Transcript PPT | 228.5 KB - Joint Quantum Institute

Using laser speckle to study the relation
between disorder and quantum coherence
A PFC-supported experiment conducted at the Joint Quantum
Institute examines the role of disorder in maintaining quantum
coherence. It does this by introducing disorder into a Bose-Einstein
condensate of rubidium atoms held in an optical lattice to simulate
the role is impurity disorder in high temperature superconductors.
In the JQI condensate, disorder consists of “speckle” delivered by
laser light sent through a diffuser; the slight disorder supplied by the
speckle laser ensures that the atoms retain their coordinated
participation in the unified (BEC) quantum wave structure. But only
up to a point. If too much speckle is added then the quantum
coherence can go away.
The JQI scientists make this visible. They pry their disk-shaped gas
of atoms into two parallel sheets. If the atoms were in a coherent
condition, their collision of the sheets (when the lasers are turned
off) will result in a crisp interference pattern showing up on a video
screen as a series of high-contrast dark and light stripes. If, however,
the imposed disorder had been too high, resulting in a loss of
coherence among the atoms, then the interference pattern will be
washed out. Such patterns are observed.
The resultant paper reports the first direct observation of disorder
causing this kind of fluctuation between phases.
Figure caption
Two thin planes of cold atoms are held in an optical lattice by an array
of laser beams. Still another laser beam, passed through a diffusing
material, adds an element of disorder to the atoms in the form of a
speckle pattern. (Courtesy of Matthew Beeler.)
“Disorder-driven loss of phase coherence in a quasi-2D
cold atom system,” by M C Beeler, M E W Reed, T Hong,
and S L Rolston, in the New Journal of Physics:
http://iopscience.iop.org/13672630/14/7/073024?fromSearchPage=true