In Summary

A team of Australian and Italian scientists has made a new experimental observation, proving a theoretical prediction and revealing a versatile tool for exploring new horizons in diverse branches of physics.

In a paper published in the prestigious Nature Physics, theoretical scientists Associate Professors Xia-Ji Liu and Hui Hu, from the Centre for Quantum and Optical Science at Swinburne University of Technology, collaborated with researchers at the European Laboratory for Non-linear Spectroscopy (LENS) to realise one-dimensional quantum liquid of fermions with tunable spin.

“The central aim was to emulate a simple text-book model to better understand complex behaviours of strongly interacting electrons confined in low dimensions – such as high-temperature superconductors – using a table-top system of ultracold atoms,” Associate Professor Liu said.

The rapidly developing field of ultracold atoms was established following Nobel Prize-winning research on laser cooling of atoms and Bose-Einstein condensation.

“A cloud of atoms can be cooled down to incredibly low temperatures of a billionth of a degree Kelvin,” Associate Professor Hu said.

“At these temperatures, fermionic atoms, as the atomic analogue of electrons and protons which are the building blocks of all matter, can occupy quantum states one by one, precisely following the rule of quantum mechanics.”

A unique aspect of ultracold atoms is their controllability – a vast range of interactions, geometries and dimensions is possible. Using Feshbach resonances and applying a magnetic field at the right strength, interactions between atoms can be controlled with great precision – from arbitrarily weak to arbitrarily strong.

“Using an optical lattice, a set of standing wave lasers that trap atoms, one can create artificial one- or two-dimensional environments to explore how physics changes with dimensionality,” Associate Professor Hu said.

At LENS, Leonardo Fallani and Massimo Inguscio and their colleagues cooled fermionic ytterbium 173Yb atoms down to near absolute zero.

Using two pairs of standing wave lights, the ultracold atoms with six possible nuclear spin orientations were trapped in a two-dimensional crystal-like structure, forming a bundle of independent one-dimensional quantum liquids with tunable spin.

“This discovery could lead to potential applications in future quantum technologies such as fault-tolerant quantum computers,” Associate Professor Liu said.

“The creation of the new state of matter in this work, promises an exciting new way to understand counterintuitive one-dimensional physics, such as the complete separation of spin and charge excitations.

“It opens up the investigation of fundamental effects, ranging from spin dynamics to novel magnetic phases which could be useful in the emerging technology of spintronics.”