Physicists in the United States, Austria and Brazil have shown that shaking of ultracold Bose-Einstein condensates (BECs) can cause them to either split into uniform segments or crush in unpredictable splinters depending on the frequency of shaking.
"It is noteworthy that the same quantum system can give rise to such different phenomena," said Rice University physicist Randy Hulet, co-author of a study of the work published online in the daily newspaper Physical Review X . The hole lab performed the study's experiments using lithium-BECs, small clouds of ultracold atoms that march into the lock as if they were a single unit or material wave. "The relationship between these states can teach us much about the complex quantity of many body phenomena."
The research was conducted in collaboration with physicists at Austria's Vienna University of Technology (TU Vienna) and Brazil's University in São Paulo in São Paulo Carlos. The experiments lean on Michael Faraday's 1
To investigate Faraday waves, the team limited BEC to a linear one-dimensional waveguide, resulting in a cigar-shaped BEC. The researchers then shook the BECs by a weak, slowly oscillating magnetic field to modulate the strength of interactions between atoms in the 1D waveguide. The Faraday pattern occurred as the frequency of the modulation was set near a collective mode resonance.
But the team also noticed something unexpected: When the modulation was strong and the frequency was far below a Faraday resonance, BEC broke into "grain" of different sizes. Rice researcher Jason Nguyen, lead co-author of the study, found the grain sizes widely distributed and persistent at times even the modulation time.
"Granulation is usually a random process observed in solids such as breaking glass or pulverizing a stone in different sized grains," says study author Axel Lode, who has joint appointments at both TU Vienna and Wolfgang Pauli Institute at the University of Vienna.
Images of the quantum statistics of BEC were identical in each Faraday wave experiment. However, in the granulation experiments, the images looked quite different every time, although the experiments were performed under identical conditions.
Lode said the variation in the granulation experiments arose from quantum correlations – complex relationships between quantum particles that are difficult to describe mathematically.
"A theoretical description of the observations proved to be challenging because standard methods could not reproduce the observations, especially the broad distribution of grain sizes," Lode said. His team helped interpret the experimental results using a sophisticated theoretical method and its implementation in software that accounted for quantum fluctuations and correlations that typical theories do not address.
Hole, Rice's Fayez Sarofim Professor of Physics and Astronomy and a member of the Rice Center for Quantum Materials (RCQM), said the results have important implications for quantum fluid turbulence studies, an unsolved physics problem.
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