Summary: Under certain conditions, the atoms in this pigment can lose their individual identities and the assembly of atoms, in effect, acts as one giant atom or condensate.
In research from the National High Magnetic Field Laboratory at the Los Alamos Laboratory in New Mexico featured recently on the cover of Physical Review Letters, a team of scientists from the U.S., Japan, Argentina, and Estonia described how they discovered an ideal candidate for Bose-Einstein condensation in the ancient Chinese pigment, Han Purple. They described how the application of a strong magnetic field to Han Purple (BaCuSi2O6) creates a gas of bosonic spin triplet excitations. The field acts as a chemical potential causing the weakly interacting bosonic gas to undergo Bose-Einstein condensation (BEC) when the temperature is reduced to minus 453 degrees Fahrenheit, six orders of magnitude higher than the temperature normally required for BEC in atomic gases. According to Los Alamos physicist Marcelo Jaime, “the discovery of BEC at such higher temperatures was a surprising scientific advance that will no doubt foster more research in this area."
Chinese chemists synthesised Han Purple pigment from barium copper silicates for the first time roughly 2,000 years ago and used the pigments for pottery and trade, in addition to large imperial projects such as the Qin Terracotta Warriors of Xi'an in Shaanxi Province. Preceding the invention of both paper and the compass, the ancient creation of Han Purple possibly makes it the first man-made compound containing a metallic bond.
A Bose-Einstein condensate is an unusual state of matter that is unlike either liquids or solids. BEC was first predicted in 1925, but it took roughly 70 years of intense theoretical and experimental effort before it was discovered in very dilute atomic gases in 1995. In essence, a BEC is a strange consequence of quantum theory regarding the wave nature of matter: atoms can act like the waves in water or sound in certain ways. At very low temperatures certain types of atoms spontaneously occupy the same quantum state. As a result, the atomic "waves" overlap, forming a giant "matter wave." Each atom loses its identity, the assembly of atoms, in effect, acting as one giant atom or condensate.
The study of the BEC is indispensable to our fundamental understanding of quantum mechanics and could also be utilised in advanced "quantum computers", but very few examples have been found. Besides dilute atomic gases, the BEC is thought to occur in "super-fluid" liquid helium and some forms of superconductivity. The possibility that a magnetic BEC exists in Han Purple represents a significant contribution to quantum physics. The original discovery of the BEC effect has since been confirmed by the same team using new samples prepared simultaneously by other investigators at Los Alamos and at Stanford University.
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