Most matter exists in one of three phases: solid, liquid or gas. A fourth phase of matter, plasma, exists in some very high-energy places such as a fire or the core of a star. A fifth state of matter called a Bose–Einstein condensate (BEC) is associated with the lowest energy state possible, that achieved at temperatures near absolute zero. Although not all atoms form BECs on their way to the coldest possible temperature in the Universe, supercooled atoms enter a condensed quantum degenerate regime. All the atoms attempt to obtain the same (lowest) energy state. Quantum degeneracy has been shown for only a handful of elements, among them several alkali metals and ytterbium. Generation of these conditions opens a window to fundamental problems in physics, quantum information processing and quantum optics. EU-funded scientists developed important techniques to expand the range of difficult-to-study phenomena accessible with ultracold atom experiments through work on the project YTTERBIUMSPINLATTICE. An experimental setup to generate optical potentials and to optically trap and cool any stable isotope of ytterbium paves the way to numerous experiments impossible with alkali atoms. The setup enables excitation of atoms to specific nuclear spin states and control and measurement of those states. Since many fundamental properties of ytterbium are not well characterised, scientists began by investigating some of them. These experiments with a quantum gas of ytterbium led to the first direct observation of one of its important properties (spin-exchange interaction energy). The measured value was much higher than expected, so high it will have to be further investigated to determine its impact on experimental strategies. The exchange process was directly observed, paving the way to experimental quantum simulation of condensed-matter models based on orbital interactions. Such experiments include one originally targeted in the proposal. They have been out of reach with ultracold alkali-element atoms. Thus, YTTERBIUMSPINLATTICE has put a powerful new tool in the hands of researchers in the ultracold gases community. Its use promises to shed light on some of the fundamental open issues in physics as well as provide insight for development of novel quantum devices.
Quantum gases, ultracold atoms, quantum degeneracy, ytterbium, optical potentials, spin-exchange interaction