Simply Weird Stuff: Making Supersolids withUltracold Gas Atoms13 January 2009

This is an artistic rendition of a supersolid made fromtwo different types of ultracold atoms. The atoms arearranged in a regularly repeating pattern like a solid, butalso can move frictionlessly like a superfluid. Yellowshape represents the electrical forces that the atomsfeel, which vary in a regular pattern. Correspondingly.the density of the atoms (represented by the thickness ofthe spheres) also varies in a periodic fashion. Image:Ludwig Mathey, NIST/JQI

Physicists at the Joint Quantum Institute (JQI) ofthe National Institute of Standards and Technologyand the University of Maryland have proposed arecipe for turning ultracold boson atomstheingredients of Bose-Einstein condensatesinto asupersolid, an exotic state of matter thatbehaves simultaneously as a solid and a friction-free superfluid. While scientists have foundevidence for supersolids in complex liquid heliummixtures, a supersolid formed from such weaklyinteracting gas atoms would be simpler tounderstand, potentially providing clues for makinga host of new quantum materials whose bizarreproperties could expand physicists notions ofwhat is possible with matter.

First theorized in 1970, a supersolid displays theessential characteristics of a solid, with atomsarranged in regularly repeating patterns like that ofa crystal lattice, and of a superfluid, with theparticles flowing frictionlessly and without losingany energy. Able to exist only at low temperatures,a supersolid behaves very differently from objectsin the everyday world.

If you add more clothing to a spinning washingmachine, you increase the mass of its rim, and themachine needs to exert a greater force to make thewheel reverse direction, explains lead authorLudwig Mathey. But in a supersolid washingmachine, some of the clothes would mysteriouslyhover in space, staying stationary as the washerspins and making it easier for the wheel to reversedirection. Moreover, these hovering, frictionlessclothes would form a predictable patternsuch asfrictionless socks alternating with frictionlessshirtsjust as atoms arrange themselves in arepeating pattern in a crystal.

In 2004, Moses Chan and Eun-Seong Kim ofPennsylvania State University published agroundbreaking experiment on helium at lowtemperatures and gathered evidence for asupersolid phase. However, the interpretation oftheir observations has considerable uncertaintiesdue to the complex nature of the particular systemused in their experiments.

Now physicists Ludwig Mathey, Ippei Danshita andCharles Clark have identified a technique formaking a simpler-to-understand supersolid, usingtwo species of ultracold atoms confined in anoptical lattice, a web of light that traps atoms inregular positions. In a paper* to be published inPhysical Review A, the JQI team identifiesconditions under which a cloud of ultracold atomsof two species (such as rubidium and sodium, ortwo slightly different forms of rubidium) canspontaneously condense into a state in which thereis crystalline structure in the relative positions ofatoms, e.g. a chain in which the two different typesof atoms alternate regularly, but in which the entirecloud exhibits the frictionless, superfluid propertiesof a Bose-Einstein condensate (BEC). This remainshard to visualize in familiar termstheaccompanying image shows an artists conception

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of itbut the team identified clear experimentalsignatures (essentially photographs of the cloud),which could verify the simultaneous existence ofthese two seemingly incompatible properties.

The underlying technologies of optical lattices andBose-Einstein condensation were pioneered atNIST and have sparked a renaissance in atomicphysics with applications to NISTs fundamentalmeasurement missions, such as time andfrequency standards and improved sensors ofmagnetic and gravitational forces. The supersolid isan example of a further direction of research inultracold atomic physics: the design of quantummaterials with fundamental properties notpreviously found in familiar matter.

Note:

* L. Mathey, I. Danshita and C. W. Clark, Creating asupersolid in one-dimensional Bose mixtures. Physical Review A. Published as a RapidCommunication on Jan. 12, 2009.

Source: National Institute of Standards andTechnology

APA citation: Simply Weird Stuff: Making Supersolids with Ultracold Gas Atoms (2009, January 13) retrieved15 May 2015 from http://phys.org/news/2009-01-simply-weird-supersolids-ultracold-gas.html

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