For example, it has recently been proposed that its spectrum contains unique signatures of many-body localization [Phys. Rev. Lett. 115, 046603 (2015)]. Thus, measuring the single-particle density matrix would allow to test this prediction in systems that are not accessible to numerical simulations.
Rotation of the Pseudo-spin polarisation. Illustration from the paper.
In our manuscript, we propose an experimentally feasible scheme for measuring the single-particle density matrix in optical lattices. It relies on the ability of quantum-gas microscopes to measure occupations and create light-shift potentials both with single-site resolution. On the one hand, we show how to engineer a significant effective tunnel coupling between distant lattice sites. On the other hand, we present a protocol that uses this coupling for reconstructing off-diagonal elements of the single-particle density matrix from measuring site occupations. We believe that our scheme provides a powerful novel tool for quantum simulation in optical lattices.
The authors.