Hidden order found in a quantum spin liquid

An international research team using the UK's world-leading ISIS pulsed neutron and muon source at the STFC Rutherford Appleton Laboratory have detected a new form of quantum order that could have implications for the design of future materials in a range of fields related to nanofabrication and quantum computing. The findings are published online today, 27 July, by the journal Science.

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."

Papers

1. Mesoscopic Phase Coherence in a Quantum Spin Fluid, Guangyong Xu et al 26 July 2007.
2. The one-dimensional quantum spin liquid consisted of chains of nickel-oxygen-nickel atoms (Y₂BaNi0₅).

ISIS

ISIS supports an international community of around 1600 scientists, who use neutrons for research in physics, chemistry, biology, materials science, geology and engineering. A £140 million expansion of ISIS through the building of a Second Target Station is scheduled for completion in 2008.

The work was funded by the Office of Basic Energy Sciences within the U.S. Department of Energy's Office of Science, the National Science Foundation, a Wolfson-Royal Society Research Merit Award (UK), and by the UK Research Councils' Basic Technologies programme. Collaborators on this research include: Collin L. Broholm, Ying Chen and Michel Kenzelmann of Johns Hopkins University and the NIST Center for Neutron Research; Yeong-Ah Soh of Dartmouth College; Gabriel Aeppli of the London Centre for Nanotechnology and University College London; John. F. DiTusa of Louisiana State University; Toshimitsu Ito and Kunihiko Oka of the National Institute of Advanced Industrial Science and Technology (AIST), Japan; and Hidenori Takagi from AIST and University of Tokyo.

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