Hidden Order Found in a Quantum Spin Liquid

In quantum information processing, data is manipulated using ‘qubits’ – quantum bits. Single electrons make excellent qubits, but interactions with other electrons mean that useable quantum properties are rapidly lost.

The new results are important because they demonstrate explicitly, that in a practical material, a large number of electron spins can be coupled together to yield a quantum state covering around 100 atoms and extending over a distance of 30 nanometres (billionths of a metre). Only a few other examples of such quantum states are known and these lead to fascinating properties such as superconductivity and superfluidity.

“The unique capabilities of neutron scattering have made these latest observations possible,” said Dr Christopher Frost, Instrument Scientist for the MAPS spectrometer at ISIS, and a co-author on the Science paper. “By analysing the images from the instrument, we can establish the perfection of the quantum state.” MAPS is a revolutionary instrument for neutron scattering at ISIS. Using neutron spectroscopy, an intense beam of neutrons is scattered from samples of research material and collected by 100 million detector pixels located over an area of 16 square metres giving a unique view into the interior world of atoms.

The team also discovered that they could manipulate the quantum state, limiting its phase coherence or making it disappear altogether, by introducing defects into the material either by adding chemical impurities or heating.

“Our goal is to understand the factors that affect the distance over which the quantum phase coherence can be maintained and neutron scattering is probably the most direct tool for studying this,” says lead author Guangyong Xu from Brookhaven National Laboratory, USA. “In quantum computing, this state must be must be maintained over a relatively long time in order to store information in the computer. This distance — and how sensitive it is to changes in temperature or chemical impurities in the material — can be essential in determining whether a material will have useful applications.”