Imaging of Matter
Shaking up fermions into higher Bloch bands shapes new generation of quantum simulators
15 July 2021
Photo: AG Hemmerich
For the first time, researchers at Universität Hamburg have loaded a fermionic quantum gas of neutral atoms into selected higher Bloch bands of an optical lattice. The work sets the stage for new fundamental insights into fermionic superfluidity in the presence of orbital degrees of freedom. The researchers led by Prof. Andreas Hemmerich from the Institute of Laser Physics and the Cluster of Excellence "CUI: Advanced Imaging of Matter" report on their work in the journal Physical Review Letters.
Optical lattices are synthetic arrays of bosonic or fermionic neutral atoms or molecules trapped in laser-induced periodic potentials. Aside from their practical use in atomic clock applications they are celebrated as an ideal toolbox for quantum simulation of lattice physics. Fermionic particles are particularly important in this context, since they take on the role of electrons tunneling and interacting in a lattice of ionic cores. However, many of the fascinating functionalities such as metal-insulator transitions, superconductivity and magnetoresistance are based on orbital degrees of freedom.
Previous techniques have not yet led to the desired results for many-body physics: for example, researchers recently simulated orbital single-particle wave functions with electrons in the second band of an artificial square lattice made of carbon monoxide atoms arranged on a copper surface. It is however not obvious, how this scenario could be extended to emulate many-body physics. A natural approach to extend optical lattices with fermionic atoms to include higher Bloch bands, is to load sufficiently many atoms. This, however, requires multiply occupied lattice sites and hence leads to deleterious collisions. An alternative approach, that was pioneered for bosonic atoms, selectively excites the atoms from the lowest band into a desired higher target band, thus keeping the site occupation low.
“For the first time, we used similar techniques to form fermionic optical lattices with orbital degrees of freedom,” Hemmerich explains. Extreme band lifetimes demonstrate the exquisite robustness of the system, momentum spectra confirm the orbital character of the lattice. “We think that the techniques we describe should prove useful for an advanced generation of quantum simulators for electronic matter with orbital degrees of freedom”, says Hemmerich.
M. Hachmann, Y. Kiefer, J. Riebesehl, R. Eichberger, A. Hemmerich
"Quantum degenerate Fermi gas in an orbital optical lattice"
Phys. Rev. Lett. 127, 21, 033201 (2021), highlighted as Editors' Suggestion