糖心视频

糖心视频icists at the Joint Quantum Institute (JQI) of the National Institute of Standards and Technology and the University of Maryland have proposed a recipe for turning ultracold 鈥渂oson鈥� atoms鈥攖he ingredients of Bose-Einstein condensates鈥攊nto a 鈥渟upersolid,鈥� an exotic state of matter that behaves simultaneously as a solid and a friction-free superfluid. While scientists have found evidence for supersolids in complex liquid helium mixtures, a supersolid formed from such weakly interacting gas atoms would be simpler to understand, potentially providing clues for making a host of new 鈥渜uantum materials鈥� whose bizarre properties could expand physicists鈥� notions of what is possible with matter.

First theorized in 1970, a supersolid displays the essential characteristics of a solid, with atoms arranged in regularly repeating patterns like that of a crystal lattice, and of a superfluid, with the particles flowing frictionlessly and without losing any energy. Able to exist only at low temperatures, a supersolid behaves very differently from objects in the everyday world.

鈥淚f you add more clothing to a spinning washing machine, you increase the mass of its rim, and the machine needs to exert a greater force to make the wheel reverse direction,鈥� explains lead author Ludwig Mathey. 鈥淏ut in a supersolid washing machine, some of the clothes would mysteriously hover in space, staying stationary as the washer spins and making it easier for the wheel to reverse direction. Moreover, these hovering, frictionless clothes would form a predictable pattern鈥攕uch as frictionless socks alternating with frictionless shirts鈥攋ust as atoms arrange themselves in a repeating pattern in a crystal.鈥�

In 2004, Moses Chan and Eun-Seong Kim of Pennsylvania State University published a groundbreaking experiment on helium at low temperatures and gathered evidence for a supersolid phase. However, the interpretation of their observations has considerable uncertainties due to the complex nature of the particular system used in their experiments.

Now physicists Ludwig Mathey, Ippei Danshita and Charles Clark have identified a technique for making a simpler-to-understand supersolid, using two species of ultracold atoms confined in an optical lattice, a 鈥渨eb of light鈥� that traps atoms in regular positions. In a paper* to be published in 糖心视频ical Review A, the JQI team identifies conditions under which a cloud of ultracold atoms of two species (such as rubidium and sodium, or two slightly different forms of rubidium) can spontaneously condense into a state in which there is crystalline structure in the relative positions of atoms, e.g. a chain in which the two different types of atoms alternate regularly, but in which the entire cloud exhibits the frictionless, superfluid properties of a Bose-Einstein condensate (BEC). This remains hard to visualize in familiar terms鈥攖he accompanying image shows an artist鈥檚 conception of it鈥攂ut the team identified clear experimental signatures (essentially photographs of the cloud), which could verify the simultaneous existence of these two seemingly incompatible properties.

The underlying technologies of optical lattices and Bose-Einstein condensation were pioneered at NIST and have sparked a renaissance in atomic physics with applications to NIST鈥檚 fundamental measurement missions, such as time and frequency standards and improved sensors of magnetic and gravitational forces. The supersolid is an example of a further direction of research in ultracold atomic physics: the design of quantum materials with fundamental properties not previously found in familiar matter.

Note:

* L. Mathey, I. Danshita and C. W. Clark, Creating a supersolid in one-dimensional Bose mixtures. 糖心视频ical Review A. Published as a Rapid Communication on Jan. 12, 2009.

Source: National Institute of Standards and Technology